Negative electrode for lithium secondary battery, method for manufacturing negative electrode for lithium secondary battery, and lithium secondary battery including negative electrode

Abstract

To provide a negative electrode for a lithium secondary battery, a manufacturing method of the negative electrode for the lithium secondary battery, and the lithium secondary battery including the negative electrode.SOLUTION: The present application relates to a negative electrode for a lithium secondary battery, a method for manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including a negative electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0180143, filed with the Korean Intellectual Property Office on December 15, 2021, 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 released 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 of increasing capacity by using silicon-based compounds such as Si / C and SiOx, which have capacities more than 10 times larger than graphite-based materials, as negative electrode active materials. However, while silicon-based compounds, which are high-capacity materials, have a higher capacity than the conventionally used graphite, they suffer from the problem of rapidly expanding in volume during charging, which breaks the conductive path and reduces battery performance.

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

[0009] Furthermore, when making a negative electrode using a silicon-based active material, it is important that the pore structure of the negative electrode is simple, and it is known that it is advantageous to increase the particle size of the silicon-based active material contained therein. However, due to the characteristics of silicon-based active materials, swelling during charge / discharge is large. This is because the larger the particle size, the greater the volume change. Furthermore, as the particle size increases, the surface area in contact with the negative electrode current collector layer decreases, which can lead to electrode detachment.

[0010] Therefore, even when silicon-based compounds are used as active materials to improve capacity performance, research is needed into silicon-based active material layers that can simplify the pore structure of the negative electrode and prevent damage to the conductive path due to the volume expansion of the silicon-based compounds. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent Publication No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0012] As mentioned above, silicon-based active materials have excellent capacity characteristics, and their application to negative electrodes has been discussed, but their use is limited by the complex pore structure of the negative electrode due to the size of the active material itself and issues such as volume expansion during charge and discharge. However, even when silicon-based active materials are used in negative electrodes, it has been confirmed that by adjusting the median particle size (D50) of the silicon-based active material and arranging it in a specific region, it is possible to simplify the pore structure of the negative electrode and prevent electrode detachment during charge and discharge.

[0013] Therefore, an object of the present application is to provide a negative electrode for a lithium secondary battery having the above-mentioned characteristics, a method for producing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0014] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode composition including a silicon-based active material layer, a negative electrode conductive material, and a negative electrode binder, the silicon-based active material layer comprising silicon-based particles having a particle size distribution of 0.01 μm to 30 μm, the negative electrode active material layer comprising a lower layer portion including a surface facing the negative electrode current collector layer and an upper layer portion including a surface opposite to the surface facing the negative electrode current collector layer, wherein the silicon-based active material contained in the lower layer portion has an average particle size (D50) of 1 μm to 6 μm, the silicon-based active material contained in the upper layer portion has an average particle size (D50) of 7 μm to 15 μm, and the average particle size (D50) of the silicon-based active material contained in the lower layer portion is smaller than the average particle size (D50) of the silicon-based active material contained in the upper layer portion.

[0015] In still another embodiment, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including: preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer to form a second negative electrode active material layer, wherein the first negative electrode active material layer composition and the second negative electrode active material layer composition comprise negative electrode compositions including a silicon-based active material, a negative electrode conductor, and a negative electrode binder, the silicon-based active material comprising silicon-based particles having a particle size distribution in the range of 0.01 μm to 30 μm, the silicon-based active material contained in the first negative electrode active material layer composition having an average particle size (D50) of 1 μm to 6 μm, and the silicon-based active material contained in the second negative electrode active material layer composition having an average particle size (D50) of 7 μm to 15 μm.

[0016] Finally, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0017] In one embodiment of the present invention, a lithium secondary battery negative electrode uses a high-capacity silicon-based active material to produce a high-capacity battery. The silicon-based active material is arranged with its average particle size (D50) adjusted. The negative electrode active material layer includes a lower layer portion including a surface facing the negative electrode current collector layer and an upper layer portion including a surface opposite the surface facing the negative electrode current collector layer. The silicon-based active material in the lower layer portion has an average particle size (D50) smaller than that of the silicon-based active material in the upper layer portion. In particular, the silicon-based active material in the lower layer portion has an average particle size (D50) of 1 μm to 6 μm, and the silicon-based active material in the upper layer portion has an average particle size (D50) of 7 μm to 15 μm.

[0018] As a result, silicon-based active material with a relatively small average particle size is distributed near the negative electrode current collector, which reduces the volume expansion of the active material during charging and discharging, preventing electrode detachment. Silicon-based active material with a relatively large average particle size is placed in the upper layer, simplifying the electrode pore structure and thereby reducing the negative electrode resistance.

[0019] That is, the present invention adjusts the arrangement of the silicon-based active material in the negative electrode active material layer according to the average particle size of the silicon-based active material, and by having the above-mentioned characteristics, it is possible to maintain the high capacity characteristics that are the advantages of a negative electrode containing a silicon-based active material, and also to prevent the electrode from detaching, to prevent an increase in resistance, and to improve the life characteristics. [Brief explanation of the drawings]

[0020] [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. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0021] Prior to describing the present invention, some terms will first be defined. In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0022] In this specification, "p to q" means a range of "not less than p and not more than q." In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mino 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.

[0023] In this specification, "Dn" refers to the particle size distribution, i.e., 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, median particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, particle size distribution may also be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). 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.

[0024] 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.

[0025] It is understood that the term "polymer" is used in the broad sense herein to include copolymers unless "homopolymer" is specifically stated.

[0026] 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.

[0027] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0028] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode composition including a silicon-based active material layer, a negative electrode conductive material, and a negative electrode binder, the silicon-based active material layer comprising silicon-based particles having a particle size distribution of 0.01 μm to 30 μm, the negative electrode active material layer comprising a lower layer portion including a surface facing the negative electrode current collector layer and an upper layer portion including a surface opposite to the surface facing the negative electrode current collector layer, wherein the silicon-based active material contained in the lower layer portion has an average particle size (D50) of 1 μm to 6 μm, the silicon-based active material contained in the upper layer portion has an average particle size (D50) of 7 μm to 15 μm, and the average particle size (D50) of the silicon-based active material contained in the lower layer portion is smaller than the average particle size (D50) of the silicon-based active material contained in the upper layer portion.

[0029] The present invention adjusts the arrangement of the silicon-based active material in the negative electrode active material layer according to the average particle size of the silicon-based active material, and has the main object of having the above-mentioned characteristics to maintain the high capacity characteristics that are an advantage of a negative electrode containing a silicon-based active material, while preventing the electrode from detaching, thereby improving the life characteristics.

[0030] 1 is a diagram showing the laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0031] Specifically, it can be seen that the negative electrode active material layer is formed with a lower layer portion 1-1 including the surface facing the negative electrode current collector layer and an upper layer portion 1-2 including the surface opposite to the surface facing the negative electrode current collector layer. In this case, the thickness of the upper layer and the lower layer may be the same or different.

[0032] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the silicon-based particles include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0033] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the silicon-based particles include at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and the SiOx (x = 0) is included in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material.

[0034] In one embodiment of the present application, there is provided a negative electrode composition, wherein the silicon-based particles include SiOx (x = 0), and the SiOx (x = 0) is included in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material.

[0035] In another embodiment, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0036] In one embodiment of the present application, the silicon-based active material may particularly use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean including pure silicon-based particles (SiOx (x = 0)) that do not combine with other particles or elements within the above range when based on 100 parts by weight of the entire silicon-based active material as described above.

[0037] In one embodiment of the present application, the silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiOx (x = 0).

[0038] 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.

[0039] Therefore, in the present invention, while only a silicon-based active material is used as a negative electrode active material to improve capacity performance, the above-mentioned problems are solved by adjusting the distribution according to the average particle size of the silicon-based active material itself, rather than adjusting the composition of the conductive material and binder.

[0040] In one embodiment of the present application, the silicon-based active material contains silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

[0041] 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 this range, and the number of silicon-based particles contained is not limited.

[0042] The particle size of the silicon-based active material may be expressed as a diameter in the case of a sphere, but even in the case of a shape other than a sphere, the particle size may be measured in comparison with the case of a sphere, and the particle size of each individual silicon-based particle may be measured by a method generally used in the art.

[0043] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 to 150.0 m 2 / g, more preferably 0.1 to 100.0 m 2 / g, particularly preferably 0.2 to 80.0 m 2 / g, most preferably 0.2 to 18.0 m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0044] In one embodiment of the present application, the silicon-based active material may be, for example, in a crystalline or amorphous form, and is preferably not porous.The silicon-based active material is preferably in the form of spherical or shard particles.Alternatively, but less preferably, the silicon-based active material may also have a fibrous structure or be in the form of a silicon-containing film or coating.

[0045] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the silicon-based active material is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0046] In another embodiment, the silicon-based active material may be present in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be present in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0047] The negative electrode for a lithium secondary battery according to the present application has a silicon-based active material having a specific average particle size that can suppress the volume expansion rate during charge and discharge, distributed within the negative electrode, even when a silicon-based active material with an extremely high capacity is used within the above range, and is characterized by excellent output characteristics during charge and discharge without deteriorating the performance of the negative electrode even when the above range is included.

[0048] In one embodiment of the present application, the silicon-based active material may have a non-spherical morphology, and the sphericity thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0049] In this application, the circularity is determined by the following formula 1-1, where A is the area and P is the perimeter. [Formula 1] 4πA / P 2

[0050] While graphite-based compounds have traditionally been used exclusively as anode active materials, attempts to incorporate silicon-based compounds into batteries 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, silicon-based compounds can sometimes experience problems such as rapid volume expansion during charge / discharge processes, damaging the conductive paths formed within the anode active material layer.

[0051] Therefore, in one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of a dot-like conductive material; a sheet-like conductive material; and a linear conductive material.

[0052] In one embodiment of the present application, the dot-like conductive material refers to a spherical or dot-like conductive material that can be used to improve the conductivity of a negative electrode and has conductivity without causing 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.

[0053] 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.

[0054] In one embodiment of the present application, the dot-like conductive material may have a volatile matter content of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0055] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, there are functional groups present on the surface of the dot-shaped conductive material, and when water is used as the solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent.

[0056] In the preparation of dot-like conductive materials, a high functional group content means that there is a lot of foreign matter, and a low functional group content means that more heat treatment processing has been performed.The dot-like conductive material of the present application can satisfy the functional group content range by performing a certain partial heat treatment on the dot-like conductive material in order to satisfy the functional group content range.

[0057] 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.

[0058] In one embodiment of the present application, the negative electrode conductive material may include a sheet conductive material. The planar conductive material refers to a conductive material that increases the surface contact between silicon particles in the negative electrode to improve conductivity and simultaneously prevents the conductive path from being broken due to volume expansion. The planar conductive material may be expressed as a plate-type conductive material or a bulk-type conductive material.

[0059] 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.

[0060] 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 3.5 μm to 5 μm. When the average particle size satisfies this range, the sufficient particle size facilitates dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when dispersing using the same device and time, the dispersion effect is excellent.

[0061] In one embodiment of the present application, the sheet conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 4.0 μm or more and 5.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0062] In one embodiment of the present application, the sheet conductive material may be a high-specific surface area sheet conductive material having a high BET specific surface area; or a low-specific surface area sheet conductive material.

[0063] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material or a low-specific surface area planar conductive material without any restrictions. However, the planar conductive material of the present application 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 planar conductive material that does not cause dispersion problems.

[0064] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0065] 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 5m 2 / g or more 250m 2 / g or less.

[0066] 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.

[0067] 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.

[0068] Other conductive materials may 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 monomers. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in the form of a bundle or rope in which multiple carbon nanotube units are arranged side by side or entangled with their longitudinal axes aligned in substantially the same direction. The carbon nanotube monomer has a graphite sheet in the form of a cylinder with a nanometer-sized diameter and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the bundled carbon nanotubes can 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.

[0069] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a linear conductive material, and the linear conductive material is a carbon nanotube.

[0070] In one embodiment of the present application, the negative electrode conductive material may include a sheet conductive material and a linear conductive material.

[0071] In one embodiment of the present application, the negative electrode conductive material may include a sheet conductive material and a linear conductive material, and the ratio of the sheet conductive material to the linear conductive material may satisfy 1:0.01 to 1:0.1.

[0072] In one embodiment of the present application, the negative electrode composition contains 5 to 40 parts by weight of the negative electrode conductive material based on 100 parts by weight of the negative electrode composition.

[0073] In another embodiment, the negative electrode conductive material may comprise 5 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 15 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0074] 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 excellent output characteristics at a high C-rate.

[0075] The negative electrode conductive material according to the present application has a completely different structure from the conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to form a contact point between silicon-based active materials, which undergo a large volume expansion during charging and discharging, while the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in structure and role from the negative electrode conductive material of the present invention.

[0076] 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 their structure and role are completely different from those of negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0077] 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 negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot-like shape to facilitate the storage and release of lithium ions.

[0078] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape and may be referred to as plate-shaped graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path within the layer, and does not play a role in storing and releasing lithium, but rather serves to ensure a planar conductive path within the negative electrode active material layer.

[0079] 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 contained therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0080] 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 dot-like or spherical shape and is used as a material that stores or releases lithium.

[0081] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is in a dotted form 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 be planar and have a BET specific surface area of ​​5 m 2 / g or more.

[0082] 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.

[0083] 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 deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. 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.

[0084] In one embodiment of the present application, the negative electrode binder may be included in an amount of 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, or may be included in an amount of 5 parts by weight or more, or 10 parts by weight or more.

[0085] 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 is a single-layer negative electrode active material layer, the silicon-based active material contained in the lower layer portion has an average particle size (D50) of 1 μm to 6 μm, and the silicon-based active material contained in the upper layer portion has an average particle size (D50) of 7 μm to 15 μm.

[0086] In another embodiment, the silicon-based active material contained in the lower layer portion may have an average particle size (D50) of 1 μm to 6 μm, and preferably 2 μm to 6 μm.

[0087] In another embodiment, the silicon-based active material contained in the upper layer portion may have an average particle size (D50) of 7 μm to 15 μm, preferably 8 μm to 12 μm.

[0088] As described above, the upper and lower layers contain silicon-based active materials with specific average particle sizes. By satisfying this range, adhesion to the negative electrode current collector layer can be strengthened and the pore structure can be simplified, thereby solving the resistance problem. That is, if the average particle size of the silicon-based active material in the lower layer is less than this range, the silicon-based active material contains fine powder, increasing adhesion but not improving resistance. If the average particle size exceeds this range, the adhesion is reduced, resulting in a decrease in lifespan characteristics. Furthermore, if the average particle size of the silicon-based active material in the upper layer is less than this range, the resistance problem is not solved. If the average particle size exceeds this range, the particle size of the silicon-based active material becomes too large, increasing the volume expansion rate and actually reducing lifespan characteristics.

[0089] In still another embodiment, the negative electrode active material layer comprises a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer comprises the lower layer portion, and the second negative electrode active material layer comprises the upper layer portion, and the silicon-based active material contained in the first negative electrode active material layer has an average particle size (D50) of 1 μm to 6 μm, and the silicon-based active material contained in the second negative electrode active material layer has an average particle size (D50) of 7 μm to 15 μm.

[0090] That is, the negative electrode for a lithium secondary battery according to the present application may include a single layer or a double layer negative electrode active material layer, and the upper layer of the negative electrode active material layer contains a silicon-based active material having a larger average particle size than the lower layer.

[0091] 1, when the negative electrode active material layer 20 is a single layer, the upper layer portion 1-2 and the lower layer portion 1-1 may refer to negative electrode active material layer regions within the single layer. When the negative electrode active material layer 20 is a two-layer layer, the negative electrode active material layer 20 may include a second active material layer including the upper layer portion 1-2 and a first active material layer including the lower layer portion 1-1.

[0092] In one embodiment of the present application, the negative electrode active material layer is a single-layer negative electrode active material layer, and the negative electrode active material layer includes a lower layer portion that includes a surface facing the negative electrode current collector layer.

[0093] When the lower layer portion includes a surface facing the negative electrode current collector layer, there is no limitation on the thickness range thereof, but it may have a thickness of 1% to 60%, preferably 20% to 50%, of the total thickness of the negative electrode active material layer.

[0094] In one embodiment of the present application, the negative electrode active material layer is a single-layer negative electrode active material layer, and the negative electrode active material layer includes an upper layer portion that includes a surface opposite to a surface facing the negative electrode current collector layer.

[0095] When the upper layer portion includes the surface opposite to the surface facing the negative electrode current collector layer, there is no limitation on the thickness range thereof, but the upper layer portion may have a thickness of 20% to 80%, preferably 40% to 70%, of the total thickness of the negative electrode active material layer.

[0096] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the ratio of the thickness of the upper layer portion to the thickness of the lower layer portion is 4:1 to 1.5:1.

[0097] In another embodiment, the ratio of the thickness of the upper layer portion to the thickness of the lower layer portion may be in the range of 4:1 to 1.5:1, preferably 3.5:1 to 1.5:1, and more preferably 3:1 to 1.5:1.

[0098] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, the thickness of the first negative electrode active material layer is 10 μm or more and 250 μm or less, and the thickness of the second negative electrode active material layer is 10 μm or more and 250 μm or less.

[0099] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0100] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. 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 surface can be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer can be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0101] 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.

[0102] 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%.

[0103] 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 first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer to form a second negative electrode active material layer, wherein the first negative electrode active material layer composition and the second negative electrode active material layer composition comprise negative electrode compositions containing a silicon-based active material, a negative electrode conductive material, and a negative electrode binder, the silicon-based active material comprising silicon-based particles having a particle size distribution in the range of 0.01 μm to 30 μm, the silicon-based active material contained in the first negative electrode active material layer composition having an average particle size (D50) of 1 μm to 6 μm, and the silicon-based active material contained in the second negative electrode active material layer composition having an average particle size (D50) of 7 μm to 15 μm.

[0104] In the method for producing the negative electrode, the respective compositions contained in the negative electrode may be the same as those described above.

[0105] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by applying a first negative electrode active material layer slurry and a second negative electrode active material layer slurry containing the first negative electrode active material layer composition and the second negative electrode active material layer composition to one or both surfaces of a negative electrode current collector layer, and drying the applied slurry.

[0106] The first negative electrode active material layer slurry may include the above-described first negative electrode active material layer composition; and a slurry solvent.

[0107] The second negative electrode active material layer slurry may include the second negative electrode active material layer composition described above; and a slurry solvent.

[0108] In one embodiment of the present application, the solid content of the first and second negative electrode active material layer slurries may be 5% or more and 40% or less.

[0109] In another embodiment, the solid content of the first and second negative electrode active material layer slurries may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0110] The solid content of the first and second negative electrode active material layer slurries may refer to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry. When the solid content of the first and second negative electrode active material layer slurries satisfies the above range, the viscosity during the formation of the negative electrode active material layer is appropriate, and particle aggregation of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0111] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry process or a wet-on-wet process.

[0112] In one embodiment of the present application, a wet-on-dry process may refer to a process of applying a first negative electrode active material layer composition (specifically, a first negative electrode active material layer slurry) and then completely drying it, and then applying a second negative electrode active material layer composition (specifically, a second negative electrode active material layer slurry) on top of it. Through this process, the first negative electrode active material layer and the second negative electrode active material layer may have a clear boundary, and therefore the compositions contained in the first negative electrode active material layer and the second negative electrode active material layer may not mix, and the negative electrode active material layer according to the present application may be composed of two layers.

[0113] In one embodiment of the present application, a wet-on-wet process may refer to a process of applying a first negative electrode active material layer composition (e.g., a first negative electrode active material layer slurry) and then applying a second negative electrode active material layer composition (e.g., a second negative electrode active material layer slurry) on top of the first negative electrode active material layer composition before it is completely dried. Through this process, the negative electrode active material layer may be formed as a single-layer negative electrode active material layer having the first negative electrode active material layer composition and the second negative electrode active material layer composition. In this case, some mixing may occur at the interface between the first negative electrode active material layer composition and the second negative electrode active material layer composition, and this mixing at the interface may be referred to as intermixing.

[0114] In one embodiment of the present application, a single-layer negative electrode active material layer or a two-layer negative electrode active material layer may be formed depending on the process conditions for forming the first negative electrode active material layer composition and the second negative electrode active material layer composition as described above.

[0115] 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.

[0116] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are stacked with a separator 30 sandwiched between them.

[0117] 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 and an electrolyte interposed between the positive electrode and the negative electrode, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0118] 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.

[0119] The positive electrode current collector in the positive electrode 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, baked carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0120] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 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 O2 (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≦0.3 is satisfied); 2-c3 M c3Examples include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be lithium metal (Li-metal).

[0121] 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.

[0122] The positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery. Specific examples include graphite such as natural graphite and artificial graphite; carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0123] 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.

[0124] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification capability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0125] 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.

[0126] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0127] 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.

[0128] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred 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 having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and these cyclic carbonates are more preferred.

[0129] The metal salt can 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 can 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:

[0130] 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.

[0131] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and therefore 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]

[0132] In the following, preferred examples are presented to aid in understanding the present invention, but these examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description. Such changes and modifications are naturally intended to fall within the scope of the appended claims.

[0133] <Production example> Example 1 Preparation of first negative electrode active material layer slurry A first negative electrode active material layer composition was formed by mixing Si (average particle size (D50): 5 μm) as a silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10, and adding the resulting mixture to distilled water as a solvent for forming a negative electrode slurry to prepare a first negative electrode slurry.

[0134] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT (single-walled carbon nanotube).

[0135] As a mixing method, 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 and dispersed at 2500 rpm for 30 minutes to prepare a first negative electrode active material layer slurry.

[0136] Preparation of second negative electrode active material layer slurry A second negative electrode active material layer composition was formed using a silicon-based active material, Si (average particle size (D50): 9 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10, and the second negative electrode active material layer composition was added to distilled water as a solvent for forming a negative electrode slurry to prepare a second negative electrode active material layer slurry.

[0137] Thereafter, the first negative electrode active material layer slurry was applied to both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector in an amount of 20 mg / 25 cm. 2At the same time, the second negative electrode slurry was applied on top of it at a loading of 80 mg / 25 cm. 2 The first negative electrode slurry was coated wet-on-wet with a loading of 25%, and the second negative electrode slurry was dried. The solid content of the first negative electrode slurry was 25%, and the solid content of the second negative electrode slurry was 28%.

[0138] Thereafter, the resultant was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a single layer of negative electrode active material layer (thickness: 65 μm), which was used as a negative electrode.

[0139] (Negative electrode thickness: 73 μm, negative electrode porosity: 40%, average particle size (D50) of the lower layer silicon-based active material: 5 μm, average particle size (D50) of the upper layer silicon-based active material: 9 μm)

[0140] <Examples 2 to 10 and Comparative Examples 1 to 10> A negative electrode was prepared in the same manner as in Example 1, except that the average particle size and coating method of the silicon-based active material were changed as shown in Table 1 below.

[0141] [Table 1]

[0142] The experiments in Examples 1 to 10 and Comparative Examples 1 to 10 were based on the distribution of the average particle size of Si particles. Specifically, Examples 1 to 5 correspond to the results of a single-layer active material layer, and Examples 6 to 10 correspond to the results of a double-layer active material layer.

[0143] From the results of Examples 1 to 10, it can be seen that silicon-based active material with a relatively small average particle size is distributed near the negative electrode current collector, which reduces the volume expansion of the active material during charging and discharging, preventing electrode detachment, and that silicon-based active material with a relatively large average particle size is arranged in the upper layer, simplifying the electrode pore structure and thereby reducing the negative electrode resistance.

[0144] That is, in Examples 1 to 10, although the total pore resistance was similar, it was confirmed that the performance difference due to the particle size applied to the bottom and the contact points with the negative electrode current collector increased, and the life characteristics were also improved.

[0145] In Comparative Examples 1 to 5, a single-layer active material layer was formed using a wet-on-wet process. However, similar results were obtained when a wet-on-dry process was used. Therefore, Comparative Examples 6 to 10 are described together with Comparative Examples 1 to 5. Specifically, in Comparative Examples 1 and 2, the particle size of the lower layer was larger than that of the upper layer, and the electrode detachment phenomenon worsened as the absolute value of the volume change in the lower layer increased, resulting in a rapid deterioration in life performance. In Comparative Example 3, the average particle size of the lower layer was maintained smaller than that of the upper layer, but the lower layer was too small. As a result, the lower layer contained fine powder silicon-based active material, which could improve life performance, but the fine powder active material caused a rapid increase in pore resistance, resulting in a decrease in performance.

[0146] In Comparative Example 4, the average particle size of the lower layer was satisfactory, but the average particle size of the upper layer was outside the range of the present application. In this case, detachment from the negative electrode current collector layer could be prevented, but the particle size range of the upper layer was also large, resulting in a large volume expansion coefficient. In this case, detachment between the electrodes occurred, resulting in a rapid deterioration of life performance.

[0147] In the case of Comparative Example 5, neither the average particle size of the lower layer portion nor the average particle size of the upper layer portion was satisfied, and the same results as those of Comparative Examples 1 and 4 were obtained.

[0148] That is, the present invention adjusts the arrangement of the silicon-based active material in the negative electrode active material layer according to the average particle size of the silicon-based active material. By having the above-mentioned characteristics, it is possible to maintain the high capacity characteristics that are the advantages of a negative electrode containing a silicon-based active material, and it has been confirmed through the above experiments that the main characteristics are that the electrode detachment phenomenon can be prevented, an increase in resistance can be prevented, and the life characteristics can also be improved.

[0149] <Experiment on mixed active materials with different particle sizes> A negative electrode active material layer composition was formed by mixing an active material in which Si (average particle size (D50): 5 μm) as a silicon-based active material and Si (average particle size (D50): 9 μm) as a silicon-based active material in the ratios shown in Table 2 below, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10, and adding the resultant to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry.

[0150] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0151] 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 and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode active material layer slurry.

[0152] Thereafter, the negative electrode active material layer slurry was applied to both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector in an amount of 94 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a single layer of negative electrode active material (thickness: 65 μm), which was used as a negative electrode. (Thickness of negative electrode: 73 μm, porosity of negative electrode: 40%)

[0153] [Table 2]

[0154] In Table 2, the mixed particle size ratio refers to the weight ratio of Si (average particle size (D50): 5 μm) as a silicon-based active material and Si (average particle size (D50): 9 μm) as a silicon-based active material based on 100 parts by weight of the total active material.

[0155] The pore resistance (Rpore) was measured depending on the mixing ratio of the negative electrode active materials according to Comparative Examples 11 to 17, and the results are shown in Table 3 below.

[0156] [Table 3]

[0157] As can be seen from Table 3, the pore resistance decreased as the proportion of large particles (D50:9 μm) increased. In other words, simply increasing the proportion of large particles can reduce pore resistance due to lithium ion migration. However, when this proportion was increased infinitely as in Comparative Example 17, the volume expansion of the silicon-based active material caused such poor battery life that it could not be used as a battery. Finally, Table 3 confirms that pore resistance does not have a linear relationship with improved battery life.

[0158] That is, the comparative examples 11 to 17 are related to the use of mixed active materials, and the negative electrode according to the present invention is characterized in that, in addition to improving the pore resistance when using a mixture of active materials having different particle sizes, the lower layer and the upper layer are adjusted and arranged so that the average particle size falls within a specific range.

[0159] Ultimately, it was confirmed through the above experiments that the present invention adjusts the arrangement of the silicon-based active material in the negative electrode active material layer according to the average particle size of the silicon-based active material, and that by having the above characteristics, it is possible to maintain high capacity characteristics, which are advantages of negative electrodes containing silicon-based active materials, while preventing electrode detachment and an increase in resistance, thereby improving life characteristics.

[0160] Furthermore, the present invention preferably includes the following examples. [Section 1] A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on the negative electrode current collector layer, The negative electrode active material layer contains a negative electrode composition including a silicon-based active material, a negative electrode conductive material, and a negative electrode binder. The silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less. The negative electrode active material layer includes a lower layer portion including the surface facing the negative electrode current collector layer and an upper layer portion including the surface opposite to the surface facing the negative electrode current collector layer. The average particle size (D50) of the silicon-based active material contained in the lower layer portion is 1 μm to 6 μm, and the average particle size (D50) of the silicon-based active material contained in the upper layer portion is 7 μm to 15 μm. A negative electrode for a lithium secondary battery, wherein the average particle size (D50) of the silicon-based active material contained in the lower layer portion is smaller than the average particle size (D50) of the silicon-based active material contained in the upper layer portion. [Item 2] The negative electrode active material layer is a single-layer negative electrode active material layer. The negative electrode for a lithium secondary battery according to Item 1, wherein the average particle size (D50) of the silicon-based active material contained in the lower layer portion is 1 μm to 6 μm, and the average particle size (D50) of the silicon-based active material contained in the upper layer portion is 7 μm to 15 μm. [Item 3] The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer. The first negative electrode active material layer includes the lower layer portion. The second negative electrode active material layer includes the upper layer portion. The negative electrode for a lithium secondary battery according to Item 1, wherein the average particle size (D50) of the silicon-based active material contained in the first negative electrode active material layer is 1 μm to 6 μm, and the average particle size (D50) of the silicon-based active material contained in the second negative electrode active material layer is 7 μm to 15 μm. [Item 4] The negative electrode for a lithium secondary battery according to Item 1, wherein the silicon-based particles include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 <x <2), SiC, and Si alloys. [Item 5] The silicon-based particles include at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and contain 70 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. The negative electrode for a lithium secondary battery according to Item 1. [Item 6] The silicon-based active material is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition. The negative electrode for a lithium secondary battery according to Item 1. [Item 7] The negative electrode conductive material includes a planar conductive material and a linear conductive material. The negative electrode for a lithium secondary battery according to Item 1. [Item 8] The ratio of the thickness of the upper layer part to the thickness of the lower layer part is 4:1 to 1.5:1. The negative electrode for a lithium secondary battery according to Item 1. [Item 9] The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less. The thickness of the first negative electrode active material layer is 10 μm or more and 250 μm or less. The thickness of the second negative electrode active material layer is 10 μm or more and 250 μm or less. The negative electrode for a lithium secondary battery according to Item 3. [Item 10] A step of preparing a negative electrode current collector layer. A step of applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer, and A step of applying a second negative electrode active material layer composition to the opposite surface of the first negative electrode active material layer that contacts the negative electrode current collector layer to form a second negative electrode active material layer. A method for manufacturing a negative electrode for a lithium secondary battery, including The first negative electrode active material layer composition and the second negative electrode active material layer composition include a negative electrode composition containing a silicon-based active material, a negative electrode conductive material, and a negative electrode binder. The silicon-based active material includes silicon-based particles having a particle size distribution range of 0.01 μm or more and 30 μm or less. a silicon-based active material contained in the first negative electrode active material layer composition having an average particle size (D50) of 1 μm to 6 μm, and a silicon-based active material contained in the second negative electrode active material layer composition having an average particle size (D50) of 7 μm to 15 μm; [Section 11] Item 11. The method for manufacturing a negative electrode for a lithium secondary battery according to item 10, wherein the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry process or a wet-on-wet process. [Section 12] positive electrode, Item 10. The negative electrode for a lithium secondary battery according to any one of items 1 to 9. a separator provided between the positive electrode and the negative electrode; and electrolyte, A lithium secondary battery comprising: [Explanation of symbols]

[0161] 1-1...Lower part 1-2 Upper Management 10 Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on the negative electrode current collector layer, the negative electrode active material layer includes a negative electrode composition including a silicon-based active material, a negative electrode conductive material, and a negative electrode binder, the silicon-based active material including silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less; the negative electrode active material layer includes a lower layer portion including a surface facing the negative electrode current collector layer and an upper layer portion including a surface opposite to the surface facing the negative electrode current collector layer, The silicon-based active material contained in the lower layer portion has an average particle size (D50) of 1 μm to 6 μm, and the silicon-based active material contained in the upper layer portion has an average particle size (D50) of 7 μm to 15 μm.

2. The negative electrode for a lithium secondary battery according to claim 1 , wherein the negative electrode active material layer is a single layer.

3. the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer includes the lower layer portion, the second negative electrode active material layer includes the upper layer portion, 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material contained in the first negative electrode active material layer has an average particle size (D50) of 1 μm to 6 μm, and the silicon-based active material contained in the second negative electrode active material layer has an average particle size (D50) of 7 μm to 15 μm.

4. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based particles include at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and a Si alloy.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based particles include at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and the silicon-based particles include 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

6. The negative electrode for a lithium secondary battery according to claim 1 , wherein the silicon-based active material is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

7. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode conductive material comprises a sheet conductive material and a linear conductive material.

8. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein a ratio of the thickness of the upper layer portion to the thickness of the lower layer portion is 4:1 to 1.5:

1.

9. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, the thickness of the first negative electrode active material layer is 10 μm or more and 250 μm or less; The negative electrode for a lithium secondary battery according to claim 3 , wherein the second negative electrode active material layer has a thickness of 10 μm to 250 μm.

10. providing a negative electrode current collector layer; forming a first negative electrode active material layer by applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer; and forming a second negative electrode active material layer by applying a second negative electrode active material composition to a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer; A method for producing a negative electrode for a lithium secondary battery, comprising: the first negative electrode active material layer composition and the second negative electrode active material layer composition each include a negative electrode composition including a silicon-based active material, a negative electrode conductive material, and a negative electrode binder, the silicon-based active material including silicon-based particles having a particle size distribution in the range of 0.01 μm to 30 μm, a silicon-based active material contained in the first negative electrode active material layer composition having an average particle size (D50) of 1 μm to 6 μm, and a silicon-based active material contained in the second negative electrode active material layer composition having an average particle size (D50) of 7 μm to 15 μm.

11. 11. The method of claim 10, wherein forming the second negative electrode active material layer on the first negative electrode active material layer comprises a wet-on-dry process or a wet-on-wet process.

12. positive electrode, The negative electrode for a lithium secondary battery according to any one of claims 1 to 9, a separator provided between the positive electrode and the negative electrode; and electrolyte, A lithium secondary battery comprising:

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