Anode for lithium secondary battery, method for manufacturing anode for lithium secondary battery, and lithium secondary battery including anode

Abstract

The present application relates to a negative electrode for a lithium secondary battery, a method for producing 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. 10-2022-0113647 filed with the Korean Intellectual Property Office on September 7, 2022, and Korean Patent Application No. 10-2023-0117635 filed with the Korean Intellectual Property Office on September 5, 2023, the entire contents of which are incorporated herein by reference.

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

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

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

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

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

[0007] In recent years, in response to the demand for high-density energy batteries, active research has been conducted into methods for increasing capacity by using silicon-based compounds such as Si / C and SiOx as anode active materials, which have capacities more than 10 times greater than graphite-based materials. However, while silicon-based compounds, which are high-capacity materials, have superior capacity characteristics compared to conventionally used graphite, they rapidly expand in volume during charging, disrupting the conductive path and reducing battery performance, resulting in a drop in capacity from the start. Furthermore, with silicon-based anodes, lithium ions are not uniformly charged throughout the anode depth during repeated charge and discharge cycles, and reactions occur on the surface, accelerating surface degradation. Therefore, improvements are needed in terms of battery cycle performance.

[0008] As mentioned above, silicon-based active materials have significantly higher capacity than graphite, which is the most commonly used material in lithium secondary batteries. However, due to the above-mentioned issues, the SEI layer is continuously destroyed and regenerated. This requires the use of more electrolyte for the SEI layer regeneration, which in turn generates a large amount of gas. When gas is generated, the electrolyte separates the electrode and the separator, trapping the gas, widening the distance between the positive and negative electrodes and resulting in increased local resistance and a rapid reduction in battery life.

[0009] Therefore, various methods are being discussed to solve the above problems when using silicon-based compounds as negative electrode active materials, such as controlling the driving potential, coating an additional thin film on the active material layer, controlling the particle size of the silicon-based compound, or developing a binder that suppresses the volume expansion of the silicon-based compound to prevent the conductive path from being broken. Research is also being conducted into improving the lifespan characteristics of silicon-based negative electrodes by limiting the proportion of silicon-based active material used during initial charge and discharge through a method of prelithiating the silicon-based active material layer, thereby providing a reservoir function.

[0010] However, this method has limitations in its applicability because it may actually degrade battery performance, and there are still limitations in the commercialization of negative electrode batteries with a high silicon-based compound content. In particular, as the proportion of silicon-based active material in the silicon-based active material layer increases, pre-lithiation tends to concentrate on the surface of the negative electrode, causing damage to the silicon-based active material on the surface side and resulting in non-uniform pre-lithiation, which causes problems in improving life characteristics.

[0011] Therefore, even when a silicon-based compound is used as an active material, research is needed to find a method for suppressing gas generation and solving the above-mentioned problems. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0013] The present application relates to a negative electrode for a lithium secondary battery that uses a silicon-based active material in the negative electrode, but is capable of sensing generated gases (CO2, H2) to suppress gas generation, which is a problem in the past, and is capable of improving the uniformity during pre-lithiation and improving the capacity characteristics and cycle performance of the lithium secondary battery; a method for manufacturing a negative electrode for a lithium secondary battery; and a lithium secondary battery including the negative electrode.

[0014] In order to solve the above problems, the negative electrode for a lithium secondary battery according to the present application solves the above problems by providing a specific ceramic layer on the negative electrode active material layer. [Means for solving the problem]

[0015] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a ceramic layer provided on the surface of the silicon-based negative electrode active material layer opposite the surface facing the negative electrode current collector layer; wherein the ceramic layer comprises a ceramic layer composition or a dried product thereof, the ceramic layer has a thickness of 0.5 μm or more and 10 μm or less, the ceramic layer composition includes a ceramic and a binder, and the ceramic layer composition contains 10 parts by weight or more and 50 parts by weight or less of BaTiO3, based on 100 parts by weight of the ceramic.

[0016] In yet another embodiment, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including the steps of: preparing a negative electrode current collector layer; applying a negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a negative electrode active material layer; and applying a ceramic layer composition to a surface of the negative electrode active material layer opposite to the surface facing the negative electrode current collector layer to form a ceramic layer, wherein the ceramic layer has a thickness of 0.5 μm to 10 μm, the ceramic layer composition includes a ceramic and a binder, and contains 10 parts by weight to 50 parts by weight of BaTiO3 per 100 parts by weight of the ceramic.

[0017] 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]

[0018] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery includes a silicon-based negative electrode active material layer and a ceramic layer having a specific composition and thickness on top of the silicon-based negative electrode active material layer, which contains a certain amount of BaTiO3 capable of gas sensing within the ceramic layer, thereby enabling the recovery of a portion of the gas generated in the silicon-based negative electrode and reducing the amount of gas generated.

[0019] By including the ceramic layer capable of suppressing gas generation as described above, it is possible to suppress an increase in resistance and lithium deposition that occurs when bubbles are generated between the electrode and the separator, causing separation and increasing the electrode distance. Furthermore, it can also provide some stability effects like the SRS layer of the separator, thereby further improving the stability of the battery.

[0020] In addition, the ceramic layer also reduces direct contact points between the silicon-based anode and lithium metal, thereby improving the charge / discharge uniformity of the silicon-based anode and improving performance.

[0021] Furthermore, by having a ceramic layer on the silicon-based negative electrode active material layer, the ceramic layer formed on the separator can be eliminated or minimized, and the thickness of the separator roll can be reduced, resulting in excellent process and cost advantages.

[0022] That is, the negative electrode for a lithium secondary battery according to the present application is characterized by incorporating a ceramic layer having a specific thickness and composition to obtain the advantages of an electrode using a high content of Si particles as a single-layer active material, while resolving the drawbacks of such an electrode, such as surface deterioration, uniformity during pre-lithiation, and life characteristics problems due to gas generation. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 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. DETAILED DESCRIPTION OF THE INVENTION

[0024] Before describing the present invention, some terms will first be defined.

[0025] 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.

[0026] In this specification, "p to q" means a range of "not less than p and not more than q."

[0027] 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 may mean the specific surface area measured by the above-mentioned measurement method.

[0028] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, particle size distribution can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size when the particles pass through a laser beam.

[0029] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0030] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as a "homopolymer."

[0031] 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.

[0032] The present invention may, however, be embodied in various different forms and should not be construed as limited to the following detailed description, although the present invention may be practiced in various different forms, and the present invention may be practiced in various different forms and should not be construed as limited to the following detailed description, although the present invention may be practiced in various different forms, such as without limitation ...

[0033] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a ceramic layer provided on the surface of the silicon-based negative electrode active material layer opposite the surface facing the negative electrode current collector layer; wherein the ceramic layer comprises a ceramic layer composition or a dried product thereof, the ceramic layer has a thickness of 0.5 μm or more and 10 μm or less, the ceramic layer composition includes a ceramic and a binder, and the ceramic layer composition contains 10 parts by weight or more and 50 parts by weight or less of BaTiO3, based on 100 parts by weight of the ceramic.

[0034] The negative electrode for a lithium secondary battery according to the present application is characterized by the introduction of a ceramic layer having a specific thickness and composition to obtain the advantages of an electrode using a high content of Si particles as a single layer active material, while resolving the disadvantages of such an electrode, such as surface deterioration, uniformity during pre-lithiation, and life characteristics associated with gas generation.

[0035] 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 and a ceramic layer 10 on one side of a negative electrode current collector layer 30. While FIG. 1 shows the negative electrode active material layer formed on one side, it may also be formed on both sides of the negative electrode current collector layer.

[0036] The negative electrode for a lithium secondary battery of the present invention will be described in more detail below.

[0037] The present application provides a negative electrode for a lithium secondary battery, including: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a ceramic layer provided on the surface of the silicon-based negative electrode active material layer opposite the surface facing the negative electrode current collector layer.

[0038] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc., can be used. Furthermore, the bonding strength of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and the negative electrode current collector layer can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0039] In one embodiment of the present application, the negative electrode current collector layer may have a thickness of 1 μm or more and 100 μm or less.

[0040] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0041] In one embodiment of the present application, the silicon-based negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition provides a negative electrode for a lithium secondary battery including at least one selected from the group consisting of a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0042] In one embodiment of the present application, the silicon-based active material may include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0043] In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and metal impurities, 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.

[0044] In another embodiment, the silicon-based active material includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x ≤ 2), 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.

[0045] In another embodiment, based on the silicon-based active material of 100 parts by weight, it may include 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more of the SiOx (x = 0), and may include 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0046] <0​​​​In one embodiment of the present application, the silicon-based active material may be composed of SiOx (x=0).

[0048] Silicon-based active materials have significantly higher capacities than conventionally used graphite-based active materials, and attempts to use them are increasing. However, because of their high volume expansion rate during charging and discharging, they are only used in small amounts by mixing with graphite-based active materials.

[0049] The anode active material layer according to the present application contains a silicon-based active material, specifically pure silicon particles containing 70 parts by weight or more of SiOx (x = 0). In this case, when the pure silicon particles are contained in a high content, excellent capacity characteristics are obtained. In order to solve the problem of reduced lifespan due to the resulting non-uniform surface reaction, the anode active material layer according to the present invention includes a ceramic layer.

[0050] In one embodiment of the present application, the crystal grain size of the silicon-based active material may be 200 nm or less.

[0051] 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 be 10 nm or more, preferably 15 nm or more.

[0052] The silicon-based active material has the above-described crystal grain size, and the crystal grain size of the silicon-based active material can be adjusted by changing the process conditions during the manufacturing process. By satisfying this range, the grain boundaries are widely distributed, allowing lithium ions to be inserted uniformly during insertion, reducing the stress exerted when lithium ions are inserted into silicon particles and thereby mitigating particle cracking. As a result, the negative electrode has the characteristic of improving its life stability. If the crystal grain size exceeds this range, the crystal grain boundaries within the particles are narrowly distributed, causing lithium ions to be inserted non-uniformly within the particles, resulting in large stress due to ion insertion and particle cracking.

[0053] In one embodiment of the present application, the silicon-based active material may include a crystalline structure having a crystal grain distribution of 1 nm or more and 200 nm or less, and the area ratio of the crystalline structure may be 5% or less based on the total area of ​​the silicon-based active material.

[0054] In another embodiment, the area ratio of the crystalline texture may be 5% or less, 3% or less, or 0.1% or more, based on the total area of ​​the silicon-based active material.

[0055] That is, the silicon-based active material according to the present application has a crystal grain size of 200 nm or less, and the size of each crystal structure is small, so that the above-mentioned area ratio can be satisfied, and thus the distribution of the grain boundaries can be widened, thereby achieving the above-mentioned effects.

[0056] In one embodiment of the present application, the silicon-based active material may contain 20 or more crystalline structures.

[0057] In another embodiment, the number of crystalline structures contained in the silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may be in the range of 60 or less, or 50 or less.

[0058] 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 crystalline structures that satisfies the above range, the strength of the silicon-based active material itself falls within an appropriate range, and when contained in an electrode, the silicon-based active material can be provided with flexibility and has the characteristic of being able to efficiently suppress volume expansion.

[0059] In this application, the term "crystal grain" refers to a collection of irregularly shaped microscopic crystal particles in a metal or material, and the term "crystal grain size" may refer to the diameter of the observed crystal grain. That is, in this application, the term "crystal grain size" refers to the size of a domain that shares the same crystal orientation within a particle, and is a different concept from the grain size or particle size, which represent the size of a substance.

[0060] In one embodiment of the present application, the crystal grain size can be calculated as a FWHM (Full Width at Half Maximum) value through XRD analysis. The remaining values ​​excluding L are measured through XRD analysis of the silicon-based active material, and the crystal grain size can be calculated based on the Debye-Scherrer equation, which states that FWHM and crystal grain size are inversely proportional to each other. In this case, the Debye-Scherrer equation is as follows:

[0061] [Formula 1-1] FWHM=Kλ / LCosθ

[0062] In the formula 1-1, L is the grain size, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0063] The crystal grains have various shapes and can be measured three-dimensionally. Generally, the size of the crystal grains can be measured by a commonly used circle method or diameter measurement method, but is not limited thereto.

[0064] The diameter measurement method involves drawing 5 to 10 equilibrium lines, each with a length of L mm, on a micrograph of the target particle, counting the number of crystal grains z on the lines, and averaging them. Only those that are fully contained are counted, and those that overlap are excluded. If the number of lines is P and the magnification is V, the average particle diameter can be calculated using the following formula 1-2.

[0065] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(um)

[0066] In addition, the circle method involves drawing a circle of a specified diameter on a micrograph of the target particle, and then calculating the average area of ​​the crystal grains from the number of crystal grains that fit within the circle and the number of crystal grains that cross the boundary line, and can be calculated using the following formula 1-3.

[0067] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(um 2 )

[0068] In the above formulas 1-3, Fm is the average particle area, Fk is the measured area on the photograph, z is the number of particles that fit inside the circle, n is the number of particles that span the arc, and V is the magnification of the microscope.

[0069] In one embodiment of the present application, the silicon-based active material has a surface area of ​​0.25 m 2 / g or more.

[0070] In another embodiment, the silicon-based active material has a surface area of ​​0.25 m 2 / g or more, preferably 0.28m 2 / g or more, more preferably 0.30m 2 / g or more, specifically 0.31m 2 / g or more, more specifically 0.32m 2 The silicon-based active material may have a surface area of ​​3 m / g or more. 2 / g or less, preferably 2.5m 2 / g or less, more preferably 2.2m 2 The surface area can be measured (using nitrogen) according to DIN 66131:

[0071] The silicon-based active material has the above surface area, and the size of the surface area of ​​the silicon-based active material can be adjusted by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material. That is, when the silicon-based active material is manufactured using the manufacturing method of the present application, the rough surface results in a larger surface area than particles having the same particle size. In this case, by satisfying the above range and increasing the binding strength with the binder, it has the characteristic of being able to mitigate cracks in the electrode caused by repeated charge-discharge cycles.

[0072] Furthermore, lithium ions are inserted uniformly during intercalation, reducing the stress applied when lithium ions are inserted into silicon particles, thereby mitigating particle cracking. As a result, the negative electrode has the characteristic of improving its life stability. If the surface area is less than the above range, even if the particle size is the same, the surface will be smooth, reducing the binding strength with the binder and causing electrode cracking. In this case, lithium ions will be inserted non-uniformly within the particles, resulting in greater stress due to ion intercalation and particle cracking.

[0073] In one embodiment of the present application, the silicon-based active material satisfies the range of the following formula 2-1. [Formula 2-1] X1 / Y1≦0.960

[0074] In the formula 2-1, X1 is the actual area of ​​the silicon-based active material, Y1 means the area of ​​a spherical particle having the same circumference as the silicon-based active material.

[0075] The formula 2-1 can be measured using a particle analyzer. Specifically, the silicon-based active material according to the present application is scattered on a glass plate using an air jet, and then a shadow image of the scattered silicon-based active material particles is photographed, and the shapes of 10,000 silicon-based active material particles in the photograph can be measured. In this case, the formula 2-1 is a value representing the average value for 10,000 particles. The formula 2-1 according to the present application can be measured from the image, and the formula 2-1 can be expressed as the sphericity of the silicon-based active material. The sphericity is calculated as [4π * actual area of ​​silicon-based active material / (boundary) 2 ] may also be expressed as

[0076] In one embodiment of the present application, the sphericity of the silicon-based active material may be, for example, 0.960 or less, for example, 0.957 or less. The sphericity of the silicon-based active material may be 0.8 or more, for example, 0.9 or more, specifically 0.93 or more, more specifically 0.94 or more, for example, 0.941 or more.

[0077] In one embodiment of the present application, the silicon-based active material satisfies the range of the following formula 2-2.

[0078] [Formula 2-2] X2 / Y2≦0.995

[0079] In the formula 2-2, Y2 is the actual periphery of the silicon-based active material, X2 is the perimeter of the circumscribing figure of the silicon-based active material.

[0080] The formula 2-2 can be measured using a particle analyzer. Specifically, the silicon-based active material according to the present application is scattered on a glass plate using an air jet, and then a shadow image of the scattered silicon-based active material particles is photographed, and the shapes of 10,000 silicon-based active material particles in the photograph are measured. In this case, the formula 2-2 represents an average value for 10,000 particles. The formula 2-2 according to the present application can be measured from the image, and the formula 2-2 can be expressed as the convexity of the silicon-based active material.

[0081] In one embodiment of the present application, the range of X2 / Y2≦0.996, preferably X2 / Y2≦0.995, may be satisfied, and the range of 0.8≦X2 / Y2, preferably 0.9≦X2 / Y2, more preferably 0.95≦X2 / Y2, specifically 0.98≦X2 / Y2 may be satisfied.

[0082] The smaller the value of the formula 2-1 or 2-2, the greater the roughness of the silicon-based active material. By using a silicon-based active material having such a range, the bonding strength with the binder increases, thereby providing the characteristic of being able to alleviate cracks in the electrode caused by repeated charge-discharge cycles.

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

[0084] The silicon-based active material containing silicon-based particles having a particle size distribution of 0.01 μm to 30 μm means that the silicon-based active material contains a large number of individual silicon-based particles having particle sizes within the range, and the number of silicon-based particles contained is not limited.

[0085] The particle size of the silicon-based particles may be expressed as their diameter if they are spherical. However, even if the particles are not spherical, the particle size may be measured by comparing it with the spherical shape. The particle size of individual silicon-based particles may be measured by a method generally used in the art.

[0086] On the other hand, 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. If the average particle size is less than 5 μm, the specific surface area of ​​the particles increases excessively, resulting in an excessive increase in the viscosity of the negative electrode slurry. As a result, the particles constituting the negative electrode slurry are not dispersed smoothly. Furthermore, if the size of the silicon-based active material is too small, the contact area between the silicon particles and the conductive material decreases due to the formation of a composite of the conductive material and the binder in the negative electrode slurry, increasing the possibility of the conductive network being broken and resulting in a decrease in capacity retention. On the other hand, if the average particle size exceeds 10 μm, the presence of excessively large silicon particles results in an insufficient smooth surface for the negative electrode, resulting in uneven current density during charge and discharge. Furthermore, if the silicon particles are too large, the phase stability of the negative electrode slurry becomes unstable, resulting in poor processability. This results in a decrease in the capacity retention of the battery.

[0087] 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 electrode active material is preferably 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET surface area is determined according to DIN 66131 (using nitrogen).

[0088] In one embodiment of the present application, the silicon-based active material can be, for example, in crystalline or amorphous form, and is preferably not porous.The silicon particles are preferably spherical or shard-like particles.Alternatively, but less preferably, the silicon particles may have a fibrous structure or be in the form of a silicon-containing film or coating.

[0089] In one embodiment of the present application, the negative electrode composition is provided, in which the silicon-based active material is 70 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0090] In another embodiment, the silicon-based active material may be included in an amount of 70 parts by weight or more, preferably 75 parts by weight or more, more preferably 80 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0091] The negative electrode active material layer composition according to the present application solves the problems of surface deterioration during charge and discharge, uniformity during pre-lithiation, and gas generation without reducing the capacity performance of the entire negative electrode, even when a silicon-based active material with extremely high capacity is used within the above range, by combining it with a ceramic layer (described later). Furthermore, by using a specific negative electrode conductive material and negative electrode binder that can suppress the volume expansion rate during charge and discharge, the negative electrode performance is not reduced even when the above range is included, and the composition has excellent output characteristics during charge and discharge.

[0092] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the sphericity thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0093] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter. [Formula 1] 4πA / P 2

[0094] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into them to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, even if the properties of silicon-based active materials themselves are adjusted as described above, the volume of silicon-based active materials can rapidly expand during charge / discharge processes, potentially damaging the conductive paths formed within the negative electrode active material layer.

[0095] Therefore, in one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the negative electrode active material layer composition includes at least one selected from the group consisting of a negative electrode conductive material; and a negative electrode binder.

[0096] 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-like conductive material, a sheet-like conductive material, and a linear conductive material.

[0097] 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 conductivity to the negative electrode and has conductivity without inducing a chemical change. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which realizes high conductivity and excellent dispersibility.

[0098] 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 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0099] In one embodiment of the present application, the dot-like conductive material may have a functional group content (volatile matter) of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0100] In particular, when the functional group content of the dot-like conductive material satisfies the above range, functional groups are present on the surface of the dot-like conductive material, and when water is used as a solvent, the dot-like conductive material can be smoothly dispersed in the solvent.

[0101] 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 depending on the degree of heat treatment of the dot-like conductive material.

[0102] That is, in the production of the point-like conductive material, a high content of functional groups means that there is a lot of foreign matter, and a low content of functional groups means that more heat treatment processing has been performed.

[0103] 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.

[0104] In one embodiment of the present application, the negative electrode conductive material may include a sheet conductive material.

[0105] 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.

[0106] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may be preferably platelet graphite.

[0107] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size satisfies this range, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersing using the same device and time, the dispersion effect is excellent.

[0108] In one embodiment of the present application, the sheet conductive material may have 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.

[0109] 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.

[0110] In one embodiment of the present application, the sheet conductive material can be a high-specific surface area sheet conductive material or a low-specific surface area sheet conductive material without any restrictions. However, the sheet conductive material of the present application in particular may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low-specific surface area sheet conductive material that does not cause dispersion problems.

[0111] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0112] In another embodiment, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m2 / g or more 250m 2 / g or less.

[0113] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0114] In another embodiment, the sheet conductive material is a sheet conductive material with a low specific surface area, and has a BET specific surface area of ​​5 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0115] 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 side by side or entangled with their longitudinal axes aligned in substantially the same direction, forming a bundle or rope-like shape. The carbon nanotube units have cylindrical graphite sheets with nanosized diameters and an sp2 bonding structure. Depending on the winding angle and structure of the graphite sheets, the units may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode, and improving the conductivity of the negative electrode.

[0116] In one embodiment of the present application, the linear conductive material may include SWCNT; or MWCNT.

[0117] In one embodiment of the present application, there is provided a negative electrode composition in which the negative electrode conductive material is contained in an amount of 10 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0118] In another embodiment, the negative electrode conductive material may be included in an amount of 10 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 10 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0119] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the negative electrode conductive material comprises a sheet conductive material and a linear conductive material, and the sheet conductive material is contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0120] In another embodiment, the amount of the planar conductive material may be 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, and more preferably 95 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0121] In another embodiment, the amount of the linear conductive material may be 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.1 parts by weight or more and 10 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0122] In particular, in one embodiment of the present application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each of which satisfies the above-mentioned composition and ratio, thereby not significantly affecting the life characteristics of existing lithium secondary batteries, increasing the number of points at which charging and discharging are possible, and providing the characteristic of excellent output characteristics at high C-rates.

[0123] 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 secure the contact points between the silicon-based active materials, which undergo a very large volume expansion of the electrodes upon charge and discharge, while the positive electrode conductive material serves to provide partial conductivity while acting as a buffer having a shock-absorbing function during rolling, and therefore has a completely different structure and role from the negative electrode conductive material of the present invention.

[0124] 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.

[0125] 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 generally used as a conventional negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dotted shape to facilitate the storage and release of lithium ions.

[0126] Meanwhile, 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. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but rather a material for ensuring a planar conductive path within the negative electrode active material layer.

[0127] 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 to ensure a conductive path rather than to store or release 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.

[0128] 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 plays a role in storing or releasing lithium.

[0129] 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 4.5m 2 The plate-shaped graphite, which is a planar conductive material, may have a planar BET specific surface area of ​​5 m 2 / g or more.

[0130] 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.

[0131] The negative electrode binder according to one embodiment of the present application plays a role in holding down the active material and conductive material to prevent twisting and structural deformation of the negative electrode structure when the volume expansion and relaxation of the silicon-based active material occurs. Any common binder can be used as long as it fulfills this role. Specifically, a water-based binder can be used, and more specifically, a PAM-based binder can be used.

[0132] In one embodiment of the present application, the amount of the negative electrode binder is 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0133] In particular, the negative electrode binder according to the present application uses a water-based binder due to the high rigidity of the silicon-based active material. The water-based binder is a polymer that exhibits very high rigidity after drying. When a water-based ceramic layer is coated on top of a water-based silicon-based negative electrode active material layer and then dried, the surface becomes intermixed with the water, regardless of how quickly it dries. To address this issue, the ceramic layer according to the present application uses an organic binder and organic solvent, allowing for easy dispersion of the ceramic and organic binder without affecting the water-based negative electrode, resulting in a highly dense coating on the negative electrode active material layer.

[0134] In one embodiment of the present application, the negative electrode active material layer further includes a ceramic layer provided on the surface of the silicon-based negative electrode active material layer opposite to the surface facing the negative electrode current collector layer.

[0135] As described above, the negative electrode for a lithium secondary battery according to the present application includes a ceramic layer, and by incorporating the above-described negative electrode active material, it maintains high capacity and high density characteristics, while resolving the problems of surface deterioration during charge and discharge, the problem of poor uniformity during prelithiation, and the problem of lifespan characteristics due to gas generation.

[0136] Specifically, the primary reason for gas generation in Si-based anodes is the destruction and re-creation of the SEI layer due to the large volume expansion / contraction of the Si active material. In other words, the SEI layer is continuously destroyed and re-created. When the Si particles are broken down due to deep use, new Si surfaces are formed, creating additional reactions that create new SEI layers. This generates gas, which acts as resistance between the electrodes and leads to performance degradation. To solve this problem, a ceramic layer, described below, is used on top of the anode active material layer.

[0137] In one embodiment of the present application, the ceramic layer may comprise a ceramic layer composition or a dried product thereof.

[0138] In this case, "including the ceramic layer composition" may mean that the ceramic layer contains the ceramic layer composition as is, and "including the dried product of the ceramic layer composition" may mean that all of the organic solvent that may be contained in the ceramic layer composition has been dried and removed, and is not contained in the ceramic layer.

[0139] In one embodiment of the present application, the ceramic layer may have a thickness of 0.5 μm or more and 10 μm or less.

[0140] In another embodiment, the thickness of the ceramic layer may be 0.5 μm or more and 8 μm or less, preferably 2 μm or more and 6 μm or less.

[0141] As described above, when the thickness of the ceramic layer satisfies the above range, the effect of improving stability by controlling the prelithiation rate during prelithiation can be obtained. If the thickness of the ceramic layer exceeds the above range, problems such as deterioration of negative electrode performance may occur, and even efficiency during prelithiation may be reduced. Furthermore, if the thickness of the ceramic layer is less than the above range, it may be difficult to control the prelithiation rate, and problems such as electrode deterioration due to surface reactions on the upper part of the negative electrode active material layer may occur, resulting in a shortened lifespan.

[0142] Furthermore, it was confirmed that by satisfying the above range, the gas adsorption characteristics are particularly excellent.

[0143] In one embodiment of the present application, the ceramic layer composition may include a ceramic and a binder, and the ceramic may include 10 parts by weight or more and 50 parts by weight or less of BaTiO3 based on 100 parts by weight of the ceramic.

[0144] More specifically, the ceramic may contain 10 parts by weight or more and 50 parts by weight or less, preferably 15 parts by weight or more and 40 parts by weight or less, and more preferably 20 parts by weight or more and 35 parts by weight or less of BaTiO3, based on 100 parts by weight of the ceramic.

[0145] In one embodiment of the present application, the ceramic can be used without limitation as long as it can function as the ceramic layer. Specifically, Al2O3, ZrO2, SiO 2、 Provided is a negative electrode for a lithium secondary battery, which contains one or more materials selected from the group consisting of TiO2, ZnO, BaTiO3, SrTiO3, CaCO3, CaO, CeO2, NiO, MgO, SnO2, Y2O3, Pb(Zr,Ti)O3 (PZT), (Pb,La)(Zr,Ti)O3 (PLZT), PB(Mg3Nb2 / 3)O3-PbTiO3 (PMN-PT), and hafnia (HfO2).

[0146] As described above, various ceramics can be used without limitation, but among them, BaTiO3 is contained in the above weight parts. By containing the above weight parts of ceramic, BaTiO3 has a structure that is most effective for containing gas generated at the anode, and has excellent gas adsorption properties. In addition, by further containing other ceramics, it can function as a buffer layer.

[0147] In one embodiment of the present application, the ceramic contains BaTiO3 and Al2O3, and the BaTiO3 content is 10 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the ceramic.

[0148] Specifically, the ceramic may contain BaTiO3 and Al2O3 and satisfy a weight ratio of BaTiO3:Al2O3=80:20.

[0149] In one embodiment of the present application, the ceramic layer composition may further include a solvent, which may be completely removed when the ceramic layer is formed.

[0150] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the solvent includes at least one selected from the group consisting of N-methylpyrrolidone (NMP); dimethylformamide (DMF); acetone; and dimethylacetamide.

[0151] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the binder is polyvinylidene fluoride (PVdF); or polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP).

[0152] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, in which the surface of the ceramic layer opposite to the surface facing the negative electrode active material layer is joined to lithium metal, and the adhesive strength after leaving the surface at 23°C for 10 seconds to 2 minutes is 10 gf / 15 mm or more and 100 gf / 15 mm or less.

[0153] The adhesive strength was measured using a peel strength tester at a 90° angle and a speed of 5 mm / s using 3M 9070 tape. Specifically, one side of the lithium metal layer of a negative electrode, in which a lithium metal layer was laminated on top of a ceramic layer, was attached to one side of a slide glass (3M 9070 tape) to which an adhesive film had been attached. Then, a 2 kg rubber roller was used to roll the adhesive 5 to 10 times, and the adhesive strength (peel strength) was measured at a 90° angle and a speed of 5 mm / s. The adhesive strength was measured at 23°C and atmospheric pressure.

[0154] In one embodiment of the present application, normal pressure may refer to pressure in a state where no specific pressure is applied or reduced, and may be used in the same sense as atmospheric pressure. Generally, normal pressure may be expressed as 1 atmosphere.

[0155] In one embodiment of the present application, the surface of the ceramic layer opposite to the surface facing the negative electrode active material layer may be joined to lithium metal, and then the adhesive strength after being left at 23°C for 10 seconds to 2 minutes may be 10 gf / 15 mm or more and 100 gf / 15 mm or less, preferably 15 gf / 15 mm or more and 95 gf / 15 mm or less, and more preferably 20 gf / 15 mm or more and 50 gf / 15 mm or less.

[0156] As described above, when the adhesive strength between the ceramic layer and lithium metal satisfies the above range, when the lithium metal is transferred using the transfer process in the pre-lithiation process, in particular, the adhesive strength between the lithium metal and the ceramic layer is good and transferability is ensured, and problems such as reverse transfer do not occur, allowing the pre-lithiation process to proceed smoothly.

[0157] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, comprising, based on 100 parts by weight of the ceramic layer composition, 60 parts by weight or more and 95 parts by weight or less of the ceramic, and 5 parts by weight or more and 40 parts by weight or less of the binder.

[0158] In this case, the organic solvent contained in the ceramic layer composition does not correspond to an effective material, and the reference of 100 parts by weight of the ceramic layer composition may refer to the parts by weight including only the ceramic and binder.

[0159] In one embodiment of the present application, the ceramic may be present in an amount of 60 parts by weight or more and 95 parts by weight or less, preferably 65 parts by weight or more and 90 parts by weight or less, and more preferably 70 parts by weight or more and 90 parts by weight or less, based on 100 parts by weight of the ceramic layer composition.

[0160] In one embodiment of the present application, the binder may be present in an amount of 5 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 35 parts by weight or less, and more preferably 10 parts by weight or more and 30 parts by weight or less, based on 100 parts by weight of the ceramic layer composition.

[0161] As described above, since the ceramic layer composition contains the binder and ceramic in the containing portion, the dispersibility of the binder and ceramic is improved and they are uniformly formed in the ceramic layer, which allows for smooth control of the prelithiation rate and satisfies an appropriate viscosity range, thereby improving the coating density when coating the ceramic layer.

[0162] In one embodiment of the present application, the negative electrode active material layer may have a thickness of 10 μm to 200 μm.

[0163] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be a pre-lithiated negative electrode.

[0164] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including the steps of: preparing a negative electrode current collector layer; applying a negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a negative electrode active material layer; and applying a ceramic layer composition to a surface of the negative electrode active material layer opposite to the surface facing the negative electrode current collector layer to form a ceramic layer, wherein the ceramic layer has a thickness of 0.5 μm to 10 μm, the ceramic layer composition includes a ceramic and a binder, and contains 10 parts by weight to 50 parts by weight of BaTiO3 per 100 parts by weight of the ceramic.

[0165] In the method for manufacturing the negative electrode, the composition and content included in each step may be the same as those described above.

[0166] In one embodiment of the present application, a step of forming a negative electrode active material layer by coating a negative electrode active material layer composition on one or both surfaces of the negative electrode current collector layer is provided.

[0167] That is, the step of forming a negative electrode active material layer on a negative electrode current collector layer may refer to a step of forming an active material layer on a surface opposite to the current collector layer.

[0168] In one embodiment of the present application, applying the negative electrode active material layer composition includes applying and drying a negative electrode slurry containing the negative electrode active material layer composition and a negative electrode slurry solvent.

[0169] In this case, the solid content of the negative electrode slurry may be in the range of 10% to 40%.

[0170] In one embodiment of the present application, the step of forming the negative electrode active material layer may include mixing the negative electrode slurry; and coating one or both surfaces of the negative electrode current collector layer with the mixed negative electrode slurry, and the coating may be performed using a coating method commonly used in the art.

[0171] Thereafter, in one embodiment of the present application, a ceramic layer composition is applied to a surface of the negative electrode active material layer opposite to the surface facing the negative electrode current collector layer to form a ceramic layer.

[0172] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including the steps of applying the ceramic layer composition, drying and rolling the applied ceramic layer composition to remove an organic solvent from the ceramic layer composition.

[0173] In one embodiment of the present application, the negative electrode slurry solvent may be used without limitation as long as it can dissolve and disperse the negative electrode active material layer composition, and specifically, water or NMP may be used.

[0174] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including a step of pre-lithiating a negative electrode in which a negative electrode active material layer and a ceramic layer are formed on the negative electrode current collector, the step of pre-lithiating the negative electrode including a lithium electroplating process; a lithium metal transfer process; a lithium metal vapor deposition process; or a stabilized lithium metal powder (SLMP) coating process.

[0175] The negative electrode for a lithium secondary battery described above includes SiOx (x=0) as a negative electrode active material layer to enhance capacity characteristics, and the ceramic layer is provided with the specific composition and thickness described above, thereby providing the advantages of fast charging. That is, compared to a case where only a negative electrode active material layer is provided, the ceramic layer has the above composition, enabling a uniform pre-lithiation process at the upper end of the negative electrode, thereby further improving the battery life.

[0176] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0177] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0178] The porosity varies depending on the composition and content of the silicon-based active material, the negative electrode conductive material, and the negative electrode binder contained in the negative electrode active material layer, and is characterized by the fact that the electrode has an appropriate range of electrical conductivity and resistance.

[0179] 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.

[0180] A secondary battery according to an embodiment of the present specification may include the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode may be the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0181] 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.

[0182] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0183] The positive electrode active material may be a commonly used positive electrode active material, such as a layered compound or a compound substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); 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 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.6 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides 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≦0.6) 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 substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0184] In one embodiment of the present application, the positive electrode active material includes a lithium transition metal composite compound including nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium transition metal composite compound may include single particles or secondary particles, and the single particles may have an average particle size (D50) of 1 μm or more.

[0185] For example, the average particle size (D50) of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 12 μm or less, more than 1 μm and 8 μm or less, or more than 1 μm and 6 μm or less.

[0186] The single particles can have excellent particle strength even when they are formed with a small particle size (D50) of 1 μm or more and 12 μm or less. For example, the single particles can have a strength of 650 kgf / cm 2 When the particle is rolled with a force of 650 kgf / cm, the particle strength is 100 MPa to 300 MPa. 2 Even if the electrode is rolled with a strong force, the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, thereby improving the life characteristics of the battery.

[0187] The single particles may be prepared by mixing a transition metal precursor and a lithium source material and calcining the mixture. The secondary particles may be prepared by a method different from that of the single particles, and the composition thereof may be the same as or different from that of the single particles.

[0188] The method for forming the single particles is not particularly limited, but they can generally be formed by over-firing at an elevated firing temperature, and can be prepared by using additives such as grain growth promoters that are useful for over-firing, or by changing the starting material.

[0189] For example, the calcination is performed at a temperature that allows the formation of single particles. To achieve this, the calcination must be performed at a temperature higher than that used for the production of secondary particles. For example, when the precursor composition is the same, the calcination temperature should be about 30°C to 100°C higher than that used for the production of secondary particles. The calcination temperature for the formation of the single particles may vary depending on the metal composition of the precursor. For example, when a high-nickel (Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more is formed as single particles, the calcination temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the calcination temperature satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. When the calcination temperature is lower than 790°C, a positive electrode active material containing a lithium composite transition metal compound in the form of secondary particles can be produced. However, when the calcination temperature exceeds 950°C, excessive calcination occurs, preventing the formation of a layered crystal structure and resulting in poor electrochemical properties.

[0190] In this specification, the term "single particle" is used to distinguish it from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and a pseudo-single particle form that is an agglomeration of 30 or less primary particles.

[0191] Specifically, the single particle in the present invention may be in the form of a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0192] In one embodiment of the present application, the lithium transition metal composite compound serving as the positive electrode active material further includes secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0193] In the present invention, the single particle may be in the form of a single particle consisting of one primary particle or a pseudo-single particle which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0194] The lithium transition metal composite compound may further include secondary particles. The secondary particles refer to a form formed by aggregation of primary particles, and can be distinguished from the concept of single particles, which includes one primary particle, one single particle, or a pseudo-single particle form that is an aggregation of 30 or less primary particles.

[0195] The particle diameter (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g~10m 2 / g, preferably 0.1m 2 / g~1m 2 / g, and more preferably 0.3m 2 / g~0.8m 2 / g.

[0196] In a further embodiment of the present application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0197] When the average particle size (D50) of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially reducing output characteristics.

[0198] According to a further embodiment of the present invention, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, so that the single particles can have excellent particle strength even when formed with a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, thereby improving the life characteristics of the battery.

[0199] In one embodiment of the present application, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles by 1 μm to 18 μm.

[0200] For example, the average particle size (D50) of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0201] When the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, for example, when the above range is satisfied, the single particles can have excellent particle strength even though they are formed with a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, and thereby improving the life characteristics and energy density of the battery.

[0202] According to a further embodiment of the present application, the single particles are contained in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material, or may be contained in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0203] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, relative to 100 parts by weight of the positive electrode active material. The single particles may be included in an amount of 100 parts by weight or less, relative to 100 parts by weight of the positive electrode active material.

[0204] When the single particles are contained in the above range, excellent battery characteristics can be exhibited in combination with the above-mentioned negative electrode material. In particular, when the single particles are contained in an amount of 15 parts by weight or more, the increase in fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery life characteristics.

[0205] In one embodiment of the present application, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 0 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0206] When the above range is satisfied, the above-described effects due to the presence of the single particle positive electrode active material can be maximized. When the secondary particle positive electrode active material is included, the components thereof may be the same as or different from those exemplified for the single particle positive electrode active material, and may refer to an aggregated form of single particles.

[0207] In one embodiment of the present application, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, in 100 parts by weight of the positive electrode active material layer.

[0208] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0209] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without undergoing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and the like, and one or more of these may be used alone or in combination.

[0210] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0211] The separator separates the negative electrode and 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 that exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification capacity is preferred. Specifically, a porous polymer film, such as a porous polymer film made from 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 from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may also be used, and may be used in a single-layer or multi-layer structure.

[0212] In particular, by having a ceramic layer on the silicon-based negative electrode active material layer according to the present application, the ceramic layer formed on the separator can be eliminated or minimized, the thickness of the separator roll can be reduced, and the separator can have excellent process and cost characteristics.

[0213] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0214] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0215] Examples of the non-aqueous organic solvent that may 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.

[0216] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte with high electrical conductivity can be produced, and therefore, these cyclic carbonates are more preferably used.

[0217] 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:

[0218] In addition to the electrolyte components, 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 purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0219] 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 the battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and 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. [Example]

[0220] Below, preferred examples are presented to help understand the present invention, but these examples are for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical ideas of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0221] <Example> <Production of negative electrodes> Example 1: Preparation of negative electrode Production of negative electrode active material layer A negative electrode active material layer composition was prepared by mixing Si (average particle size (D50): 5 μm) as a silicon-based active material, first conductive material, second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10. The negative electrode active material layer composition was added to distilled water as a solvent for forming a negative electrode slurry (solid concentration: 28 wt%).

[0222] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material is carbon nanotubes.

[0223] The mixing method was as follows: the first conductive material, the second conductive material, the binder, and the water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added, followed by dispersion at 2500 rpm for 30 minutes to prepare a slurry.

[0224] The negative electrode slurry was applied at 3.00 mg / cm to both sides of a copper current collector (thickness: 15 μm) as a negative electrode current collector. 2 The coated layer was rolled and then dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer (thickness: 23 μm).

[0225] Ceramic layer production The ceramic layer composition was prepared by mixing BaTiO3:Al2O3 as the ceramic in a ratio of 20:80 based on 100 parts by weight of the ceramic, and adding 20 parts by weight of PVdF as the binder based on 100 parts by weight of the ceramic layer composition.Then, the ceramic layer composition was prepared by adding it to acetone as the solvent (solid concentration 18% by weight).

[0226] Then, the ceramic layer composition was coated on the negative electrode active material layer, roll pressed, and dried in a vacuum oven at 60° C. for 10 hours to form a ceramic layer (thickness: 4 μm).

[0227] A negative electrode was manufactured in the same manner as in Example 1, except that the conditions for manufacturing the negative electrode active material layer and the ceramic layer were changed as follows.

[0228] [Table 1]

[0229] <Secondary battery manufacturing> LiNi as the positive electrode active material 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%).

[0230] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) 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), and a positive electrode was fabricated (positive electrode thickness: 77 μm, porosity: 26%).

[0231] An electrolyte was injected between the positive electrode and the negative electrode of Example 1 via a polyethylene separator, to prepare the secondary battery of Example 1.

[0232] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 30:70, to which vinylene carbonate was added at 3 wt% based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0233] Secondary batteries were fabricated in the same manner as above, except that the negative electrodes of Examples 2 to 4 and Comparative Examples 1 to 6 were used.

[0234] Experimental example 1: Evaluation of Monocell life The secondary batteries fabricated above were subjected to a lifespan evaluation using an electrochemical charge / discharge machine to evaluate their capacity retention. This evaluation was conducted at a high temperature in order to evaluate the gas generation experiment in Experimental Example 2, which will be described later. The secondary batteries were subjected to 100 cycles of charging (1.0 C CC / CV charging, 4.2 V, 0.05 C cut) and discharging (0.5 C CC discharge, 3.0 V cut) at 45°C, and then the capacity retention was measured.

[0235] The capacity retention rate at the 100th time was evaluated using the following formula, and the results are shown in Table 2 below.

[0236] Capacity retention rate (%) = {(discharge capacity at 100th cycle) / (discharge capacity at 1st cycle)} × 100

[0237] [Table 2]

[0238] Lifespan evaluations are generally conducted at room temperature (25°C), but because significant gas generation due to side reactions occurs only after a long lifespan, the evaluation was conducted at a higher temperature where more gas is generated. At higher temperatures, significant differences were observed because more reactions that form the SEI layer occur along with gas generation due to side reactions, making it easier to assess the impact on ceramic particles.

[0239] The results of the lifespan evaluation in Table 2 confirmed that the Examples performed better than the Comparative Examples. Among the Examples, Example 1, which had an optimal ratio of small-particle BaTiO3 and relatively large-particle Al2O3, showed the best performance, and Example 4 confirmed that when the same ceramic composition is used and the thickness is reduced, the resistance due to the thickness of the separator ceramic layer decreases, resulting in some performance improvements.

[0240] In addition, Examples 5 to 8 each have a higher silicon content, and the proportion of BaTiO3 is also increased accordingly. That is, in the case of Examples 5 to 8, as the content of the silicon-based active material increases, the conductive material and binder decrease, and it can be confirmed that there is a partial decrease in performance compared to Examples 1 to 4, but it can be confirmed that the capacity retention rate is very good compared to the comparative example.

[0241] Comparative Example 1 has a high proportion of BaTiO3, which may be effective for gas removal, but because the particles are small, the packing density of the ceramic layer is increased, preventing ion migration and reducing ion conductivity, resulting in reduced lifespan.

[0242] In Comparative Example 2, the proportion of BaTiO3 was relatively low, and the resistance of the separator was low, but gas generation could not be effectively suppressed, and local gas traps were generated between the electrode and the separator, which is thought to have reduced the lifespan.

[0243] Comparative Example 3 was a single composition of BaTiO3, and was evaluated as having a high battery resistance due to the same effect as Comparative Example 1. Comparative Example 4, like Comparative Example 2, also had no major problems with resistance, but was unable to suppress gas generation.

[0244] Comparative Examples 5 and 6 have the same composition as Comparative Example 1, but are thicker or thinner. When the thickness is thick, as in Comparative Example 5, the performance deteriorates due to increased resistance, and when the thickness is very thin, as in Comparative Example 6, the absolute amount of BaTiO3 is very small, which is considered to have shown a similar trend to Comparative Example 2, where the BaTiO3 content is very low.

[0245] Experimental Example 2: Gas analysis results (after 100 cycles of mono cell life) After the mono cell evaluated earlier had reached 100 cycles of life, an analysis was carried out to check the gas generation status. Qualitative analysis was carried out using GC / MS equipment, and the 11 gases (H2, CO, CO) that were most frequently generated by reaction with the electrolyte were analyzed. 2、 CH4, C2H 2、 The results are shown in Table 3 below.

[0246] [Table 3]

[0247] Gas analysis confirmed that examples with appropriate BaTiO3 content and thickness generated less gas. Also, it was confirmed that Example 2, which had a high BaTiO3 content, and Example 3, which had a large ceramic layer thickness and a small composition but a large quantitative amount of BaTiO3, generated less gas than Example 1. Example 4, which was relatively thin and had a BaTiO3 composition of 20, generated more gas than Examples 1 to 3.

[0248] The Comparative Examples generally show higher gas generation rates than the Examples, but this is due to the influence of the quantitative amount of BaTiO3. Comparative Examples 1, 3, and 5 correspond to cases where the BaTiO3 content is high, the BaTiO3 is a single composition, or the thickness is large and the absolute amount is high, and in these cases, the total gas generation rate is similar to that of the Examples.

[0249] However, in the case of Comparative Examples 2, 4, and 6, when the Al2O3 content was high or alone, or when the thickness was thin and the amount of BaTiO3 was small, the amount of gas generation was found to be large, and it was determined that this affected the life performance.

[0250] That is, as can be seen from Tables 2 and 3, the battery using the negative electrode according to the present application has an excellent lifespan maintenance rate and is characterized by improved performance due to suppression of gas generation. [Explanation of symbols]

[0251] 10. Ceramic layer 20...Negative electrode active material layer 30 Negative electrode current collector layer

Claims

1. 1. A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a silicon-based negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a ceramic layer provided on a surface of the silicon-based negative electrode active material layer opposite to the surface facing the negative electrode current collector layer, the ceramic layer comprises a ceramic layer composition or a dried product thereof; The thickness of the ceramic layer is 0.5 μm or more and 10 μm or less, the ceramic layer composition comprises a ceramic and a binder; Based on 100 parts by weight of the ceramic, BaTiO ３ A negative electrode for a lithium secondary battery comprising 10 parts by weight or more and 50 parts by weight or less.

2. The ceramic is Al ２ O ３ , ZrO ２ , SiO ２ , TiO ２ , ZnO, BaTiO ３ , SrTiO ３ , CaCO ３ , CaO, CeO ２ , NiO, MgO, SnO ２ , Y ２ O ３ , Pb(Zr,Ti)O ３ (PZT), (Pb, La) (Zr, Ti) O ３ (PLZT), Pb(Mg 1／３ Nb ２／３ ) O ３ -PbTiO ３ (PMN-PT) and hafnia (HfO ２ 2. The negative electrode for a lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of:

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the binder is polyvinylidene fluoride (PVdF); or polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP).

4. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the ceramic is present in an amount of 60 to 95 parts by weight, and the binder is present in an amount of 5 to 40 parts by weight, based on 100 parts by weight of the ceramic layer composition.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein a surface of the ceramic layer opposite to the surface facing the silicon-based negative electrode active material layer is joined to metallic lithium, and the surface is allowed to stand at 23°C for 10 seconds to 2 minutes, after which the adhesive strength is 10 gf / 15 mm or more and 100 gf / 15 mm or less.

6. the silicon-based negative electrode active material layer contains a negative electrode active material layer composition, 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer composition comprises at least one selected from the group consisting of a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

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

8. The negative electrode conductive material includes a sheet conductive material and a linear conductive material, 7. The negative electrode for a lithium secondary battery according to claim 6, wherein the sheet conductive material is contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

9. The negative electrode for a lithium secondary battery according to claim 6 , wherein the silicon-based active material is contained in an amount of 70 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

10. providing a negative electrode current collector layer; forming a negative electrode active material layer by applying a negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer; and forming a ceramic layer by applying a ceramic layer composition to a surface of the negative electrode active material layer opposite to the surface facing the negative electrode current collector layer; A method for producing a negative electrode for a lithium secondary battery, comprising: The thickness of the ceramic layer is 0.5 μm or more and 10 μm or less, the ceramic layer composition comprises a ceramic and a binder; Based on 100 parts by weight of the ceramic, BaTiO ３ The negative electrode for a lithium secondary battery comprises 10 parts by weight or more and 50 parts by weight or less.

11. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 10, further comprising the step of drying and rolling the ceramic layer composition to remove a solvent from the ceramic layer composition after the ceramic layer composition is applied.

12. pre-lithiating the negative electrode, in which the negative electrode active material layer and the ceramic layer are formed on the negative electrode current collector layer; 11. The method of claim 10, wherein the prelithiation of the negative electrode comprises a lithium electroplating process; a lithium metal transfer process; a lithium metal vapor deposition process; or a stabilized lithium metal powder (SLMP) coating process.

13. positive electrode; The negative electrode for a lithium secondary battery according to any one of claims 1 to 9; a separator disposed between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising:

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