Anode active material, anode composition, lithium secondary battery anode comprising same, and lithium secondary battery comprising anode

Abstract

The present application relates to an anode active material, an anode composition, a lithium secondary battery anode comprising same, and a lithium secondary battery comprising the anode.

Description

Negative active material, negative electrode composition, negative electrode for lithium secondary battery including the same, and lithium secondary battery including the negative electrode

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0190996, filed with the Korean Intellectual Property Office on December 26, 2023, the entire contents of which are incorporated herein by reference.

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

[0003] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the most actively researched field is power generation and storage using electrochemical reactions.

[0004] A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used. Furthermore, active research is being conducted on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for these high-capacity lithium secondary batteries.

[0006] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and deintercalates lithium ions from the positive electrode. Silicon particles with a high discharge capacity can be used as the negative electrode active material.

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

[0008] Accordingly, in order to solve the problems when using a silicon-based compound as an anode active material, various methods are being discussed, such as a method for controlling the driving potential, a method for additionally coating a thin film on the active material layer, a method for controlling the particle size of the silicon-based compound, a method for suppressing the volume expansion itself, or a method for preventing the conductive path from being cut off. However, the above methods may actually lower the performance of the battery, so there are limitations in their application, and there are still limitations in the commercialization of anode batteries with a high silicon-based compound content.

[0009] Furthermore, silicon-based anode active materials suffer from low initial efficiency due to their high irreversibility. To overcome this, lithium doping has been known to increase initial efficiency, and research has confirmed its effectiveness in improving cycle performance. However, these highly efficient silicon-based active materials pose a risk of explosion due to the generation of H2 gas during slurry preparation and storage, as well as poor phase stability.

[0010] Therefore, even when using a silicon-based active material as an anode active material to improve capacity performance, it is necessary to research a stable anode active material itself that can prevent damage to the conductive path due to volume expansion of the silicon-based compound and solve the problem of hydrogen gas generation during slurry production and storage.

[0011] <Prior Art Literature>

[0012] Japanese Patent Publication No. 2009-080971

[0013] In order to solve problems such as stability and gas defects in the electrode manufacturing process of a negative electrode slurry containing a silicon-based active material, a study on the amount of hydrogen gas generated was conducted. As a result, a coating layer was formed on the surface of the silicon-based active material, and it was found through research that when the thickness of the coating layer is formed to a specific thickness compared to the average particle diameter (D50) of the silicon-based active material, the pH of the negative electrode active material can change, and thus the stability of the slurry can be improved.

[0014] Accordingly, the present application relates to a negative electrode active material capable of solving the above-mentioned problems, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

[0015] One embodiment of the present specification provides a negative electrode active material comprising a silicon-based active material; and a coating layer provided on the surface of the silicon-based active material; wherein the coating layer includes a carbon-based material, and the thickness of the coating layer satisfies the following formula 1.

[0016] [Formula 1]

[0017] Silicon-based active material average particle size (D50) / 70 < coating layer thickness < silicon-based active material average particle size (D50) / 10

[0018] In another embodiment, an object of the present invention is to provide a negative electrode composition comprising a negative electrode active material according to the present application; a negative electrode conductive material; and a negative electrode binder.

[0019] In another embodiment, there is provided an anode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode composition according to the present application or a cured product thereof.

[0020] Finally, a lithium secondary battery is provided, including: a cathode; an anode for a lithium secondary battery according to the present application; a separator provided between the cathode and the anode; and an electrolyte.

[0021] In the case of a negative electrode slurry containing a silicon-based active material, there is a risk of explosion due to the generation of hydrogen gas during manufacturing and storage, and the problem of reduced phase stability also occurs. Therefore, the negative electrode active material of the present invention is characterized by forming a coating layer having a thickness of Formula 1 relative to the average particle diameter of the silicon-based active material on the surface of the silicon-based active material.

[0022] As described above, by having a carbon coating layer having a thickness of Equation 1, the pH of the negative electrode active material itself can be controlled to be 5 or more and 9 or less, and the pH of the negative electrode active material affects the stability of the binder and slurry included in the negative electrode slurry, thereby reducing the amount of gas generated in the negative electrode slurry state, thereby reducing phase stability and the risk of explosion.

[0023] Figure 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application.

[0024] Figure 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application.

[0025] Figure 3 is a diagram showing a method for calculating the crystal grain size.

[0026] <Explanation of symbols>

[0027] 10: Negative current collector layer

[0028] 20: Negative active material layer

[0029] 30: Membrane

[0030] 40: Positive active material layer

[0031] 50: Positive current collector layer

[0032] 100: Cathode for lithium secondary batteries

[0033] 200: Cathode for lithium secondary batteries

[0034] Before explaining the present invention, some terms are first defined.

[0035] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0036] In this specification, ‘p to q’ means a range of ‘p or more and q or less.’

[0037] In this specification, "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0038] In this specification, "Dn" means particle size distribution, and means the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0039] In one embodiment of the present application, particle size or particle diameter may mean the average diameter or representative diameter of each grain forming the metal powder.

[0040] As used herein, the term "a polymer comprises a monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. As used herein, "a polymer comprises a monomer" is interpreted to mean that the polymer comprises the monomer as a monomer unit.

[0041] In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

[0042] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0043] Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0044] One embodiment of the present specification provides a negative electrode active material comprising a silicon-based active material; and a coating layer provided on the surface of the silicon-based active material; wherein the coating layer includes a carbon-based material, and the thickness of the coating layer satisfies the following formula 1.

[0045] [Formula 1]

[0046] Silicon-based active material average particle size (D50) / 70 < coating layer thickness < silicon-based active material average particle size (D50) / 10

[0047] In the case of a negative electrode slurry containing a silicon-based active material, there is a risk of explosion due to the generation of hydrogen gas during manufacturing and storage, and the problem of reduced phase stability also occurs. Therefore, the negative electrode active material of the present invention is characterized by forming a coating layer having a thickness of Formula 1 relative to the average particle diameter of the silicon-based active material on the surface of the silicon-based active material.

[0048] Below, a more specific description of the negative active material is disclosed.

[0049] In the present application, the silicon-based active material is SiOx (x=0), SiOx (0 <x<2), Si / C, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함하는 것인 음극 활물질을 제공한다.

[0050] That is, the present application is intended to solve the problem of using a silicon-based active material with high efficiency and capacity, and any silicon-based active material used in the art can be used without limitation.

[0051] In the present application, Si / C is a silicon-carbon composite, and is different from silicon carbide, which is SiC. That is, silicon carbide is a material that cannot function as an active material, and when the heat treatment temperature exceeds a certain range in the process of forming a coating layer on the Si / C surface, SiC (silicon carbide) is formed, and there is a difference between SiC and the negative active material of the present invention (silicon-based active material + coating layer). That is, in the present application, when the silicon-based active material has Si / C and a coating layer, it is a case where a coating layer is formed on the surface of the silicon-carbon composite, and there is a difference from the case of SiC (silicon carbide).

[0052] In one embodiment of the present application, the silicon-based active material is SiOx (x=0) and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 실리콘계 활물질 100 중량부 기준 상기 SiOx (x=0)를 70 중량부 이상 포함할 수 있다.

[0053] In one embodiment of the present application, the silicon-based active material includes SiOx (x=0), and may include 70 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[0054] 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, of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0055] In one embodiment of the present application, the silicon-based active material may be used as a silicon-based active material, particularly one including pure silicon (Si) particles. Using pure silicon (Si) particles as the silicon-based active material may mean that, based on 100 parts by weight of the total silicon-based active material, the silicon-based active material includes pure Si particles (SiOx (x=0)) that are not combined with other particles or elements within the above range.

[0056] In one embodiment of the present application, the silicon-based active material may be formed of silicon-based particles having 100 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[0057] In one embodiment of the present application, the silicon-based active material may include a metal impurity, and in this case, the impurity may be a metal that may be generally included in the silicon-based active material, and specifically may include 0.1 part by weight or less based on 100 parts by weight of the silicon-based active material.

[0058] In the case of silicon-based active materials, compared to the existing graphite-based active materials, the capacity is significantly higher, so attempts to apply it are increasing. However, because the volume expansion rate is high during the charge / discharge process, it is limited to cases where a small amount is mixed with the graphite-based active material and used.

[0059] Therefore, in the case of the present invention, in order to improve capacity performance, only a silicon-based active material is used as an anode active material, and in order to solve the above-mentioned problem, the existing problem is solved by controlling the crystal grain size or surface area of ​​the silicon-based active material itself rather than controlling the composition of the conductive agent and binder.

[0060] In one embodiment of the present application, the crystal grain size of the silicon-based active material may be 200 nm or less.

[0061] In another embodiment, the crystal grain size of the silicon-based active material may be 200 nm or less, preferably 130 nm or less, more preferably 110 nm or less, even more preferably 100 nm or less, specifically 95 nm or less, and even more specifically 91 nm or less. The crystal grain size of the silicon-based active material may have a range of 10 nm or more, preferably 15 nm or more.

[0062] The above silicon-based active material has the above crystal grain size, and the crystal grain size of the silicon-based active material can be controlled by changing the process conditions in the manufacturing process. At this time, by satisfying the above range and ensuring that the grain boundaries are widely distributed, when lithium ions are inserted, they are inserted uniformly, thereby reducing the stress applied when lithium ions are inserted into silicon particles, and thus alleviating particle breakage. As a result, it has the characteristic of improving the life stability of the negative electrode. When the crystal grain size exceeds the above range, the grain boundaries within the particles become narrowly distributed, and in this case, lithium ions within the particles are inserted unevenly, so that the stress due to ion insertion is large, resulting in particle breakage.

[0063] In one embodiment of the present application, the silicon-based active material includes a crystal structure having a crystal grain distribution of 1 nm or more and 200 nm or less, and an anode active material is provided in which the area ratio of the crystal structure is 5% or less based on the total area of ​​the silicon-based active material.

[0064] In another embodiment, the area ratio of the crystal structure based on the total area of ​​the silicon-based active material may be 5% or less, 3% or less, or 0.1% or more.

[0065] That is, the silicon-based active material according to the present application has a crystal grain size of 200 nm or less, so that a single crystal structure can be formed with a small size and satisfy the above-mentioned area ratio. Accordingly, the distribution of grain boundaries can be broadened, and thus the aforementioned effects can be exhibited.

[0066] In one embodiment of the present application, a negative electrode active material is provided in which the number of crystal structures included in the silicon-based active material is 20 or more.

[0067] In another embodiment, the number of crystal structures included in the silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may satisfy a range of 60 or less, or 50 or less.

[0068] That is, as described above, when the silicon-based active material has a crystal grain size that satisfies the above range and the number of crystal structures that satisfies the above range, the strength of the silicon-based active material itself has an appropriate range, so that when included in an electrode, it can provide flexibility and also has the characteristic of efficiently suppressing volume expansion.

[0069] In the present application, a crystal grain means a crystal particle that is a collection of irregularly shaped microscopic particles in a metal or material, and the crystal grain size may refer to the diameter of an observed crystal grain. That is, in the present application, the crystal grain size refers to the size of a domain that shares the same crystal direction within a particle, and is a different concept from the particle size or particle diameter that expresses the size of a material.

[0070] In one embodiment of the present application, the crystal grain size can be calculated as the FWHM (Full Width at Half Maximum) value through XRD analysis. Specifically, the method for calculating the crystal grain size can be seen in FIG. 3. In FIG. 3, the remaining values ​​excluding L are measured through XRD analysis of a silicon-based active material, and the crystal grain size can be measured through the Debey-Scherrer equation, which shows that the FWHM and the crystal grain size are inversely proportional. In this case, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[0071] [Formula 1-1]

[0072] FWHM=Kλ / LCosθ

[0073] In the above formula 1-1,

[0074] L represents the grain size, K is a constant, θ is the bragg angle, and λ is the wavelength of the X-ray.

[0075] In addition, the shape of the crystal grains is diverse and can be measured three-dimensionally, and the size of the crystal grains can generally be measured using the commonly used circle method and diameter measurement method, but is not limited thereto.

[0076] The above diameter measurement method can be measured by drawing 5-10 equilibrium lines, each of which is L mm long, on a microscopic photograph of the target particle, counting the number of grains z on the lines, and averaging them. At this time, only those that are completely included are counted, and those that cross are excluded. If the number of lines is P and the magnification is V, the average grain diameter can be calculated using the following equations 1-2.

[0077] [Formula 1-2]

[0078] Dm = (L*P*10 3 ) / (zV) (um)

[0079] In addition, the above circle method is a method of calculating the average area of ​​crystal grains by drawing a circle of a set diameter on a microscopic photograph of the target particle and calculating the number of crystal grains within the circle and the number of crystal grains that fall on the boundary line using the following equation 1-3.

[0080] [Formula 1-3]

[0081] Fm = (Fk * 10 6 ) / ((0.67n + z) V 2 )(um 2 )

[0082] In the above equation 1-2, Fm represents the average particle area, Fk represents the measured area on the photograph, z represents the number of particles inside the circle, n represents the number of particles in the circular arc, and V represents the magnification of the microscope.

[0083] In one embodiment of the present application, the silicon-based active material may include silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

[0084] The above-mentioned silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, which means that it includes a plurality of individual silicon-based particles having particle sizes within the above range, and the number of silicon-based particles included is not limited.

[0085] The particle size of the above silicon-based particles can be expressed by their diameter if they are spherical, but even if they are of a shape other than spherical, the particle size can be measured by comparing them to the spherical case, and the particle size of individual silicon-based particles can be measured by a method generally used in the art.

[0086] In the present application, a negative electrode active material is provided in which the average particle diameter (D50) of the silicon-based active material is 1 μm or more and 10 μm or less.

[0087] Meanwhile, the average particle diameter (D50 particle size) of the silicon-based active material of the present invention may be 1 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle diameter is within the above range, the specific surface area of ​​the particles is within an appropriate range, so that the viscosity of the negative electrode slurry is formed within an appropriate range. Accordingly, the particles constituting the negative electrode slurry are smoothly dispersed. In addition, when the size of the silicon-based active material is greater than or equal to the lower limit, the contact area between the silicon particles and the conductive material is excellent due to the composite composed of the conductive material and the binder in the negative electrode slurry, so that the possibility of the conductive network continuing increases, thereby increasing the capacity retention rate. Meanwhile, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded, so that the surface of the negative electrode is formed smoothly, and thus the phenomenon of uneven current density during charge and discharge can be prevented.

[0088] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET 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 m 2 / g. BET surface area is measured according to DIN 66131 (using nitrogen).

[0089] In one embodiment of the present application, the silicon-based active material may exist in a crystalline or amorphous form, for example, and is preferably non-porous. The silicon particles are preferably spherical or fragment-shaped. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0090] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape and its sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0091] In the present application, the circularity is determined by the following equation 3-1, where A is the area and P is the boundary line.

[0092] [Formula 3-1]

[0093] 4πA / P 2

[0094] The negative active material according to the present application includes a coating layer surrounding at least a portion of the surface of a silicon-based active material, whereby the coating layer acts as a protective layer, thereby preventing a hydrogen generation reaction by suppressing the reaction between the surface of the silicon-based active material and a solvent when forming a slurry, thereby improving uneven electrode coating caused by bubble generation during electrode coating.

[0095] In one embodiment of the present application, the thickness of the coating layer can satisfy the range of Equation 1.

[0096] In the case of the negative electrode active material according to the present application, the thickness of the coating layer is not simply selected as a range, but the thickness of the coating layer is adjusted relative to the average particle diameter (D50) of the silicon-based active material, and accordingly, the pH of the negative electrode active material is suitably selected, thereby having the characteristic of solving the aforementioned problem when stored in a slurry.

[0097] That is, the pH of the negative electrode active material is related to both the thickness of the coating layer and the thickness of the silicon-based active material, and is affected by the degree of exposure of the silicon-based active material due to the thickness of the coating layer and the difference in specific surface area due to the D50 of the silicon-based active material. When the relationship of the above-mentioned equation 1 is satisfied, the pH of the negative electrode active material itself is formed appropriately.

[0098] If the thickness of the coating layer satisfies the above range, contact between the solvent and the silicon-based active material can be easily prevented, and also, by having the above thickness range, electrical conductivity can be improved, and the content of the silicon-based active material can be maximized, so that the capacity characteristics also have excellent characteristics. That is, if it is below the range of the above formula 1, it is difficult to limit gas generation, and if it exceeds the above range, the capacity and efficiency of the active material may decrease, so it is preferable to select within the above range.

[0099] In one embodiment of the present application, a negative electrode active material is provided, wherein the electrical conductivity of the coating layer is 100 mS / m or more and 1,000 mS / m or less.

[0100] In this application, electrical conductivity refers to the ability of a material itself to allow current to flow when an electric field is applied, and can be used as a parameter expressing the degree to which current flows well within a material.

[0101] The above electrical conductivity can be measured using a general measurement method used in the art, and the reciprocal of the electrical conductivity can mean resistivity, which can have different values ​​depending on the type and composition of the material.

[0102] In one embodiment of the present application, the electrical conductivity of the coating layer may be 100 mS / m or more and 1,000 mS / m or less, preferably 120 mS / m or more and 900 mS / m or less, and more preferably 180 mS / m or more and 800 mS / m or less.

[0103] The coating layer according to the present application suppresses the reaction between the silicon-based active material and the slurry solvent as described above, and at the same time has high electrical conductivity as described above, and is formed on the surface of the silicon-based active material to lower the resistance of the negative electrode active material itself, thereby improving the life stability through a reduction in electrode resistance due to an improvement in the electrical conductivity of the active material.

[0104] In one embodiment of the present application, a negative electrode active material is provided in which the coating layer has an area of ​​arrangement of 90% or more based on the outer surface of the silicon-based active material.

[0105] The above-mentioned placement area may refer to the extent to which the coating layer is coated based on the outer surface of the silicon-based active material. That is, when the coating layer completely surrounds the silicon-based active material, the placement area may be 100%, and in this case, the surface of the silicon-based active material may be isolated from the outside, i.e., isolated by the coating layer.

[0106] In one embodiment of the present application, the area of ​​the coating layer may be 90% or more, 91% or more, or 92% or more based on the outer surface of the silicon-based active material, and may satisfy a range of 100% or less, 99% or less, or 95% or less.

[0107] By having the above-mentioned coating layer arrangement area, it has the characteristic of being able to suppress gas generation more easily, and easily performing the role of a silicon-based active material when included in an electrode later. In particular, the coating layer according to the present application is used to see the effect of suppressing gas generation, and when the arrangement area of ​​the carbon coating layer is 100%, it has the characteristic of being able to reduce gas generation by blocking contact with water in a slurry state.

[0108] In one embodiment of the present application, a negative electrode active material is provided, wherein the carbon-based material in the coating layer includes at least one selected from the group consisting of crystalline carbon and amorphous carbon.

[0109] In one embodiment of the present application, the carbon coating layer includes crystalline carbon.

[0110] In one embodiment of the present application, the carbon coating layer includes amorphous carbon.

[0111] In one embodiment of the present application, the coating layer includes a carbon-based material, and the carbon-based material provides a negative active material including carbon having an ID / IG of 0.1 to 1.2 when measured by Raman spectroscopy.

[0112] In another embodiment, ID / IG can satisfy a range of 0.1 to 1.2, preferably 0.13 to 1.2.

[0113] The above ID / IG may refer to an index for identifying defects in a carbon structure, and may refer to an index for measuring the degree of defects present in a carbon material through Raman spectroscopy measurement.

[0114] By including carbon that satisfies the above raman spectroscopy range, it has the characteristic of excellent life performance when the battery is operated in the future.

[0115] In the present application, a negative electrode active material is provided, wherein the carbon-based material in the coating layer includes at least one selected from the group consisting of graphene; carbon; and graphite.

[0116] In one embodiment of the present application, a negative electrode composition is provided, including the negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0117] In one embodiment of the present application, a negative electrode composition is provided in which the negative electrode active material is at least 40 parts by weight based on 100 parts by weight of the negative electrode composition.

[0118] In another embodiment, the negative electrode active material may be included in an amount of 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and even 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, and even more preferably 85 parts by weight or less.

[0119] The negative electrode composition according to the present application uses a negative electrode active material that satisfies a specific crystal grain size capable of controlling the volume expansion rate during the charge and discharge process even when a silicon-based active material with a significantly high capacity is used within the above range, so that the performance of the negative electrode is not deteriorated even within the above range, and has the characteristic of excellent output characteristics during charge and discharge.

[0120] Previously, graphite compounds were typically used solely as negative electrode active materials. However, with the increasing demand for high-capacity batteries, attempts to mix silicon-based active materials to increase capacity have been increasing. However, even if the properties of silicon-based active materials themselves are adjusted as described above, the rapid expansion of volume during the charge / discharge process can cause some problems, damaging the conductive path formed within the negative electrode active material layer.

[0121] Therefore, in one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0122] In one embodiment of the present application, the dot-shaped conductive material may be used to improve conductivity of the negative electrode, and refers to a dot-shaped or spherical conductive material having conductivity without causing chemical change. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of implementing high conductivity and excellent dispersibility.

[0123] In one embodiment of the present application, the dot-shaped conductive material has a BET specific surface area of ​​40 m 2 / g or more than 70m 2 / g or less, preferably 45m 2 / g or more than 65m 2 / g or less, more preferably 50m 2 / g or more than 60m 2 / g can be less.

[0124] In one embodiment of the present application, the dot-shaped conductive material can satisfy a volatile matter 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.

[0125] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, the functional groups present on the surface of the dot-shaped conductive material exist, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed within the solvent. In particular, in the present invention, the functional group content of the dot-shaped conductive material can be reduced by using a specific silicon-based active material, thereby having an excellent effect in improving dispersibility.

[0126] In one embodiment of the present application, it is characterized by including a dot-shaped conductive material having a functional group content within the above range together with a silicon-based active material, and the functional group content can be controlled by adjusting the degree of heat treatment of the dot-shaped conductive material.

[0127] In one embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0128] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0129] The above-mentioned planar conductive material can improve conductivity by increasing planar contact between silicon particles within the cathode, and at the same time, suppress the disconnection of conductive paths due to volume expansion. The above-mentioned planar conductive material can be expressed as a plate-shaped conductive material or a bulk conductive material.

[0130] In one embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0131] In one embodiment of the present application, the average particle diameter (D50) of the surface-shaped conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the above range is satisfied, dispersion is easy without causing excessive viscosity increase of the negative electrode slurry due to sufficient particle size. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0132] In one embodiment of the present application, the surface-shaped conductive material provides a negative electrode composition having 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.

[0133] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material having a high BET surface area; or a low-specific surface area planar conductive material.

[0134] In one embodiment of the present application, a high surface area surface conductive material or a low surface area surface conductive material may be used without limitation as the surface conductive material, but in particular, since the surface conductive material according to the present application may be affected to some extent by dispersion in electrode performance, it may be particularly preferable to use a low surface area surface conductive material that does not cause dispersion problems.

[0135] In one embodiment of the present application, the surface-shaped conductive material has a BET specific surface area of ​​1 m 2 / g can be more than that.

[0136] In another embodiment, the surface-shaped conductive material has a BET surface area of ​​1 m 2 / g or more than 500m 2 / g or less, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more than 250m 2 / g can be less.

[0137] The planar conductive material according to the present application may be a planar conductive material with a high specific surface area; or a planar conductive material with a low specific surface area.

[0138] In another embodiment, the surface-shaped conductive material is a high surface area surface-shaped conductive material, and has a BET surface area of ​​50 m 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 / g can satisfy the range below.

[0139] In another embodiment, the surface-shaped conductive material is a low surface area surface-shaped conductive material, and has a BET surface area of ​​1 m 2 / g or more than 40m 2 / g or less, preferably 5m 2 / g or more than 30m 2 / g or less, more preferably 5m 2 / g or more than 25m 2 / g can satisfy the range below.

[0140] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope, in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in parallel or entangled with their longitudinal axes in the carbon nanotube unit direction, unless otherwise specified. The carbon nanotube units have a cylindrical shape of a graphite sheet with a nano-sized diameter and an sp2 bonding structure. At this time, the graphite sheets may exhibit conductor or semiconductor properties depending on the curling angle and structure. The above bundled carbon nanotubes can be uniformly dispersed during the manufacture of a cathode compared to entangled type carbon nanotubes, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0141] In the present application, a negative electrode composition is provided in which the negative electrode conductive material includes at least a linear conductive material.

[0142] In one embodiment of the present application, a negative electrode composition is provided in which the negative electrode conductive material is 10 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0143] In another embodiment, the negative electrode conductive material may be included in an amount of 0.1 to 10 parts by weight, preferably 0.2 to 9 parts by weight, more preferably 0.4 to 8 parts by weight, and most preferably 0.4 to 8 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0144] In one embodiment of the present application, a negative electrode composition is provided, wherein the negative electrode conductive material includes a planar conductive material and a linear conductive material.

[0145] In one embodiment of the present application, the negative electrode composition is provided, wherein the negative electrode conductive material comprises 80 parts by weight or more and 99.99 parts by weight or less of the planar conductive material based on 100 parts by weight of the negative electrode conductive material; and 0.01 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0146] In another embodiment, the negative electrode conductive material may include 80 parts by weight or more and 99.99 parts by weight or less of the planar conductive material, preferably 85 parts by weight or more and 99.99 parts by weight or less, and more preferably 95 parts by weight or more and 99.95 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0147] In another embodiment, the negative electrode conductive material may include 0.01 to 20 parts by weight of the linear conductive material, preferably 0.01 to 15 parts by weight, and more preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0148] In one embodiment of the present application, since the negative electrode conductive material includes a planar conductive material and a linear conductive material and satisfies the above composition and ratio, it does not have a significant effect on the life characteristics of an existing lithium secondary battery, and in particular, when the planar conductive material and the linear conductive material are included, 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 high-temperature gas generation.

[0149] In one embodiment of the present application, the cathode conductive material may be formed of a linear conductive material.

[0150] In particular, when a linear conductive material is used alone, the electrode tortuosity, which is a problem of silicon-based negative electrodes, can be simplified, thereby improving the electrode structure and thus reducing the resistance to movement of lithium ions within the electrode.

[0151] In one embodiment of the present application, when the negative electrode conductive material comprises a linear conductive material alone, the negative electrode conductive material may comprise 0.05 parts by weight or more and 5 parts by weight or less, preferably 0.1 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.

[0152] The negative electrode conductive material according to the present application has a completely separate composition from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact between silicon-based active materials, which undergo a significant volume expansion of the electrode due to charging and discharging, and the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in composition and role from the negative electrode conductive material of the present invention.

[0153] In addition, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different composition from the conductive material applied to a graphite-based active material. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity, and is completely different in composition and role from the negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0154] In one embodiment of the present application, the planar conductive material used as the aforementioned negative electrode conductive material has a structure and function different from those of carbon-based active materials generally used as negative electrode active materials. 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 processed into a spherical or dot-shaped form to facilitate the storage and release of lithium ions.

[0155] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and can be expressed as plate-like graphite. In other words, it refers to a material included to maintain a conductive path within the negative electrode active material layer, and is not a material that plays a role in storing and releasing lithium, but rather a material that secures a conductive path in a planar shape within the negative electrode active material layer.

[0156] That is, in the present application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-shaped form and used as a material that secures a conductive path rather than a role for storing or releasing lithium. In this case, the included negative electrode active material has high capacity characteristics for lithium storage and release, and serves to store and release all lithium ions delivered from the positive electrode.

[0157] On the other hand, in the present application, the use of a carbon-based active material as an active material means that it is processed into a dot or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0158] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is in a dot-like shape and has a BET specific surface area of ​​0.1 m 2 / g or more than 4.5 m 2 / g or less can be satisfied. In addition, the plate-shaped graphite, which is a planar conductive material, has a BET surface area of ​​5 m in the form of a planar surface. 2 / g can be more than that.

[0159] 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, polyacrylamide, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (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 a material in which hydrogens thereof are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof. May include.

[0160] The negative electrode binder according to one embodiment of the present application serves to hold the active material and conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. If the above-mentioned role is satisfied, all general binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0161] In one embodiment of the present application, the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and may be 3 parts 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.

[0162] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, including: a negative electrode current collector layer; and a negative electrode active material layer including a negative electrode composition according to the present application or a cured product thereof formed on one or both sides of the negative electrode current collector layer.

[0163] FIG. 1 is a diagram showing a laminated structure of an anode for 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 surface of an anode current collector layer (10) can be confirmed, and FIG. 4 shows that the anode active material layer is formed on one surface, but it can be included on both surfaces of the anode current collector layer.

[0164] In one embodiment of the present application, the negative electrode for the lithium secondary battery can be formed by applying and drying a negative electrode slurry containing the negative electrode composition to one or both sides of a negative electrode current collector layer.

[0165] At this time, the cathode slurry may include the cathode composition described above; and a slurry solvent.

[0166] In one embodiment of the present application, the solid content of the cathode slurry can satisfy 5% or more and 60% or less.

[0167] In another embodiment, the solid content of the cathode slurry can satisfy a range of 5% or more and 60% or less, preferably 10% or more and 58% or less, and more preferably 15% or more and 55% or less.

[0168] The solid content of the above cathode slurry may mean the content of the cathode composition included in the cathode slurry, and may mean the content of the cathode composition based on 100 parts by weight of the cathode slurry.

[0169] When the solid content of the above negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode composition, and thus has the characteristic of efficiently forming the negative electrode active material layer.

[0170] In one embodiment of the present application, the slurry solvent can be used without limitation as long as it can dissolve the negative electrode composition, and specifically, water or NMP can be used.

[0171] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. The negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0172] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

[0173] However, the thickness can be varied depending on the type and purpose of the cathode used and is not limited thereto.

[0174] In one embodiment of the present application, the porosity of the negative electrode active material layer can satisfy a range of 10% or more and 60% or less.

[0175] In another embodiment, the porosity of the negative electrode active material layer can satisfy a 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.

[0176] The above porosity varies depending on the composition and content of the silicon-based active material; conductive material; and binder included in the negative electrode active material layer, and in particular, the silicon-based active material and conductive material according to the present application are included in a specific composition and content portion to satisfy the above range, and accordingly, the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

[0177] In one embodiment of the present application, a lithium secondary battery is provided, including: a positive electrode; an anode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0178] FIG. 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 negative electrode (100) including a negative electrode active material layer (20) on one surface of a negative electrode current collector layer (10) can be confirmed, and a lithium secondary battery positive electrode (200) including a positive electrode active material layer (40) on one surface of a positive electrode current collector layer (50) can be confirmed, and it is shown that the lithium secondary battery negative electrode (100) and the lithium secondary battery positive electrode (200) are formed in a laminated structure with a separator (30) interposed therebetween.

[0179] A secondary battery according to one embodiment of the present specification may particularly include the negative electrode for a lithium secondary battery as described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is identical to the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof will be omitted.

[0180] The above 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.

[0181] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and 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. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0182] The above 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), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxide represented by O2 (wherein, 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 (wherein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0183] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0184] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0185] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0186] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0187] Examples of the above electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0188] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0189] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0190] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0191] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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 may be used.

[0192] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine 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 battery capacity decrease, and improving the discharge capacity of the battery.

[0193] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus can 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.

[0194] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0195] <Manufacturing Example>

[0196] <Preparation of negative active material of Example 1>

[0197] 100 g of powder mixed with Si and SiO2 in a molar ratio of 1:1 and 6 g of Mg were mixed in a reactor and heated at 1500°C in a vacuum. Thereafter, the vaporized Si, SiO2, and Mg mixture gas was reacted in a cooling zone in a vacuum with a cooling temperature of 850°C to condense into a solid phase.

[0198] The above silicon-based active material was pulverized using a ball mill to produce silicon-based particles of 5 microns in size. Thereafter, Mg-doped SiOx particles were produced by heat treatment at a temperature of 850°C in an inert atmosphere.

[0199] Afterwards, the silicon composite particles were placed in the hot zone of the CVD device while maintaining an inert atmosphere by flowing Ar gas, and heat treatment was performed by blowing propane gas into the hot zone at 950°C so that the carbon thickness became 0.15 microns.

[0200] <Preparation of negative active material of Example 2>

[0201] It was manufactured in the same manner as Example 1 above, except that the heat treatment time of propane gas was adjusted so that the carbon thickness became 0.35 microns in the final step.

[0202] <Preparation of negative active material of Example 3>

[0203] Specific surface area 1850~1900 m 2 / g, pore volume 0.80~0.85cm 3 / g, 10 g of an amorphous porous carbon scaffold with a particle size of 6 microns was placed in a ceramic crucible and placed in the center of a horizontal tube furnace. After sealing the furnace and purging with Ar gas, the furnace temperature was increased to 500°C at 10°C / min, and silane gas and hydrogen gas were maintained for 60 to 90 minutes with different flow rates. In addition, the furnace temperature was increased to 900°C, and propane gas was maintained to perform heat treatment until the carbon thickness became 0.3 microns.

[0204] <Manufacturing of negative active material of comparative example 1>

[0205] It was manufactured in the same manner as Example 1 except that the carbon coating step was not performed in the last step.

[0206] <Manufacturing of negative active material in Comparative Example 2>

[0207] In the above Example 2, it was manufactured in the same manner as above except that the heat treatment time of propane gas was adjusted so that the thickness of the carbon became 0.8 microns in the final step.

[0208] <Manufacturing of negative active material in Comparative Example 3>

[0209] In the above Example 3, it was manufactured in the same manner except that the heat treatment time of propane gas was adjusted so that the thickness of the carbon became 1 micron in the final step.

[0210] The properties of the negative active materials manufactured in the above examples and comparative examples were as follows.

[0211] Silicon-based active material average particle size (D50, micron) Thickness of coating layer Formula 1 Range Negative active material pH Example 15.2 0.15 micron 0.1 < Formula 1 < 0.5 2 7.6 Example 25.3 0.35 micron 0.1 < Formula 1 < 0.5 3 7.3 Example 36.3 0.3 micron 0.12 < Formula 1 < 0.6 3 6.6 Comparative example 15--9.8 Comparative example 25.8 0.8 micron 0.11 < Formula 1 < 0.5 8 7.1 Comparative example 371 micron 0.14 < Formula 1 < 0.7 6.8

[0212] <Manufacturing of the cathode>

[0213] Binder synthesis

[0214] In a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet pipe, acrylamide, acrylic acid, and acrylonitrile were mixed in a weight ratio of 60:30:10, a polymerization initiator (ammonium persulfate) was added, and the mixture was reacted at 75°C for 6 hours to produce a binder in an aqueous solution state.

[0215] Next, a (meth)acrylic binder was prepared by neutralizing with an aqueous NaOH solution.

[0216] Preparation of cathode slurry

[0217] As the negative active material, the negative active material manufactured in the above examples and comparative examples was used, and as the conductive material, two types of particle-type conductive material (SFG6L, Graphite) and SWCNT (product name: Tuball OCSiAl) were used, and the aqueous binder synthesized above was used. At this time, the negative electrode composition was prepared by mixing the negative active material: particle-type conductive material: SWCNT: aqueous binder in a weight ratio of 80:9.6:0.8:9.6.

[0218] A cathode slurry was prepared by adding water as a solvent, wherein the water content was adjusted in consideration of coating properties, viscosity, and solid content, and the viscosity of the obtained cathode slurry was adjusted to be 8000 cps.

[0219] Battery Manufacturing

[0220] The above-mentioned negative electrode slurry was coated on a copper foil having a thickness of 18 μm and dried, and an electrode active material layer having a thickness of 50 μm was formed on one side of the copper foil, and a test electrode (negative electrode) was manufactured by punching it into a circle having a diameter of 14 mm.

[0221] A metal lithium foil with a thickness of 0.33 mm was used as the positive electrode.

[0222] A porous polyethylene sheet with a thickness of 0.1 mm was used as a separator. In addition, as an electrolyte, LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:1, as a lithium salt, at a concentration of approximately 1 mol / L.

[0223] The above cathode, anode, separator, and electrolyte were sealed in a stainless steel container to manufacture a coin cell for evaluation with a thickness of 2 mm and a diameter of 32 mm.

[0224] Experimental Example 1: Measurement of phase stability (viscosity change) of cathode slurry

[0225] 5 g of the negative active material or the negative slurry was placed in a 9 cm x 9 cm pouch, sealed, and stored in a constant temperature chamber at a high temperature (60°C) for 24 hours. The gas inside the pouch was captured and the amount generated was measured using GC / MS. The evaluation results are shown in Table 2 below.

[0226] Experimental Example 2: Battery Characteristics Evaluation

[0227] The coin cell manufactured above was charged at a constant current of 0.05 C until the voltage became 0.01 V, discharged at a constant current of 0.05 C until the voltage became 1.0 V, and the discharge capacity was obtained. The above process was repeated 100 cycles to calculate the capacity retention rate, and the results are shown in Table 2 below.

[0228] Slurry phase stability (H2 gas generation, μL) Initial discharge capacity (mAh / g) Capacity retention rate (%) Example 16120081 Example 25130080 Example 39175087 Comparative example 112000125076 Comparative example 25105073 Comparative example 310145082

[0229] As can be seen in Tables 1 and 2 above, the negative active materials of Examples 1 to 3 of the present invention formed a coating layer having a thickness of Formula 1 relative to the average particle diameter of the silicon-based active material on the surface of the silicon-based active material.

[0230] As described above, by having a carbon coating layer having a thickness within the range of Equation 1, the pH of the negative electrode active material itself can be controlled to 5 or more and 9 or less, and it was confirmed that the pH of the negative electrode active material affects the stability of the binder and slurry included in the negative electrode slurry, thereby reducing the amount of gas generated in the negative electrode slurry state, and thus reducing the phase stability and risk of explosion.

[0231] In the case of Comparative Example 1, in which a coating layer was not formed, it was confirmed that the phase stability was reduced due to a large amount of hydrogen gas generated in the slurry phase safety evaluation.

[0232] In the case of Comparative Example 2, when the coating layer was formed beyond the range of Equation 1 of the present application, it was confirmed that the formation of the coating layer suppressed the generation of hydrogen gas in the slurry, but it was confirmed that the initial discharge capacity and the capacity retention rate during charge and discharge decreased.

[0233] In the case of Comparative Example 3, this corresponds to a case where the coating layer exceeds the range of Equation 1. That is, it can be confirmed that the generation of hydrogen gas in the slurry is suppressed by forming the coating layer above a certain range, but it can be confirmed that the initial discharge capacity and the capacity retention rate during charge and discharge decrease.

Claims

1. A negative electrode active material comprising a silicon-based active material; and a coating layer provided on the surface of the silicon-based active material; The above coating layer contains a carbon-based material, The thickness of the above coating layer satisfies the following equation 1: [Formula 1] Silicon active material average particle size (D50) / 70 < Thickness of coating layer < Silicon active material average particle size (D50) / 10 2. In claim 1, The above silicon-based active material is SiOx (x=0), SiOx (0 <x<2), Si / C, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함하는 것인 음극 활물질.

3. In claim 1, The above silicon-based active materials are SiOx (x=0) and SiOx (0 <x<2)로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 실리콘계 활물질 100 중량부 기준 상기 SiOx (x=0)는 70 중량부 이상 포함하는 것인 음극 활물질.

4. In claim 1, A negative electrode active material, wherein the average particle diameter (D50) of the above silicon-based active material is 1 μm or more and 10 μm or less.

5. In claim 1, A negative electrode active material, wherein the crystal grain size of the silicon-based active material is 200 nm or less.

6. In claim 1, A negative electrode active material, wherein the carbon-based material in the coating layer includes at least one selected from the group consisting of crystalline carbon; and amorphous carbon.

7. In claim 1, A negative electrode active material in which the carbon-based material in the coating layer includes at least one selected from the group consisting of graphene; carbon; and graphite.

8. A negative electrode composition comprising a negative electrode active material according to any one of claims 1 to 7; a negative electrode conductive material; and a negative electrode binder.

9. In claim 8, A negative electrode composition wherein the negative electrode active material is at least 40 parts by weight based on 100 parts by weight of the negative electrode composition.

10. In claim 8, A cathode composition wherein the cathode conductive material comprises at least a linear conductive material.

11. In claim 8, A cathode composition wherein the cathode conductive material is present in an amount of 10 parts by weight or less based on 100 parts by weight of the cathode composition.

12. A negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, A negative electrode for a lithium secondary battery, wherein the negative electrode active material layer comprises the negative electrode composition according to claim 8 or a cured product thereof.

13. In claim 12, The thickness of the above negative electrode current collector layer is 1 μm or more and 100 μm or less, A negative electrode for a lithium secondary battery, wherein the thickness of the negative active material layer is 5 μm or more and 500 μm or less.

14. Bipolar; A negative electrode for a lithium secondary battery according to claim 12; A separator provided between the anode and the cathode; and A lithium secondary battery comprising an electrolyte.

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