Anode composition, anode for lithium secondary battery, 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, 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. 10-2022-0037219, filed with the Korean Intellectual Property Office on March 25, 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, and a lithium secondary battery including the negative electrode. [Background technology]

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

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

[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 are 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 comprises 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. However, while silicon-based compounds, which are high-capacity materials, have a higher capacity than conventionally used graphite, they suffer from a problem in that their volume expands rapidly during charging, disrupting the conductive path and degrading 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 of adjusting the driving potential, methods of additionally coating a thin film on the active material layer, methods of suppressing volume expansion itself, such as methods of adjusting the particle size of the silicon-based compound, or various methods of preventing the conductive path from being broken. However, these methods have limitations in their application because they may actually reduce battery performance, and there are still limitations in the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0009] Therefore, in the process of manufacturing a silicon-based negative electrode to maximize capacity characteristics, research is needed into a negative electrode composition that can prevent the volume expansion and surface cracking caused by charge and discharge. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0011] In silicon-based negative electrodes, a negative electrode binder is used to control volume expansion due to charging and discharging, and a negative electrode conductive material is used to maintain the conductive path, but the problem of volume expansion due to charging and discharging remains unresolved.

[0012] As a result of research to solve the above problems, it was found that this can be controlled when a specific content of a carbon-based material under predetermined conditions is included in the negative electrode composition.

[0013] Therefore, the present application relates to a negative electrode composition that can solve the above problems, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0014] One embodiment of the present specification provides a negative electrode composition including a silicon-based active material; a negative electrode conductive material; a negative electrode binder; and a carbon-based material, wherein the carbon-based material is included in an amount of 15 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and the carbon-based material has a charge capacity of 400 mAh / g or more, a discharge capacity of 350 mAh / g or more, and a charge / discharge efficiency of 90% or less.

[0015] 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.

[0016] Finally, 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. [Effects of the Invention]

[0017] The negative electrode composition according to the present application contains a silicon-based active material to increase the capacity of the negative electrode, and also contains a specific amount of a carbon-based material that functions as a negative electrode active material and meets certain requirements, thereby more effectively preventing volume expansion during charge and discharge than when the negative electrode composition contains only a silicon-based active material.

[0018] In addition, the anode composition according to the present application has the above-described composition, and during primary charging, lithium ions are simultaneously charged to the carbon-based material and the silicon-based active material, and due to the difference in capacity between the active materials, lithium ions are simultaneously transferred to the silicon-based active material with a larger capacity. This improves the diffusion of lithium ions, resulting in improved overall charging uniformity of the silicon-based anode.

[0019] Furthermore, the anode composition according to the present application contains a specific content of a carbon-based material that meets specific conditions. When a carbon-based material having lower charge and discharge efficiency than a silicon-based active material is used, excess lithium ions are accumulated in a portion of the silicon-based active material, thereby achieving the effect of pre-lithiation, and the anode composition according to the present application exhibits excellent effects in a silicon-based anode whose performance improves depending on the depth of charge.

[0020] Finally, the carbon-based material in which the charged lithium ions are diffused into the silicon-based active material is a conductive material, and remains in the anode, improving the conductivity within the electrode. [Brief explanation of the drawings]

[0021] [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. DETAILED DESCRIPTION OF THE INVENTION

[0022] Prior to describing the present invention, some terms will first be defined.

[0023] 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.

[0024] In this specification, "p to q" means "not less than p and not more than q."

[0025] 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 (median 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, the median particle size may be measured using a 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 depending on the particle size is measured to calculate the particle size distribution.

[0027] In one embodiment of the present application, the particle size or particle diameter may refer to the average diameter or representative diameter of each particle constituting the particle.

[0028] 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.

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

[0030] 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.

[0031] 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 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.

[0032] One embodiment of the present specification provides a negative electrode composition including a silicon-based active material; a negative electrode conductive material; a negative electrode binder; and a carbon-based material, wherein the carbon-based material is included in an amount of 15 parts by weight or less based on 100 parts by weight of the negative electrode composition, and the carbon-based material has a charge capacity of 400 mAh / g or more, a discharge capacity of 350 mAh / g or more, and a charge / discharge efficiency of 90% or less.

[0033] The negative electrode composition according to the present application contains a silicon-based active material to increase the capacity of the negative electrode, and also contains a specific amount of a carbon-based material that functions as a negative electrode active material and meets the above requirements, thereby more effectively preventing volume expansion during charge and discharge than when the negative electrode composition contains only a silicon-based active material.

[0034] The negative electrode composition according to the present application will be described in detail below.

[0035] In one embodiment of the present application, there is provided a negative electrode composition in which the carbon-based material includes graphite.

[0036] The carbon-based material according to the present application has a different role and structure from artificial graphite and natural graphite used as conventional negative electrode active materials and from plate-like graphite used as conventional negative electrode conductors. Unlike artificial graphite and natural graphite used as negative electrode active materials and plate-like graphite used as conventional negative electrode conductors, the carbon-based material has low charge / discharge efficiency, resulting in a high charge capacity and a low discharge capacity. In the present application, a low discharge capacity means that the carbon-based material retains some lithium ions during discharge.

[0037] That is, the carbon-based material according to the present application has smaller particles, superior output characteristics, and a specific range of charge-discharge efficiency compared to conventional natural or artificial graphite because of its low degree of graphitization, and the use of a material with a charge-discharge efficiency within the range of the present application is due to the range of use of the silicon-based active material. Lithium ions charged in the graphite all migrate to the silicon-based active material, which has a large capacity and a high potential. At this time, the higher the charge amount of the graphite (i.e., the lower the charge-discharge efficiency), the more Li ions the graphite contains, which results in the silicon-based active material being able to contain more lithium. Ultimately, the use of the carbon-based material according to the present application allows the range of use of the silicon-based active material to be more stable.

[0038] In one embodiment of the present application, there is provided a negative electrode composition, wherein the carbon-based material has a charge capacity of 400 mAh / g or more, a discharge capacity of 350 mAh / g or more, and a charge / discharge efficiency of 90% or less.

[0039] In another embodiment, the charge capacity of the carbon-based material may be 400 mAh / g or more, preferably 410 mAh / g or more, more preferably 420 mAh / g or more, and may satisfy the range of 600 mAh / g or less, preferably 550 mAh / g or less.

[0040] In another embodiment, the discharge capacity of the carbon-based material may be 350 mAh / g or more, and may be 500 mAh / g or less, preferably 450 mAh / g or less.

[0041] In one embodiment of the present application, the charge / discharge efficiency of the carbon-based material can satisfy the range of 90% or less, preferably 87% or less, and can satisfy the range of 70% or more, more preferably 75% or more.

[0042] The carbon-based material according to the present invention satisfies the above-described charge capacity, discharge capacity, and charge / discharge efficiency. Therefore, when included in a negative electrode composition, it can function as an active material. That is, by satisfying the above-described ranges, lithium ions are simultaneously charged to the carbon-based material and the silicon-based active material, and due to the difference in capacity between the active materials, lithium ions are simultaneously transferred to the silicon-based active material with a larger capacity. This improves lithium ion diffusion, thereby improving the overall uniformity of charge in a silicon-based negative electrode containing the carbon-based material. However, unlike artificial graphite or natural graphite used in conventional negative electrode active materials, the carbon-based material according to the present invention has a charge / discharge efficiency of 90% or less. It contains excess lithium ions that can be accumulated in some silicon-based active materials, thereby achieving a prelithiation effect, and is therefore advantageous in silicon-based negative electrodes, where performance improves with depth of charge.

[0043] In one embodiment of the present application, there is provided a negative electrode composition, wherein the functional group content (volatile matter) of the carbon-based material is 1.0% or more.

[0044] In one embodiment of the present application, the functional group content (volatile content) is a numerical representation of the content of functional groups contained in a carbon-based material, which can be calculated using the weight loss rate as follows:

[0045] Weight loss rate = [(weight of material before heat treatment - weight of material after heat treatment) / weight of material before heat treatment] x 100

[0046] The amount lost by the heat treatment may be a functional group present on the surface of the material before the heat treatment, and the functional group may be at least one selected from the group consisting of a hydroxy group, a carboxy group, an aldehyde group, a phenol group, a ketone group, an anhydride group, a lactone group, a peroxide (oxide), an ether group, a hemiacetal group, a quinone group, and an amine group.

[0047] The functional group content (volatile content) according to the present application is measured using an analytical method that can confirm the mass while increasing the temperature using thermal analysis. The method used in the present application is the TPD mass method, specifically, a method in which the measurement sample is heated up to 950°C and the amount of volatilized compounds is confirmed. The analyzed amount can be expressed as the content of functional groups present on the surface of the carbon-based material.

[0048] In one embodiment of the present application, the functional group content (volatile content) of the carbon-based material may be in the range of 1.0% or more, preferably 1.3% or more, and may be in the range of 5% or less, more preferably 4.5% or less, and most preferably 4.0% or less.

[0049] The negative electrode composition according to the present application corresponds to a silicon-based electrode containing a silicon-based active material as a main material. In this case, the functional group content of the carbon-based material satisfies the above range, thereby improving dispersibility in an aqueous system and thereby maximizing the effect of storing and transporting lithium ions in the negative electrode composition.

[0050] The carbon-based material according to the present application has a low degree of graphitization and a low charge / discharge efficiency. The degree of graphitization is adjusted by high-temperature firing, and at this time, the content of functional groups can be adjusted within the above range by adjusting the degree of graphitization (by adjusting the firing temperature).

[0051] In one embodiment of the present application, there is provided a negative electrode composition in which the median particle diameter (D50) of the carbonaceous material is 10 μm or less.

[0052] In another embodiment, the median particle diameter (D50) of the carbonaceous material can satisfy 10 μm or less, preferably 8 μm or less, more preferably 7 μm or less, and can satisfy a range of 1 μm or more, preferably 3 μm or more.

[0053] In one embodiment of the present application, based on 100 parts by weight of the negative electrode composition, the carbonaceous material may be contained in 15 parts by weight or less, preferably 13 parts by weight or less, more preferably 12 parts by weight or less, and may be contained in 1 part by weight or more, preferably 5 parts by weight or more.

[0054] In the case of the negative electrode composition according to the present application, while containing a silicon-based active material having excellent capacity characteristics as a main active material, it is characterized by containing a carbonaceous material having the above characteristics in the above content parts. That is, while maximizing the capacity characteristics of the negative electrode composition itself, a carbonaceous material having lower capacity characteristics than the silicon-based active material is contained in the above content parts. When using a carbonaceous material having lower charge and discharge efficiency than the silicon-based active material, extra lithium ions can be accumulated in some silicon-based active materials while obtaining the effect of pre-lithiation, and in a silicon-based negative electrode in which the performance is improved depending on the depth of charge, it has the characteristic of having an excellent effect.

[0055] In one embodiment of the present application, there is provided a negative electrode composition in which the silicon-based active material contains one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0056] In one embodiment of the present application, the silicon-based active material contains 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) may be contained in 70 parts by weight or more.

[0057] In another embodiment, based on 100 parts by weight of the silicon-based active material, 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 of the SiOx (x=0), and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0058] In one embodiment of the present application, the silicon-based active material may be, in particular, pure silicon (Si). Using pure silicon (Si) as the silicon-based active material may mean that pure Si (SiOx (x=0)) not bonded to other particles or elements is contained within the above range, based on 100 parts by weight of the total silicon-based active material.

[0059] 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 the above 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 above lower limit 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 the above range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0060] 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 to 150.0 m 2 / g, more preferably 0.1 to 100.0 m 2 / g, particularly preferably 0.2 to 80.0 m 2 / g, most preferably 0.2 to 18.0 m2 / g. The BET specific surface area is determined according to DIN 66131 (using nitrogen).

[0061] 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.

[0062] In one embodiment of the present application, the silicon-based active material may be 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0063] In yet another embodiment, the silicon-based active material may comprise 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 comprise 90 parts by weight or less, preferably 85 parts by weight or less, more preferably 80 parts by weight or less.

[0064] The anode composition according to the present application is characterized in that it can control the volume expansion rate during charge and discharge even when using a silicon-based active material with a significantly high capacity within the above range, and contains a predetermined amount of a specific carbon-based material that does not cause any problems with capacity characteristics, thereby exhibiting high capacity characteristics and improving the life characteristics of the electrode.

[0065] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the circularity 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.

[0066] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter.

[0067] [Formula 1] 4πA / P 2

[0068] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into batteries to increase capacity have recently been increasing in response to growing demand for high-capacity batteries. However, even if silicon-based active materials can partially adjust their properties as described above, their volume can suddenly expand during charge / discharge processes, potentially damaging the conductive pathways formed within the negative electrode active material layer.

[0069] 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.

[0070] In one embodiment of the present application, the dot-like conductive material refers to a spherical or dot-like conductive material that can be used to improve the conductivity of a negative electrode and has conductivity without inducing chemical changes. 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 achieving high conductivity and excellent dispersibility.

[0071] 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.

[0072] In one embodiment of the present application, the point-like conductive material can have a functional group content (volatile content) 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.

[0073] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, functional groups are present on the surface of the dot-shaped conductive material, and when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent.

[0074] 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.

[0075] 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.

[0076] In one embodiment of the present application, the negative electrode conductive material may include a sheet conductive material.

[0077] The planar conductive material increases the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time, prevents the conductive path from being broken due to volume expansion. The planar conductive material may be referred to as a plate-type conductive material or a bulk-type conductive material.

[0078] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of plate-like graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-like graphite.

[0079] 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 above range is satisfied, the particle size is sufficient, making dispersion easy while preventing excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersing using the same device and time, the dispersion effect is excellent.

[0080] 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 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0081] 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.

[0082] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material with a high specific surface area or a sheet conductive material with a low specific surface area without any restrictions. However, since the sheet conductive material according to the present application may have electrode performance that is affected to some extent by dispersion, it is particularly preferable to use a sheet conductive material with a low specific surface area that does not cause dispersion problems.

[0083] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0084] In another embodiment, the sheet conductive material has a BET specific surface area of ​​5 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.

[0085] 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.

[0086] 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 ​​5 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.

[0087] 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 with the longitudinal axes of the carbon nanotube units substantially aligned in the same direction, or twisted into 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.

[0088] In one embodiment of the present application, the linear conductive material may include SWCNT; or MWCNT.

[0089] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material comprises one or more selected from the group consisting of dot-like conductive materials; planar conductive materials; and linear conductive materials, and the negative electrode conductive material is included in an amount of 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0090] In yet another embodiment, the negative electrode conductive material may be included in an amount of 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 0.2 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0091] In one embodiment of the present application, the negative electrode conductive material may include a linear conductive material.

[0092] In particular, in one embodiment of the present application, the negative electrode conductive material includes a linear conductive material and satisfies the above-mentioned composition and ratio, thereby providing the characteristics of increased points at which charging and discharging are possible and excellent output characteristics at a high C rate without significantly affecting the life characteristics of conventional lithium secondary batteries.

[0093] The negative electrode conductive material according to the present application has a completely different structure from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to control the contact points between the silicon-based active material, which experiences a large volume expansion of the electrode during charging and discharging, while the positive electrode conductive material serves to provide a buffer and some conductivity during rolling, and is completely different in structure and role from the negative electrode conductive material of the present invention.

[0094] 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.

[0095] 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 conventional negative electrode active material. It also has a structure and function different from that of the carbon-based material of the present application. Specifically, the carbon-based active material used only as a conventional 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.

[0096] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and may be expressed as plate-shaped graphite. That is, the planar conductive material 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 serves to ensure a planar conductive path within the negative electrode active material layer.

[0097] That is, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material that ensures a conductive path rather than storing or releasing lithium. In this case, the negative electrode active material included 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.

[0098] Meanwhile, in the present application, the use of a carbon-based active material as an active material means that the carbon-based active material is processed into a dotted or spherical shape and is used as a material that stores or releases lithium.

[0099] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is dot-shaped and has a BET specific surface area of ​​0.1 m 2 / g or more and 4.5m 2 / g or less. In addition, the plate-type graphite, which is a planar conductive material, is planar and has a BET specific surface area of ​​5m 2 / g or more.

[0100] 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.

[0101] The negative electrode binder according to one embodiment of the present application serves to control the active material and conductive material in order to prevent twisting and deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. As long as the binder fulfills the above-mentioned role, any conventional binder may be used. Specifically, a water-based binder may be used, and more specifically, a PAM-based binder may be used.

[0102] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the negative electrode binder includes a water-based binder, and the amount of the negative electrode binder is 5 parts by weight or more and 15 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0103] In yet another embodiment, the amount of the negative electrode binder may be 5 parts by weight or more and 15 parts by weight or less, preferably 7 parts by weight or more and 13 parts by weight or less, and more preferably 9 parts by weight or more and 12 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0104] The negative electrode for a lithium secondary battery according to the present application uses a silicon-based active material to maximize capacity characteristics, and exhibits greater volume expansion during charge and discharge than a conventional negative electrode using a carbon-based active material as the main active material. Therefore, by including a large amount of the anode binder, the negative electrode can efficiently control the volume expansion of the highly rigid silicon-based active material during charge and discharge.

[0105] 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.

[0106] 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.

[0107] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by applying a negative electrode slurry containing the negative electrode composition to one or both surfaces of a negative electrode current collector layer and drying the applied slurry.

[0108] In this case, the negative electrode slurry may include the above-described negative electrode composition and a slurry solvent.

[0109] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0110] 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%.

[0111] 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.

[0112] 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.

[0113] In one embodiment of the present application, the slurry solvent may be any solvent that can dissolve the negative electrode composition, and specifically, water, acetone, or NMP may be used.

[0114] 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.

[0115] 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.

[0116] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0117] 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.

[0118] 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.

[0119] 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 allowing the electrode to have appropriate ranges of electrical conductivity and resistance.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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, calcined 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 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0125] 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 Mc3 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, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); 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 Li-metal.

[0126] 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.

[0127] 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. 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0132] 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.

[0133] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred 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 linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and thus these cyclic carbonates are more preferred.

[0134] 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:

[0135] 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.

[0136] 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. [Example]

[0137] 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.

[0138] <Production example> <Production of negative electrodes> <Examples 1 to 4 and Comparative Examples 1 to 4> A negative electrode slurry was prepared by adding silicon (average particle size (D50): 3.5 μm) as a silicon-based active material, graphite (satisfying the properties listed in Table 1 below) as a carbon-based material, SWCNTs, and polyacrylamide (PAM) as a binder in a weight ratio of 80:10:0.21:9.79 to distilled water as a solvent for forming a negative electrode slurry (solid concentration: 25 wt%).

[0139] The SWCNTs have a BET specific surface area of ​​1000 to 1500 m 2 / g and an aspect ratio of 10,000 or more.

[0140] Specifically, the SWCNTs, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material and graphite, a carbon-based material, were added and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0141] The negative electrode current collector layer was made of a copper current collector (thickness: 26 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 87.7 mg / 25 cm. 2 The coated material was rolled 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 electrodes of Examples 1 to 4 and Comparative Examples 1 to 4 (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0142] For reference, the graphite used as the carbon-based material in Comparative Examples 1 and 2 corresponds to natural graphite, which is a common carbon-based active material, and the graphite used as the carbon-based material in Comparative Examples 3 and 4 corresponds to artificial graphite, which is a common carbon-based active material.

[0143] [Table 1]

[0144] <Comparative Example 5> A negative electrode was fabricated in the same manner as in Example 1, except that a silicon-based active material, Si (average particle size (D50): 3.5 μm), a carbon-based material of Comparative Example 3, graphite (artificial graphite), SWCNT, CMC, and SBR were added to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 9.79:86:0.21:1:3 to prepare a negative electrode slurry.

[0145] <Comparative Example 6> A silicon-based active material, Si (average particle size (D50): 3.5 μm), the carbon-based material of Example 1, SWCNT, and polyacrylamide (PAM) as a binder were added to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 40:50:0.21:9.79 to prepare a negative electrode slurry (solid concentration: 25 wt %).

[0146] <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%).

[0147] 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%).

[0148] A polyethylene separator was interposed between the positive electrode and the negative electrode of Example 1, and an electrolyte was injected thereinto to prepare a secondary battery of Example 1.

[0149] The electrolyte was prepared by adding 3 wt% vinylene carbonate (VCO) to an organic solvent containing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 30:70, based on the total weight of the electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0150] Secondary batteries were fabricated in the same manner as above, except that the negative electrodes of the Examples and Comparative Examples were used.

[0151] [Experimental Example 1: Coin Half-Cell Life Evaluation] The secondary battery manufactured as described above was subjected to a life evaluation using an electrochemical charger / discharger.

[0152] The coin half-cell battery was charged (0.5C CC / CV charge, capacity cut (1800mAh / G, 50% of Si capacity)) and discharged (0.5C CC discharge, 1.0V cut) to check the number of cycles until the capacity retention rate reached 80%. The results are shown in Table 2 below.

[0153] The capacity retention rate at the Nth cycle was evaluated using the following formula.

[0154] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0155] [Table 2]

[0156] [Experimental Example 2: Evaluation of Monocell Life] The secondary battery manufactured as described above was subjected to a life evaluation using an electrochemical charger / discharger.

[0157] The number of cycles required to reach a capacity retention rate of 80% was determined under the conditions of charging (1.0C CC / CV charging 4.2V 0.05C cutoff) and discharging (0.5C CC discharging 3.0V cutoff) of the mono-cell battery. The results are shown in Table 3 below.

[0158] The capacity retention rate at the Nth cycle was evaluated using the following formula.

[0159] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0160] [Table 3]

[0161] Unlike the artificial graphite and natural graphite (Comparative Examples 1-4) used in negative electrode active materials and the flake graphite used in conventional negative electrode conductive materials, the carbon-based material according to the present application has low charge / discharge efficiency, resulting in a high charge capacity and a low discharge capacity. Based on the results of the above examples and comparative examples, the negative electrode composition according to the present application has the above-described composition, and during primary charging, lithium ions are simultaneously charged to the carbon-based material and the silicon-based active material, and due to the difference in capacity between the active materials, lithium ions are simultaneously transferred to the silicon-based active material, which has a larger capacity. This improves lithium ion diffusion, resulting in improved overall charge uniformity for silicon-based negative electrodes containing the composition.

[0162] The carbon-based materials of Comparative Examples 1 to 4 correspond to materials with high charge / discharge efficiency and low functional group content. In these cases, unlike Examples 1 to 4, the carbon-based materials with high charge / discharge efficiency were unable to store excess lithium ions, and performance did not improve depending on the depth of charge, resulting in poorer evaluation of lifespan compared to Examples 1 to 4.

[0163] Comparative Example 5 corresponds to a carbon-based electrode, not a silicon-based electrode, using a high content of graphite (artificial graphite) as the carbon-based material. The electrode was fabricated based on the same capacity as the examples, resulting in a thick electrode. This resulted in a decrease in the electrode's conductivity and C-rate characteristics, resulting in a decrease in lifespan and electrode performance. Furthermore, in Comparative Example 5, significant detachment occurred due to insufficient electrode adhesion during the electrode fabrication process and an excessively thick electrode. The decrease in performance with cycling corresponds to a decrease in C-rate characteristics due to the increased electrode thickness.

[0164] Comparative Example 6 is a case where the silicon-based electrode contains a high content of the carbon-based material according to the present application. In this case, as in Comparative Example 5, the electrode becomes thicker in order to achieve the same capacity as in the Examples. As a result, the C-rate characteristics (output characteristics) of the electrode decrease, and as in Comparative Example 5, it was confirmed that the lifespan and electrode performance decrease. [Explanation of symbols]

[0165] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 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; a negative electrode binder; and a carbon-based material, The carbon-based material is included in an amount of 15 parts by weight or less based on 100 parts by weight of the negative electrode composition, The carbon-based material has a charge capacity of 400 mAh / g or more, a discharge capacity of 350 mAh / g or more, and a charge / discharge efficiency of 90% or less; the carbon-based material is graphite; The carbon-based material has a median particle size (D50) of 1 μm or more and 10 μm or less, The functional group content (volatile content) of the carbon-based material is 1.0% by weight or more and 5.0% by weight or less; The silicon-based active material is SiOx (x=0), and the silicon-based active material has an average particle size (D50) of 5 μm or more and 10 μm or less.

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

3. the negative electrode conductive material includes at least one selected from the group consisting of a dot-like conductive material; a sheet-like conductive material; and a linear conductive material; The negative electrode composition according to claim 1 , wherein the negative electrode conductive material is contained in an amount of 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of the negative electrode composition.

4. 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 3, formed on one or both surfaces of the negative electrode current collector layer. A negative electrode for a lithium secondary battery comprising:

5. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 5. The negative electrode for a lithium secondary battery according to claim 4, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

6. Positive electrode; The negative electrode for a lithium secondary battery according to claim 4; a separator disposed between the positive electrode and the negative electrode; and electrolyte A lithium secondary battery comprising:

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