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

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, a method for manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode, the lithium secondary battery having a double-layer structure with a specific composition, and having an adjustable thickness range, which enables rapid charging of an electrode using a high content of Si particles as a single-layer active material, and at the same time, has the advantage of being able to solve the problems of surface deterioration, uniformity during pre-lithiation, and life characteristics, which are disadvantages of the electrode.

Description

[Technical Field]

[0001] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0086772, filed with the Korean Intellectual Property Office on 14 July 2022, and all its contents are incorporated herein by reference.

[0002] This 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. [Background technology]

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

[0004] Currently, a typical example of an electrochemical element that utilizes this type of electrochemical energy is the secondary battery, and its range of applications is steadily expanding.

[0005] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly growing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, research is actively underway on methods for manufacturing high-density electrodes with even higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

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

[0007] In recent years, in response to the demand for high-density energy batteries, research has been actively conducted on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx, which have more than 10 times the capacity of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds are high-capacity materials and have superior capacity characteristics compared to conventionally used graphite, they rapidly expand in volume during the charging process, disrupting the conductive path and degrading battery performance, resulting in a decrease in capacity from the start. Furthermore, with silicon-based negative electrodes, uniform charging of lithium ions does not occur in the depth direction of the negative electrode during repeated charge and discharge cycles, and the reaction proceeds at the surface, accelerating surface degradation. Therefore, performance improvements are needed in terms of battery cycles.

[0008] While graphite electrodes exhibit superior lifespan characteristics compared to silicon-based electrodes, they suffer from inferior rapid charging performance. In recent years, as lithium-ion batteries have become more widely used, research has progressed to shorten the charging time for lithium-ion batteries, requiring that charging be completed within at least 20 minutes. To improve rapid charging performance, silicon-based negative electrodes with high relative capacity and potential compared to graphite are used. However, silicon-based negative electrodes exhibit the aforementioned problems due to structural changes and breakdown caused by high capacity. When silicon-based and graphite-based electrodes are mixed, the structure of the graphite electrode also breaks down, resulting in a significant decrease in lifespan characteristics.

[0009] Therefore, in order to resolve the aforementioned problems when using silicon-based compounds, which have excellent rapid charging performance, as negative electrode active materials on their own, various methods are being discussed, such as methods to adjust the driving potential, methods to further coat a thin film on the active material layer, methods to suppress volume expansion itself such as adjusting the particle size of the silicon-based compound, or the development of a binder that suppresses the volume expansion of the silicon-based compound to prevent the conduction path from being interrupted.

[0010] However, the aforementioned method may actually degrade battery performance, thus limiting its applicability. There are still limitations to the commercialization of negative electrode batteries with a high content of silicon-based compounds that offer superior rapid charging performance. As the proportion of silicon-based active material in the silicon-based active material layer increases, prelithiation concentrates on the negative electrode surface, leading to damage to the silicon-based active material on the surface and uneven prelithiation, which poses problems in improving lifespan characteristics.

[0011] Therefore, in order to improve the rapid charging performance of lithium secondary batteries, research is needed on lithium secondary batteries that use silicon-based anodes, which are high-capacity materials, and that can also ensure their lifespan characteristics. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0013] In this application, we have confirmed through research that by using a carbon-based active material as the negative electrode and coating it with a silicon-based composition, which is a high-capacity material, within the range of Formula 1 described later, to form a silicon-based buffer layer, it is possible to ensure the rapid charging performance, which is a problem with conventional methods, and furthermore, improve both capacity characteristics and cycle performance. Accordingly, this 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 the negative electrode. [Means for solving the problem]

[0014] One embodiment of the present specification is a negative electrode for a lithium secondary battery including a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer, wherein the first negative electrode active material layer includes a first negative electrode active material layer composition containing a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material layer composition containing a second negative electrode active material, the second negative electrode active material layer includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and SiC, the first negative electrode active material includes one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and based on 100 parts by weight of the first negative electrode active material, the silicon-based active material is contained in an amount of 5 parts by weight or less, and a negative electrode for a lithium secondary battery satisfying the following formula 1 is provided. [Formula 1] 0.1 ≦ [B / (A + B)] × 100 (%) ≦ 15

[0015] In Formula 1, A is the total thickness of the first negative electrode active material layer, which is 30 μm or more and 150 μm or less, B is the total thickness of the second negative electrode active material layer.

[0016] In another embodiment, a method for manufacturing a negative electrode for a lithium secondary battery includes 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 the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer to form a second negative electrode active material layer, wherein the second negative electrode active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and SiC, the first negative electrode active material includes one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and based on 100 parts by weight of the first negative electrode active material, the silicon-based active material is contained in an amount of 5 parts by weight or less, and a method for manufacturing a negative electrode for a lithium secondary battery satisfying the formula 1 is provided.

[0017] Finally, provided is a lithium secondary battery including a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

Advantages of the Invention

[0018] The negative electrode for a lithium secondary battery according to one embodiment of the present invention has a double-layer active material layer composed of a first negative electrode active material layer and a second negative electrode active material layer. In particular, the second negative electrode active material contained in the second negative electrode active material layer includes at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and SiC.

[0019] At this time, by satisfying the thickness within the range of Formula 1 for the second negative electrode active material layer of the negative electrode for a lithium secondary battery according to the present application, the rapid charging performance can be maximized by thinly coating the second negative electrode active material layer having high-capacity characteristics. The precipitation of lithium due to rapid charging, which is a conventional problem, will occur due to the graphite-based active material whose potential becomes negative by charging at a high C-rate, but it has a feature capable of solving such a problem.

[0020] Further, the first negative electrode active material may include one or more selected from the group consisting of a carbon-based active material, SiOx (0 < x < 2), SiC, and Si alloy, and particularly may include a carbon-based active material and SiOx (0 < x < 2).

[0021] In other words, in the lithium secondary battery anode according to this application, since the second anode active material layer is located at the uppermost end, lithium deposition by the graphite-based active material described above is formed between the first anode active material layer and the second anode active material layer. This suppresses the formation of lithium dendrites on the surface of the anode, eliminating the short-circuit problem, and because the silicon potential is high, lithium moves smoothly to the second anode active material layer. In conclusion, the lithium secondary battery anode according to this application has a double-layer structure with a specific composition, and its thickness range is adjusted to the range of Equation 1, resulting in a very low probability of problems occurring due to lithium deposition.

[0022] In short, the negative electrode for lithium secondary batteries according to this application is characterized by adopting the advantages of rapid charging of electrodes that use a high content of Si particles as a single layer active material, while solving the problems of surface degradation, uniformity during pre-lithiation, and life characteristics that are drawbacks of such electrodes, by constructing the first negative electrode active material layer and the second negative electrode active material layer in a double layer configuration and applying a specific composition and thickness. [Brief explanation of the drawing]

[0023] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0024] Before describing the present invention, let us first define some terms.

[0025] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0026] In this specification, "p~q" means the range "p or greater and q or less".

[0027] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mini II from BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0028] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the particle size distribution can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size as the particles pass through the laser beam is measured to calculate the particle size distribution.

[0029] In this specification, when a polymer contains a monomer as a monomer unit, it means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer contains a monomer, this is interpreted as meaning that the polymer contains monomers as monomer units.

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

[0031] In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are the molecular weights in terms of polystyrene measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available as standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0032] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention pertains to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0033] One embodiment of this specification is a negative electrode for a lithium secondary battery including a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the surface of the first negative electrode active material layer that contacts the negative electrode current collector layer. The first negative electrode active material layer includes a first negative electrode active material layer composition containing a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material layer composition containing a second negative electrode active material, the second negative electrode active material layer includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and SiC, the first negative electrode active material includes one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and based on 100 parts by weight of the first negative electrode active material, the silicon-based active material is contained in an amount of 5 parts by weight or less and satisfies Formula 1, and a negative electrode for a lithium secondary battery is provided.

[0034] This application is obtained by coating a silicon-based active material layer having a range of Formula 1 on the upper layer of a carbon-based negative electrode in order to ensure the rapid charging performance, which is a shortcoming of existing carbon-based negative electrodes. The first negative electrode active material layer (lower layer) serves to suppress the volume expansion of the second negative electrode active material layer (upper layer), and the second negative electrode active material layer (upper layer) serves to ensure the rapid charging performance.

[0035] In this case, the first negative electrode active material layer (lower layer) mainly consists of carbon-based active material, and in order to ensure capacity characteristics, it is necessary to use a mixture of silicon-based active material as described in the application, to the extent that it does not cause problems with lifespan performance, and it is important to use it within a thickness range (A) that can suppress volume expansion. Furthermore, the second negative electrode active material layer (upper layer) must be coated with a thickness that satisfies a certain range (Equation 1) relative to the total negative electrode thickness in order to ensure both rapid charging and lifespan performance.

[0036] The negative electrode for lithium secondary batteries according to this application has a double-layer structure with a specific composition, and its thickness range is adjusted to the range of Equation 1, which significantly reduces the probability of problems occurring due to lithium deposition.

[0037] Figure 1 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a first negative electrode active material layer 20 and a second negative electrode active material layer 10 on one surface of a negative electrode current collector layer 30. Figure 1 shows that the first negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode current collector layer.

[0038] The negative electrode for lithium secondary batteries of the present invention will be described in more detail below.

[0039] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the side of the first negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer.

[0040] 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, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0041] In one embodiment of the present application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less. More preferably, it may be 1 μm or more and 80 μm or less, and even more preferably, it may be 1 μm or more and 20 μm or less.

[0042] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0043] In one embodiment of the present application, the second negative electrode active material may include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and SiC.

[0044] In one embodiment of the present application, the second negative electrode active material may be SiOx (0 < x < 2).

[0045] In one embodiment of the present application, the second negative electrode active material may be SiC.

[0046] In one embodiment of the present application, the second negative electrode active material includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the second negative electrode active material, the SiOx (x = 0) is contained in 95 parts by weight or more, preferably 97 parts by weight or more, and even more preferably 99 parts by weight or more, and may be contained in 100 parts by weight or less.

[0047] In one embodiment of this application, the second negative electrode active material may be pure silicon (Si) particles. Using pure silicon (Si) as the second negative electrode active material means that, based on 100 parts by weight of the total first negative electrode active material, it includes pure Si particles (SiOx(x=0)) that are not bonded with other particles or elements within the range described above.

[0048] The second negative electrode active material used in the second negative electrode active material layer of the present invention undergoes a very complex crystallographic change in the reaction of electrochemically absorbing, storing, and releasing lithium atoms. As the reaction of electrochemically absorbing, storing, and releasing lithium atoms progresses, the composition and crystal structure of silicon particles change to Si (crystal structure: Fd3m), LiSi (crystal structure: I41 / a), Li2Si (crystal structure: C2 / m), Li7Si2 (Pbam), Li 22 It transforms into Si5(F23), etc. Furthermore, along with the complex changes in crystal structure, the volume of silicon particles expands by approximately four times. Therefore, repeated charge-discharge cycles can cause the silicon particles to break down, and as bonds form between lithium atoms and silicon particles, the insertion sites for lithium atoms that the silicon particles initially possessed are damaged, potentially leading to a significant decrease in cycle life.

[0049] In one embodiment of this application, the second negative electrode active material may be SiOx (x=0).

[0050] The second negative electrode active material layer according to this application contains a second negative electrode active material, specifically containing pure silicon particles comprising 95 parts by weight or more of SiOx (x=0). In this case, when pure silicon particles are included in a high content, excellent capacity characteristics can be achieved.

[0051] On the one hand, the average particle size (D50) of the second negative electrode active material of the present invention is 3 μm to 10 μm, specifically 4 μm to 8 μm, and more specifically may be 5 μm to 7 μm. When the average particle size is included in the above range, the specific surface area of the particles is included in an appropriate range, and the viscosity of the negative electrode slurry is formed in an appropriate range. As a result, the dispersion of the particles constituting the negative electrode slurry becomes smooth. Further, since the size of the first negative electrode active material has a value not less than the lower limit value range, the contact area between the silicon particles and the conductive material by the composite composed of the conductive material and the binder in the negative electrode slurry is excellent, and the possibility of the conductive network continuing is increased, and the capacity retention rate increases. On the other hand, when the average particle size satisfies the above range, silicon particles that are too large are excluded, and the surface of the negative electrode is smoothly formed, thereby preventing the current density non-uniformity phenomenon during charge and discharge.

[0052] In one embodiment of the present application, the second negative electrode active material has a generally characteristic BET surface area. The BET surface area of the first negative electrode active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET surface area is measured in accordance with DIN661{31} (using nitrogen).

[0053] In one embodiment of the present application, the second negative electrode active material can exist, for example, in a crystalline or amorphous form and is preferably not porous. The silicon particles are preferably spherical or flaky particles. As an alternative, although less preferred, the silicon particles may have a fibrous structure or may exist in the form of a silicon-containing film or coating.

[0054] In one embodiment of this application, the second negative electrode active material may have a non-spherical shape, and its degree of sphericity is, for example, 0.9 or less, for example 0.7 to 0.9, for example 0.8 to 0.9, for example 0.85 to 0.9.

[0055] In this application, the degree of sphericity is determined by the following formula 1-1, where A' is the area and P is the boundary line. [Formula 1-1] 4πA' / P 2

[0056] In one embodiment of this application, the negative electrode for a lithium secondary battery is provided, wherein the second negative electrode active material is 60 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition.

[0057] In another embodiment, the second negative electrode active material may be 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 80 parts by weight or less, based on 100 parts by weight of the second negative electrode active material layer composition.

[0058] The second negative electrode active material layer composition according to this application can minimize surface degradation by using a second negative electrode active material layer within the thickness range described later, even when using a second negative electrode active material with significantly high capacity within the aforementioned range, and also has the characteristic of having excellent rapid charging performance.

[0059] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, silicon-based compounds have a limitation: their volume expands rapidly during the charge / discharge process, damaging the conductive paths formed within the negative electrode active material layer and actually degrading the battery's performance.

[0060] Accordingly, in one embodiment of the present application, the second negative electrode active material layer composition may further include at least one selected from the group consisting of a second negative electrode conductive material and a second negative electrode binder.

[0061] In this case, the second negative electrode conductive material and the second negative electrode binder included in the second negative electrode active material layer composition may be those commonly used in the industry and can be used without limitation.

[0062] In one embodiment of this application, the second negative electrode conductive material can be any material commonly used in the industry, and may specifically include at least one selected from the group consisting of point conductive materials; planar conductive materials; and linear conductive materials.

[0063] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity to the negative electrode, possesses conductivity without inducing chemical changes, and means a conductive material having point-like or spherical shapes. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and may preferably include carbon black in that it embodies high conductivity and has excellent dispersibility.

[0064] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 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 It may be less than / g.

[0065] In one embodiment of this application, the particle size of the dot-like conductive material is 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0066] In one embodiment of this application, the second negative electrode conductive material may include a planar conductive material.

[0067] The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. It can be described as a plate-type conductive material or a bulk-type conductive material.

[0068] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0069] In one embodiment of this application, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is met, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same apparatus and time, the dispersion effect is excellent.

[0070] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0071] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material.

[0072] In one embodiment of this application, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation as the planar conductive material. In particular, the planar conductive material according to this 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.

[0073] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​5 m². 2 It may be more than / g.

[0074] In another embodiment, the planar conductive material has a BET specific surface area of ​​5 m². 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 It may be less than / g.

[0075] In another embodiment, the planar conductive material is a high specific surface area planar conductive material with a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80mg 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0076] In another embodiment, the planar conductive material is a low specific surface area planar conductive material with a BET specific surface area of ​​5 m². 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 The range of / g or less may also be satisfied.

[0077] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in the form of a bundle or rope, in which multiple carbon nanotube units are arranged in substantially the same orientation along their longitudinal axes, or are intertwined. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be determined by the angle and structure in which the graphite sheet is wound. Compared to entangled type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during anode manufacturing, smoothly form a conductive network within the anode, and improve the conductivity of the anode.

[0078] In particular, the linear conductive material according to one embodiment of this application may be a single-walled carbon nanotube (SWCNT).

[0079] The aforementioned single-walled carbon nanotube is a material in which carbon atoms arranged in a hexagonal pattern form a tube. Depending on its unique chirality, it exhibits properties as an insulator, a fully conductive or semiconductor. The carbon atoms are linked by strong covalent bonds, resulting in a tensile strength approximately 100 times greater than that of steel, excellent flexibility and elasticity, and chemically stable properties.

[0080] The average diameter of the single-walled carbon nanotubes is 0.5 nm to 15 nm. According to one embodiment of the present invention, the average diameter of the single-walled carbon nanotubes may be 1 to 10 nm, or 1 nm to 5 nm, or 1 nm to 2 nm. When the average diameter of the single-walled carbon nanotubes satisfies such a range, the electrical conductivity of the negative electrode can be maintained even if single-walled carbon nanotubes are included in a very small amount, and a desirable viscosity and solid content can be obtained when manufacturing the conductive material dispersion. In the conductive material dispersion, the single-walled carbon nanotubes may exist in an entangled state (aggregates) where they are intertwined with each other. Therefore, the average diameter can be derived by first confirming the diameter of any entangled single-walled carbon nanotube aggregate extracted from the conductive material dispersion using SEM or TEM, and then dividing the diameter of the aggregate by the number of single-walled carbon nanotubes constituting the aggregate.

[0081] The BET specific surface area of ​​the single-walled carbon nanotube is 500 m². 2 / g~1,500m 2 / g, or 900m 2 / g~1,200m 2 It is / g, specifically 250m 2 / g~330m 2 It may also be / g. When the above range is met, a conductive material dispersion having a desirable solid content is dispensed, and the viscosity of the negative electrode slurry is prevented from increasing excessively. The BET specific surface area can be measured by the nitrogen adsorption BET method.

[0082] The aspect ratio of the single-walled carbon nanotube may be 50 to 20,000, or the length of the single-walled carbon nanotube may be 5 μm to 100 μm, or 5 μm to 50 μm. When the aspect ratio or length satisfies such a range, the specific surface area is at a high level, allowing the single-walled carbon nanotube to be strongly adsorbed to the active material particles within the negative electrode. This allows the conductive network to be smoothly maintained even with volume expansion of the negative electrode active material. The aspect ratio can be confirmed by observing the single-walled carbon nanotube powder through an SEM and calculating the average of the aspect ratios of 15 single-walled carbon nanotubes with a high aspect ratio and 15 single-walled carbon nanotubes with a low aspect ratio.

[0083] Compared to multi-walled and double-walled carbon nanotubes, the single-walled carbon nanotubes have an advantage in that they have a larger aspect ratio, longer length, and larger volume, allowing them to construct electrical networks even when used in small quantities.

[0084] In one embodiment of this application, the second negative electrode conductive material may be 1 part by weight or more and 40 parts by weight or less, based on 100 parts by weight of the second negative electrode active material layer composition.

[0085] In another embodiment, the second negative electrode conductive material may be 1 to 40 parts by weight, preferably 3 to 30 parts by weight, and more preferably 3 to 15 parts by weight, based on 100 parts by weight of the second negative electrode active material layer composition.

[0086] In one embodiment of this application, the second negative electrode conductive material includes a point conductive material; a planar conductive material; and a linear conductive material, wherein the ratio of the point conductive material:planar conductive material:linear conductive material may satisfy a ratio of 1:1:0.01 to 1:1:1.

[0087] In one embodiment of this application, the point conductive material may be in an amount of 1 to 60 parts by weight, preferably 5 to 50 parts by weight, and more preferably 10 to 50 parts by weight, based on 100 parts by weight of the second negative electrode conductive material.

[0088] In one embodiment of this application, the planar conductive material may be in the range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the second negative electrode conductive material.

[0089] In one embodiment of this application, the linear conductive material may be in an amount of 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 8 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 second negative electrode conductive material.

[0090] In one embodiment of this application, the second negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0091] In one embodiment of this application, the second negative electrode conductive material includes a linear conductive material and a planar conductive material, and the ratio of the linear conductive material to the planar conductive material may satisfy 0.01:1 to 0.1:1.

[0092] In one embodiment of this application, the second negative electrode conductive material particularly includes a linear conductive material and a planar conductive material, and by satisfying the above composition and proportion, the number of points where charging and discharging are possible increases without significantly affecting the life characteristics of existing lithium secondary batteries, and the battery has the characteristic of having excellent output characteristics at a high C-rate.

[0093] The present application provides a negative electrode for a lithium secondary battery, wherein the second negative electrode conductive material includes at least a linear conductive material.

[0094] In one embodiment of this application, the second negative electrode conductive material may be a linear conductive material.

[0095] In this case, the amount of the linear conductive material may be 0.1 to 2 parts by weight, 0.1 to 0.7 parts by weight, or 0.1 to 0.3 parts by weight, based on 100 parts by weight of the second negative electrode active material. When the content of the linear conductive material satisfies such a range, an electrical network can be sufficiently constructed within the negative electrode active material layer, which is advantageous in terms of mixing and coating processability during electrode manufacturing. Furthermore, in a negative electrode according to one embodiment of the present invention, since the linear conductive material is included in both the first negative electrode active material layer and the second negative electrode active material layer, the conductive network between the active materials can be maintained in accordance with the volume expansion and contraction of the Si electrode, which is advantageous in terms of lifespan and enables the maintenance of rapid charging performance. Basically, rapid charging performance is advantageous for Si-based negative electrodes because thin film coating is possible compared to graphite, and the linear conductive material helps in rapid charging by robustly maintaining the conductive network, and further helps in improving the initial sharp decline in lifespan of the Si-based negative electrode and maintaining its lifespan.

[0096] In the case of the second negative electrode conductive material of this application, it has a completely different configuration from the positive electrode conductive material applied to the positive electrode. That is, in the case of the second negative electrode conductive material of this application, it plays the role of capturing the contact points between silicon-based active materials, where the volume expansion of the electrodes is very large due to charging and discharging, while the positive electrode conductive material plays the role of a buffer that has a cushioning function when rolled and imparts some conductivity, and its configuration and role are completely different from the negative electrode conductive material of the present invention.

[0097] Furthermore, the second negative electrode conductive material in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have smaller particles compared to the active material, thus providing improved output characteristics and partial conductivity. Their structure and role are completely different from the first negative electrode conductive material applied together with silicon-based active materials, as in the present invention.

[0098] In one embodiment of this application, the second negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these substances are substituted with Li, Na, or Ca, or may contain various copolymers thereof.

[0099] The second negative electrode binder according to one embodiment of this application plays a role in suppressing the active material and conductive material in order to prevent twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the second negative electrode active material. Any general binder can be applied as long as it satisfies the above role, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0100] In one embodiment of this application, the second negative electrode binder is 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the second negative electrode active material layer composition, and may be 1 part by weight or more, or 5 parts by weight or more.

[0101] Compared to the first negative electrode active material layer described later, the second negative electrode binder is present at a higher level, which can strongly suppress the first negative electrode active material layer and have the effect of suppressing the volume expansion of the silicon-based active material contained in the first negative electrode active material layer.

[0102] In one embodiment of the present application, the first negative electrode active material includes at least one selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride, and based on 100 parts by weight of the first negative electrode active material, the silicon-based active material is included in an amount of 5 parts by weight or less.

[0103] At this time, based on 100 parts by weight of the first negative electrode active material, the silicon-based active material may be 1 part by weight or more and 5 parts by weight or less.

[0104] The first negative electrode active material layer (lower layer portion) is mainly composed of a carbon-based active material. In order to ensure capacity characteristics, it is necessary to mix and use a silicon-based active material as in the present application so as not to cause problems in life performance, and it is important to use it in a thickness range (A) that can suppress volume expansion.

[0105] In one embodiment of the present application, the first negative electrode active material may include a carbon-based active material and a mixed composition of a silicon-based active material.

[0106] In one embodiment of the present application, the silicon-based active material included in the first negative electrode active material may include at least one selected from the group consisting of SiOx (0 < x < 2), SiC, and Si alloy.

[0107] In one embodiment of the present application, the silicon-based active material provides a negative electrode for a lithium secondary battery including SiOx (0 < x < 2) or SiC.

[0108] In another embodiment, the silicon-based active material included in the first negative electrode active material may include SiOx (0 < x < 2).

[0109] In another embodiment, the silicon-based active material included in the first negative electrode active material may include SiC.

[0110] The negative electrode for lithium secondary batteries according to this application is composed of a double layer, and as described above, the first negative electrode active material layer contains the first negative electrode active material. Specifically, a carbon-based active material is used as the main active material, and a silicon-based active material may be used or omitted, resulting in an overall enhanced electrode lifespan characteristic. Furthermore, the problem of rapid charging is solved by including the second negative electrode active material layer described above.

[0111] In one embodiment of this application, the carbon-based active material can be any carbon material commonly used for lithium secondary batteries, such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, or activated carbon. Specifically, it may be processed into spherical or dot-like forms for use.

[0112] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the carbon-based active material contains graphite, the graphite contains artificial graphite and natural graphite, and the weight ratio of the artificial graphite to the natural graphite is 5:5 to 9.5:0.5.

[0113] The artificial graphite according to one embodiment of the present invention may be in the form of primary particles, or in the form of secondary particles formed by the aggregation of multiple primary particles.

[0114] As used in this invention, the term "initial particle" refers to the original particle from which other types of particles are formed, and multiple primary particles can be aggregated, combined, or assembled to form secondary particles.

[0115] As used in this invention, the term "secondary particles" refers to larger, physically separable particles formed by the aggregation, bonding, or assembly of individual primary particles.

[0116] The aforementioned primary particles of artificial graphite may be produced by heat-treating one or more selected from the group consisting of needle coke, mosaic coke, and coal tar pitch.

[0117] The aforementioned artificial graphite is generally produced by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum-based heavy oil at temperatures above 2,500°C. After graphitization, it can be used as a negative electrode active material after adjusting the particle size through processes such as pulverization and secondary particle formation. In the case of artificial graphite, the crystals are randomly distributed within the particles, resulting in a lower degree of spheroidization and a somewhat pointed shape compared to natural graphite.

[0118] The artificial graphite used in one embodiment of the present invention may include commercially widely used MCMB (mesophase carbon microbeads), MPCF (mesophase pitch-based carbon fiber), graphitized artificial graphite in block form, or graphitized artificial graphite in powder form. The sphericity of the artificial graphite may be 0.91 or less, or 0.6 to 0.91, or 0.7 to 0.9.

[0119] Furthermore, the artificial graphite may have a particle size of 5 to 30 μm, preferably 10 to 25 μm.

[0120] Specifically, the D50 of the artificial graphite primary particles is 6 μm to 15 μm, or it may be 6 μm to 10 μm, or it may be 6 μm to 9 μm. When the D50 of the primary particles satisfies such a range, the primary particles can be formed to a degree of high graphitization, and the orientation index of the negative electrode active material particles can be appropriately ensured, thereby improving the rapid charging performance.

[0121] The artificial graphite secondary particles may be formed by assembling primary particles. That is, the secondary particles may be structures formed by the aggregation of the primary particles through an assembly process. The secondary particles may include a carbonaceous matrix that aggregates the primary particles. The carbonaceous matrix may include at least one of soft carbon and graphite. The soft carbon may be formed by heat-treating pitch.

[0122] The carbonaceous matrix may be present in the secondary particles in an amount of 8% to 16% by weight, specifically 9% to 12% by weight. This range is lower than the carbonaceous matrix content typically used in secondary particles of artificial graphite. This allows for control of the particle size of the primary particles within the secondary particles, enabling the production of structurally stable secondary particles even with a small amount of carbonaceous matrix required for assembly, and ensuring a uniform amount of primary particles constituting the secondary particles.

[0123] The artificial graphite secondary particles have a carbon coating layer on their surface, and the carbon coating layer may contain at least one of amorphous carbon and crystalline carbon.

[0124] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene and graphene.

[0125] The amorphous carbon can adequately maintain the strength of the coating layer and suppress the expansion of the natural graphite. The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source in chemical vapor deposition.

[0126] The aforementioned carbides of other organic substances may be carbides of organic substances selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or kedohexose, and combinations thereof.

[0127] The D50 of the artificial graphite secondary particles is 10 μm to 25 μm, specifically 12 μm to 22 μm, and more specifically 13 μm to 20 μm. When this range is met, the artificial graphite secondary particles can be uniformly dispersed in the slurry, and the battery charging performance can also be improved.

[0128] The tap density of the artificial graphite secondary particles is 0.85 g / cc to 1.30 g / cc, more specifically 0.90 g / cc to 1.10 g / cc, and more specifically 0.90 g / cc to 1.07 g / cc. When this range is met, it means that the packing of the artificial graphite secondary particles can be carried out smoothly within the negative electrode, and thus the adhesion strength of the negative electrode can be improved.

[0129] The aforementioned natural graphite may generally exist as plate-like aggregates before processing, and these plate-like particles can be manufactured into a spherical form with a smooth surface by post-processing such as particle crushing and reassembly processes for use as an active material for electrode manufacturing.

[0130] The natural graphite used in one embodiment of the present invention may have a sphericity greater than 0.91 and 0.97 or less, or 0.93 to 0.97, or 0.94 to 0.96.

[0131] The aforementioned natural graphite may have a particle size of 5 μm to 30 μm, or 10 μm to 25 μm.

[0132] According to one embodiment of the present invention, the weight ratio of artificial graphite to natural graphite may be 5:5 to 9.5:0.5, or 5:5 to 9.3:0.7, or 5:5 to 9:1, or 6:4 to 9:1. When the weight ratio of artificial graphite to natural graphite falls within such a range, it may exhibit superior output and be advantageous in terms of lifespan and fast charging performance.

[0133] In one embodiment of this application, the planar conductive material used as the negative electrode conductive material described above has a different structure and role from carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form for use in order to facilitate the storage and release of lithium ions.

[0134] On the other hand, planar conductive materials used as negative electrode conductive materials are substances that have a planar or plate-like form and can be described as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0135] In other words, the use of plate-shaped graphite as a conductive material in this application means that it was used not to store or release lithium after being processed into a planar or plate-shaped form, but rather as a material that secures a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0136] On the other hand, in this application, the use of a carbon-based active material as an active material means that it was processed into a point-like or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0137] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, has a BET specific surface area of ​​0.1 m².2 / g or more 4.5m 2 The range of less than or equal to / g may also be satisfied. In addition, plate-type graphite, which is a planar conductive material, has a planar BET specific surface area of ​​5m². 2 It may be more than / g.

[0138] The aforementioned metallic active material may be a compound containing one or more metallic elements selected from the group consisting of Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, Sb, Ga, Mn, Fe, Co, Ni, Cu, Sr, and Ba, as a representative example. These metallic compounds can be used in any form, such as elements, alloys, oxides (TiO2, SnO2, etc.), nitrides, sulfides, borides, or alloys with lithium, although elements, alloys, oxides, and alloys with lithium may have higher capacities.

[0139] In one embodiment of this application, the first negative electrode active material is provided as 60 parts by weight or more, based on 100 parts by weight of the first negative electrode active material layer composition, for a negative electrode for a lithium secondary battery.

[0140] In another embodiment, the first negative electrode active material may be 60 parts by weight or more, preferably 70 parts by weight or more, and 99 parts by weight or less, preferably 98 parts by weight or less, and more preferably 97 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0141] The first negative electrode active material layer composition according to this application has lower capacity characteristics than the second negative electrode active material, but by using a first negative electrode active material within the aforementioned range that exhibits less particle cracking during charge-discharge cycle progression or pre-lithiation, it has the advantage of enhancing lifespan characteristics without reducing the capacity performance of the negative electrode.

[0142] In one embodiment of this application, the first negative electrode active material layer composition further comprises at least one selected from the group consisting of a first negative electrode conductive material and a first negative electrode binder, and the second negative electrode active material layer composition may further comprise at least one selected from the group consisting of a second negative electrode conductive material and a second negative electrode binder.

[0143] In one embodiment of this application, the first negative electrode active material layer provides a negative electrode for a lithium secondary battery comprising a second negative electrode active material layer composition including a first negative electrode active material; a first negative electrode conductive material; and a first negative electrode binder.

[0144] In this case, the first negative electrode conductive material can be described in the same way as the second negative electrode conductive material described above.

[0145] In one embodiment of this application, the first negative electrode conductive material may satisfy the requirement of 0.1 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0146] In another embodiment, the first negative electrode conductive material may be 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.5 parts by weight or more and 15 parts by weight or less, and more preferably 1 part by weight or more and 10 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0147] Furthermore, the provisions regarding the first negative electrode binder may be applied to the provisions regarding the second negative electrode binder described above.

[0148] In one embodiment of this application, the first negative electrode binder is 15 parts by weight or less, preferably 10 parts by weight or less, more preferably 5 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition, and may be 1 part by weight or more, or 1.5 parts by weight or more.

[0149] The first negative electrode active material layer according to this application uses a carbon-based active material as the main active material, and uses less silicon-based active material. This allows for a relatively lower binder content compared to the second negative electrode active material layer, thereby maximizing the content of the first negative electrode active material and thus maximizing the capacity characteristics. Furthermore, the second negative electrode active material layer contains a relatively large amount of binder, strongly suppressing the first negative electrode active material layer, and efficiently suppressing volume expansion even if silicon-based active material is included in the first negative electrode active material layer.

[0150] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the total thickness of the first negative electrode active material layer is 30 μm or more and 150 μm or less, and the total thickness of the second negative electrode active material layer is 1 μm or more and 20 μm or less.

[0151] In another embodiment, the total thickness of the first negative electrode active material layer is 30 μm or more and 150 μm or less, preferably 50 μm or more and 130 μm or less, and more preferably 90 μm or more and 120 μm or less.

[0152] In another embodiment, the total thickness of the second negative electrode active material layer may be 1 μm or more and 20 μm or less, preferably 2 μm or more and 15 μm or less, and more preferably 4 μm or more and 15 μm or less.

[0153] In one embodiment of this application, the total loading amount of the first negative electrode active material layer composition is 5 mg / cm³. 2 More than 20mg / cm 2 The following applies, and the total loading amount of the second negative electrode active material layer composition is 0.1 mg / cm³. 2 More than 5mg / cm 2 The following negative electrode for lithium secondary batteries is provided.

[0154] In yet another embodiment, the total loading amount of the first negative electrode active material layer composition is 5 mg / cm³. 2 More than 20mg / cm 2 Preferably 6 mg / cm³ 2 More than 15mg / cm 2 More preferably, 7 mg / cm³ 2 More than 13mg / cm 2 The following is also acceptable.

[0155] In yet another embodiment, the total loading amount of the second negative electrode active material layer composition is 0.1 mg / cm³. 2 More than 5mg / cm 2 Preferably 0.3 mg / cm³ 2 More than 3mg / cm 2 More preferably, 0.4 mg / cm³ 2More than 2mg / cm 2 The following is also acceptable.

[0156] In this case, the total thickness and total loading amount of the first and second negative electrode active material layers are calculated based on the case where they are formed on both sides of the negative electrode current collector layer. When they are formed on the end face of the negative electrode current collector layer, they can be evaluated using half the values ​​within the above range. However, some errors that are clearly not half the values ​​may be included, specifically, an error range of ±5 μm for thickness and ±1.5 mg / cm for loading amount. 2 It may include an error of a certain magnitude.

[0157] For example, the statement that the thickness of the first negative electrode active material layer is 30 μm means that the total thickness of the first negative electrode active material layer formed on both sides of the negative electrode current collector layer is 30 μm, and if it is formed on one side of the negative electrode current collector layer, it may satisfy 15 μm ± 5 μm.

[0158] The first negative electrode active material layer composition and the second negative electrode active material layer composition have the loading amount, which allows for adjustment of the ratio of active materials contained in the first negative electrode active material layer and the second negative electrode active material layer. In other words, the amount of first negative electrode active material contained in the first negative electrode active material layer can be adjusted to optimize the capacity characteristics, and the amount of second negative electrode active material contained in the second negative electrode active material layer can also be adjusted to enhance the lifespan characteristics without degrading the capacity characteristics.

[0159] The loading amount can mean the weight of the composition for forming the negative electrode active material layer, and specifically, the loading amount of the composition can have the same meaning as the loading amount of the slurry containing the composition.

[0160] In particular, one embodiment of this application provides a negative electrode for a lithium secondary battery that satisfies the following formula 1. [Formula 1] 0.1 ≤ [B / (A+B)] x 100 (%) ≤ 15

[0161] In the above formula 1, A is the total thickness of the first negative electrode active material layer, which is between 30 μm and 150 μm. B is the total thickness of the second negative electrode active material layer.

[0162] In one embodiment of this application, formula 1 may satisfy the range 0.1 ≤ [B / (A+B)] × 100 (%) ≤ 15, preferably 0.3 ≤ [B / (A+B)] × 100 (%) ≤ 14.5, and more preferably 1.5 ≤ [B / (A+B)] × 100 (%) ≤ 14.5.

[0163] The negative electrode for lithium secondary batteries according to this application has a double-layer structure corresponding to a specific composition, and further, by adjusting the thickness range to the range of formula 1 above, the probability of problems occurring due to lithium deposition is extremely low. In other words, in the negative electrode for lithium secondary batteries according to this application, since the second negative electrode active material layer is located at the uppermost end, lithium deposition by the graphite-based active material described above is formed between the first negative electrode active material layer and the second negative electrode active material layer, thereby suppressing the formation of lithium dendrites on the surface of the negative electrode, eliminating short-circuit problems, and because the silicon potential is high, lithium moves smoothly to the second negative electrode active material layer.

[0164] Thus, the negative electrode for lithium secondary batteries according to this application takes advantage of the rapid charging benefits of electrodes that use a high content of Si particles as a single layer active material, and solves the problems of surface degradation, uniformity during pre-lithiation, and life characteristics that are drawbacks of such electrodes. In this way, the first negative electrode active material layer and the second negative electrode active material layer are constructed as a double layer, and specific compositions and thicknesses are applied.

[0165] In one embodiment of this application, the thickness of the first negative electrode active material layer may be 80% or more and 95% or less, based on the total thickness of the first negative electrode active material layer and the second negative electrode active material layer being 100%.

[0166] In one embodiment of this application, the negative electrode for the lithium secondary battery may be a pre-lithified negative electrode.

[0167] In one embodiment of the present application, 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, wherein the second negative electrode active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and SiC, and the first negative electrode active material includes one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride. Based on 100 parts by weight of the first negative electrode active material, the silicon-based active material is included in an amount of 5 parts by weight or less, and a method for manufacturing a negative electrode for a lithium secondary battery that satisfies Formula 1 is provided.

[0168] In the method for manufacturing the negative electrode, the composition and content included in each step can apply the foregoing content.

[0169] In one embodiment of the present application, 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 is provided.

[0170] That is, the step is a step of forming an active material layer on the negative electrode current collector layer, and in the double layer structure, it can mean a step of forming an active material layer on the surface (lower layer part) that contacts the current collector layer.

[0171] In one embodiment of the present application, applying the first negative electrode active material layer composition includes a step of applying and drying a first negative electrode slurry including the first negative electrode active material layer composition and a negative electrode slurry solvent.

[0172] At this time, the solid content of the first negative electrode slurry may satisfy the range of 10% to 50%, preferably 2% to 45%. <统一格式,将

[0173] 改为

[0173] In one embodiment of this application, the step of forming the first negative electrode active material layer may include the step of mixing the first negative electrode slurry; and the step of coating one or both sides of the negative electrode current collector layer with the mixed first negative electrode slurry, wherein the coating may be performed using coating methods commonly used in the industry.

[0174] In one embodiment of this application, the present invention provides a step of forming a second negative electrode active material by applying a second negative electrode active material layer composition to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer.

[0175] In other words, the above step is the step of forming a second negative electrode active material layer on the first negative electrode active material layer, and can be said to be the step of forming the active material layer on the surface (upper layer) away from the current collector layer in the double layer structure.

[0176] In one embodiment of this application, applying the second negative electrode active material layer composition includes the step of applying and drying the second negative electrode slurry, which contains the second negative electrode active material layer composition and the negative electrode slurry solvent.

[0177] In this case, the solid content of the second negative electrode slurry may be in the range of 10% to 40%.

[0178] In one embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the step of forming the second negative electrode active material layer includes the steps of: mixing the second negative electrode slurry; and coating the mixed second negative electrode slurry with the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer.

[0179] The aforementioned coating may be applied using coating methods commonly used in this industry.

[0180] The step of forming the second negative electrode active material layer can be similarly described in the explanation of the step of forming the first negative electrode active material layer.

[0181] One embodiment of this application provides 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 step; or a wet-on-wet step;

[0182] In one embodiment of this application, the wet-on-dry step can mean a step of applying the first negative electrode active material layer composition, drying it completely, and then applying the second negative electrode active material layer composition on top of it, while the wet-on-wet step means a step of applying the first negative electrode active material layer composition, not drying it, and then applying the second negative electrode active material layer composition on top of it.

[0183] In particular, the wet-on-dry process involves applying the first negative electrode active material layer composition, allowing it to dry completely, and then applying the second negative electrode active material layer composition on top of it. Through this process, the first negative electrode active material layer and the second negative electrode active material layer can have a clear boundary. As a result, the compositions contained in the first and second negative electrode active material layers do not mix, and the material can be constructed as a double layer.

[0184] In one embodiment of this application, the negative electrode slurry solvent can be used without limitation as long as it can dissolve the first negative electrode active material layer composition and the second negative electrode active material layer composition, and specifically water or NMP can be used.

[0185] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, which includes a step of pre-lithiation of a negative electrode having a first negative electrode active material layer and a second negative electrode active material layer formed on the negative electrode current collector, wherein the step of pre-lithiation of the negative electrode includes a lithium electroplating step; a lithium metal transfer step; a lithium metal deposition step; or a stabilized lithium metal powder (SLMP) coating step.

[0186] The negative electrode for lithium secondary batteries described above includes a first negative electrode active material layer containing a carbon-based active material as the main active material for enhancing lifespan and capacity characteristics, and a second negative electrode active material layer containing the aforementioned silicon-based active material and having a specific thickness, thus retaining the advantages of rapid charging. Furthermore, because the first negative electrode active material has the above composition and is highly irreversible, particularly advantageous effects can be obtained even during the pre-lithiation process in which the negative electrode is pre-charged. Compared to simply applying only the first negative electrode active material layer or the second negative electrode active material layer, having first and second negative electrode active materials with the above-described double-layer composition allows for maximization of capacity characteristics along with rapid charging.

[0187] In one embodiment of this application, the porosity of the first and second negative electrode active material layers may be in the range of 10% to 60%.

[0188] In another embodiment, the porosity of the first and second negative electrode active material layers may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0189] The porosity of the porosity varies depending on the composition and content of the active material, conductive material, and binder contained in the first and second negative electrode active material layers, thereby ensuring that the electrical conductivity and resistance of the electrodes are within an appropriate range.

[0190] One embodiment of this application provides a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0191] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0192] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, which contains the positive electrode active material.

[0193] 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 with a surface treatment of carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0194] 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; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be Li metal.

[0195] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0196] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitations 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 or 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more can be used.

[0197] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0198] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. Generally, any membrane used as a separation membrane in secondary batteries is acceptable without particular limitations, but those with low resistance to electrolyte ion movement while exhibiting excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0199] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0200] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0201] As the non-aqueous organic solvent, for example, 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0202] 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 that effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be created, and this mixture is even more preferable.

[0203] The metal salt can be a lithium salt, which is a substance that dissolves easily in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2- 、(CF3)5PF - 、(CF3)6P - 、CF3SO3 - 、CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - 、CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - 、CF3(CF2)7SO3 - 、CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of can be used.

[0204] 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, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc.

[0205] 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. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems. [Examples]

[0206] The following are preferred embodiments to aid in understanding the present invention. These embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such variations and modifications fall within the scope of the appended claims.

[0207] <Examples> <Manufacturing of negative electrodes> Example 1: Manufacturing of the negative electrode Manufacturing of the first negative electrode active material layer A first negative electrode active material layer composition was prepared using SiO (average particle size (D50): 3.5 μm) as a silicon-based active material, artificial graphite, a first conductive material, a third conductive material, and CMC:SBR as a binder in a weight ratio of 4.779:90.794:0.982:0.018:1.127:2.3. The first negative electrode slurry was produced by adding these materials to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 45% by weight).

[0208] The first conductive material is carbon black C (specific surface area: 58 m²). 2 The third conductive material is a carbon nanotube (dimensions: / g, diameter: 37nm).

[0209] As a mixing method, the first conductive material, the third conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0210] As the negative electrode current collector, a copper current collector (thickness: 8 μm) is coated on both sides with the first negative electrode slurry at a rate of 9.312 mg / cm³. 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form the first negative electrode active material layer (thickness: 114 μm).

[0211] Manufacturing of the second negative electrode active material layer As a silicon-based active material, SiO (average particle size (D50): 5 μm), a second conductive material, a third conductive material, and polyacrylamide as a binder were used to prepare a second negative electrode active material layer composition at a weight ratio of 80:9.6:0.4:10. It was added to distilled water as a solvent for forming the negative electrode slurry to produce a second negative electrode slurry (solid content concentration: 25% by weight).

[0212] The second conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the third conductive material is carbon nanotubes.

[0213] As a mixing method, the second conductive material, the third conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homomixer, and then the active material was added, followed by dispersion at 2500 rpm for 30 minutes to prepare a slurry.

[0214] The second negative electrode slurry was coated on the first negative electrode active material layer at a loading amount of 0.464 mg / cm 2 , rolled (roll press), and dried in a vacuum oven at 130 °C for 10 hours to form a second negative electrode active material layer (thickness: 5.6 μm). At this time, Equation 1 satisfied the range of 4.59.

[0215] In Example 1, a negative electrode was manufactured in the same manner as in Example 1, except that the thickness in Table 1 below and the range of Equation 1 were satisfied. For reference, the evaluated examples and comparative examples had a first negative electrode active material layer and a second negative electrode active material layer formed on both sides of the negative electrode current collector layer. The thicknesses (loading amounts) of the first negative electrode active material layer and the second negative electrode active material layer mean the total thicknesses of the first negative electrode active material layer and the second negative electrode active material layer formed on both sides.

[0216]

Table 1

[0217] Comparative Example 4: Manufacturing of the negative electrode In the production of the first negative electrode active material layer of Example 1, the negative electrode was manufactured in the same manner as in Example 1, except that SiO (average particle size (D50): 3.5 μm) was used as the silicon-based active material, artificial graphite, a first conductive material, a third conductive material, and CMC:SBR as a binder in a weight ratio of 7:88.573:0.982:0.018:1.127:2.3 instead of 4.779:90.794:0.982:0.018:1.127:2.3.

[0218] Comparative Example 5: Manufacturing of the negative electrode Manufacturing of the first negative electrode active material layer A first negative electrode active material layer composition was prepared using artificial graphite, a first conductive material, a third conductive material, and CMC:SBR as a binder in a weight ratio of 95.5:0.98:0.02:1:2.5. The composition was added to distilled water as a solvent for negative electrode slurry formation to produce the first negative electrode slurry (solid content concentration 45% by weight).

[0219] The first conductive material is carbon black C (specific surface area: 58 m²). 2 The third conductive material is a carbon nanotube (dimensions: / g, diameter: 37nm).

[0220] As a mixing method, the first conductive material, the third conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0221] As the negative electrode current collector, a copper current collector (thickness: 8 μm) is coated with the first negative electrode slurry at a rate of 8.012 mg / cm³ on both sides. 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form the first negative electrode active material layer (thickness: 98.2 μm).

[0222] Manufacturing of the second negative electrode active material layer A second negative electrode active material layer composition was prepared using SiO (average particle size (D50): 5 μm) as the silicon-based active material, and polyacrylamide as the second conductive material, third conductive material, and binder in a weight ratio of 80:9.6:0.4:10. The second negative electrode slurry was produced by adding these to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 25% by weight).

[0223] The second conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 The material has a density of 3.5 μm ( / g) and an average particle size (D50), and the third conductive material is carbon nanotubes.

[0224] As a mixing method, the second conductive material, the third conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0225] The second negative electrode slurry is added to the first negative electrode active material layer at a rate of 0.908 mg / cm³. 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form the second negative electrode active material layer (thickness: 11.2 μm). During this process, Equation 1 satisfied the range of 10.54.

[0226] Comparative Examples 5-8 In Comparative Example 5, the negative electrode was manufactured in the same manner as in Comparative Example 5, except that the thickness in Table 2 and the range in Formula 1 were satisfied. For reference, the evaluated examples and comparative examples had a first negative electrode active material layer and a second negative electrode active material layer formed on both sides of the negative electrode current collector layer, and the thickness (loading amount) of the first negative electrode active material layer and the second negative electrode active material layer refers to the total thickness of the first negative electrode active material layer and the second negative electrode active material layer formed on both sides.

[0227] [Table 2]

[0228] Comparative Example 9: Manufacturing of the negative electrode An active material layer composition was prepared using silicon-based active material Si (average particle size (D50): 5 μm), a first conductive material, and polyacrylamide as a binder in a weight ratio of 70:20:10. A negative electrode slurry was prepared by adding this composition to distilled water as a solvent for negative electrode slurry formation (solid content concentration 25% by weight).

[0229] The first conductive material is carbon black C (specific surface area: 58 m²). 2 Uses ( / g, diameter: 37nm).

[0230] As a mixing method, the first conductive material, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, then the active material was added, and the mixture was dispersed again at 2500 rpm for 30 minutes to prepare a slurry.

[0231] As the negative electrode current collector, 85 mg / 25 cm of the negative electrode slurry was applied to both sides of a copper current collector (thickness: 8 μm). 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 25.78 μm).

[0232] Comparative Example 10: Manufacturing of the negative electrode In Comparative Example 9, the anode was manufactured in the same manner as in Comparative Example 9, except that the active material layer composition was prepared using Si (average particle size (D50): 5 μm), SiO (average particle size (D50): 3.5 μm), and polyacrylamide as the first conductive material and binder in a weight ratio of 52.5:17.5:20:10.

[0233] The first conductive material is carbon black C (specific surface area: 58 m²). 2 The second conductive material is plate-shaped graphite (specific surface area: 17m² / g, diameter: 37nm), and the second conductive material is plate-shaped graphite (specific surface area: 17m²). 2 The material has a density of 3.5 μm ( / g) and an average particle size (D50), and the third conductive material is carbon nanotubes.

[0234] Comparative Example 11: Manufacturing of the negative electrode In the above-mentioned Example 1, the anode was prepared in the same manner as in Example 1, except that the second anode active material layer composition was prepared using artificial graphite as the second anode slurry, a first conductive material, a third conductive material, and CMC:SBR as a binder in a weight ratio of 95.5:0.98:0.02:1:2.5, and SiO (average particle size (D50): 5 μm) as the silicon-based active material, and polyacrylamide as the second conductive material, third conductive material, and binder in a weight ratio of 80:9.6:0.4:10 for the first anode slurry.

[0235] <Manufacturing of secondary batteries> LiNi 0.6 Co 0.2 Mn 0.2 A cathode slurry was prepared by adding 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 in a weight ratio of 97.21:1.2:1.59 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0236] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is used, and the positive electrode slurry is applied to both sides at a rate of 439.1 mg / 25 cm². 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 105.5 μm) and produce the positive electrode (positive electrode thickness: 117.5 μm, porosity: 26%).

[0237] A polyethylene separation membrane was interposed between the positive electrode and the negative electrode of Example 1, and an electrolyte was injected to produce the secondary battery of Example 1.

[0238] The electrolyte in question was prepared by adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte to an organic solvent mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 30:70, and then adding LiPF6 as a lithium salt at a concentration of 1M.

[0239] Secondary batteries were fabricated in the same manner as described above, except that the negative electrodes of the above Examples and Comparative Examples were used.

[0240] Experimental Example 1: Evaluation of Monocell Lifespan The fabricated secondary batteries were evaluated for their lifespan using an electrochemical charge / discharge machine, and the capacity retention rate was evaluated. The secondary batteries were cycled 200 times under the conditions of charging (0.33C CC / CV charging to 4.2V and 0.05C cut-off) and discharging (0.33C CC discharging to 2.5V cut-off), and then the capacity retention rate was confirmed.

[0241] The capacity retention rate of the 200th cycle was evaluated according to the following formula. The results are shown in Table 3 below. Capacity retention rate (%) = {(Discharge capacity in the 200th cycle) / (Discharge capacity in the 1st cycle)} × 100

[0242]

Table 3

[0243] As can be confirmed from Table 3 above, it was confirmed that Examples 1 to 3 of the present invention are superior in lifespan performance compared to Comparative Examples 1 to 4 and 8 to 11. When using silicon-based substances that are affected by volume expansion and contraction during charge and discharge, the lifespan performance is somewhat inferior, and it was confirmed that the higher the proportion of graphite-based substances without volume expansion and contraction, the more consistently excellent the lifespan performance.

[0244] Comparative Examples 2 and 3 have the same composition of the first negative electrode active material layer and the second negative electrode active material layer as Example 1, but do not satisfy the thickness range of the first negative electrode active material layer. In the case of Comparative Example 3, although the thickness of the first negative electrode active material layer increases and capacity characteristics are ensured, the content of the silicon-based active material contained in the first negative electrode active material layer increases, and it was confirmed that the lifespan performance is inferior as in Comparative Example 4.

[0245] In Comparative Examples 1 and 8, it was confirmed that the proportion of silicon-based material in the upper layer was too high, resulting in poor lifetime performance. In Comparative Examples 9 and 10, where the active material capacity was even larger, it was confirmed that the lifetime performance was even worse. This is because silicon-based active material with a capacity 10 times that of graphite was evaluated in the same voltage range as graphite, resulting in a greater degree of expansion and contraction.

[0246] In Comparative Example 11, the upper and lower layers were inverted, and the volume expansion and contraction of the lower layer in contact with the foil caused electrode detachment, resulting in a decrease in performance.

[0247] For reference, Comparative Examples 5-7 did not contain silicon-based active material in the first negative electrode active material layer and showed a similar level of lifespan performance to the Examples. However, the rapid charging evaluation described later confirmed that their performance was significantly inferior due to the absence of silicon-based active material.

[0248] Experiment Example 2: Evaluation of Rapid Charging The secondary batteries manufactured as described above were subjected to rapid charging evaluation using an electrochemical charger / discharger, and the charging time for each was confirmed. The rapid charging evaluation involved performing three cycles at 0.33C / 0.33C, after which the third discharge capacity was defined as the cell's capacity. Then, in the fourth cycle, the battery was first charged at 0.33C, and then discharged to 80% of the third discharge capacity. That is, the battery was discharged at 0.33C until a voltage remained at 20% of the cell's capacity, and then charged to 80% at 4.5C. In conclusion, an evaluation was conducted to confirm the time required to charge the cell to 20-80% capacity, and the results are recorded in Table 4.

[0249] [Table 4]

[0250] Because silicon-based active materials have a higher capacitance than graphite-based active materials, a higher C-rate is applied to graphite-based active materials even when the same C-rate current is applied. Relatively speaking, silicon-based active materials are subjected to a lower C-rate, resulting in lower resistance, a longer CC (charge-conductivity) phase during charging, and a shorter charging time. Conversely, if the resistance is high, the voltage reaches 4.2V more quickly, a CV (voltage-conductivity) is applied, and the lower current results in a longer charging time.

[0251] In Table 4 above, Examples 1-3, which contain a specific amount of silicon-based active material in the lower layer, have relatively shorter charging times. In the case of Comparative Examples 5-7, which contain only graphite-based active material in the lower layer, while the lifespan performance is excellent, it was confirmed that the rapid charging performance is significantly inferior to that of Examples 1-3.

[0252] Comparative Examples 1 and 8 showed improved charging performance due to a higher proportion of the silicon-based upper layer. However, as can be seen in Table 3, the lifespan performance was significantly inferior. Comparative Examples 9 and 10, using pure Si with a large active material capacity, were suitable for rapid charging, but similarly, the lifespan performance was significantly reduced. Furthermore, Comparative Example 11, in which a graphite layer was formed in the upper layer, was found to be extremely poor for rapid charging. [Explanation of Symbols]

[0253] 10...Second negative electrode active material layer 20...first negative electrode active material layer 30 ···Negative electrode current collector layer

Claims

1. Negative electrode current collector layer; A first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and A second negative electrode active material layer provided on the side of the first negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer; A negative electrode for a lithium secondary battery, which includes, Contains carbon-based active material, The first negative electrode active material layer comprises a first negative electrode active material layer composition containing a first negative electrode active material, and the second negative electrode active material layer comprises a second negative electrode active material layer composition containing a second negative electrode active material. The second negative electrode active material layer comprises one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and SiC. The first negative electrode active material comprises a mixture of one or more materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides. The silicon-based active material is in an amount of 1 to 5 parts by weight, based on 100 parts by weight of the first negative electrode active material. The negative electrode for a lithium secondary battery that satisfies the following equation 1: [Formula 1] 0.1≦[B / (A+B)]x100(%)≦15 In the above formula 1, A is the total thickness of the first negative electrode active material layer, which is 30 μm or more and 150 μm or less. B is the total thickness of the second negative electrode active material layer.

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

3. The silicon-based active material comprises SiOx (0 < x < 2); or SiC, as described in claim 1, for a negative electrode for a lithium secondary battery.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein the second negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the second negative electrode active material layer composition.

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

6. The loading amount of the first negative electrode active material layer composition is 5 mg / cm². ２ 20mg / cm or more ２ The following: The loading amount of the second negative electrode active material layer composition is 0.1 mg / cm². ２ 5mg / cm or more ２ The negative electrode for a lithium secondary battery according to claim 1 is as follows:

7. The first negative electrode active material layer composition further comprises at least one selected from the group consisting of a first negative electrode conductive material and a first negative electrode binder. The anode for a lithium secondary battery according to claim 1, wherein the second anode active material layer composition further comprises at least one selected from the group consisting of a second anode conductive material and a second anode binder.

8. The carbon-based active material contains graphite, The aforementioned graphite includes artificial graphite and natural graphite. The negative electrode for a lithium secondary battery according to claim 1, wherein the weight ratio of the artificial graphite to the natural graphite is 5:5 to 9.5:0.

5.

9. The step of preparing the negative electrode current collector layer; A step of forming a first negative electrode active material layer by applying a first negative electrode active material layer composition containing the first negative electrode active material to one or both sides of the negative electrode current collector layer; and A step of forming a second negative electrode active material layer by applying a second negative electrode active material layer composition containing a second negative electrode active material to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer; A method for manufacturing a negative electrode for a lithium secondary battery, including, Contains carbon-based active material, The second negative electrode active material comprises one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and SiC. The first negative electrode active material comprises a mixture of one or more materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides. The silicon-based active material is in an amount of 1 to 5 parts by weight, based on 100 parts by weight of the first negative electrode active material. A method for manufacturing a negative electrode for a lithium secondary battery that satisfies the following formula 1: [Formula 1] 0.1≦[B / (A+B)]x100(%)≦15 In the above formula 1, A is the total thickness of the first negative electrode active material layer, which is 30 μm or more and 150 μm or less. B is the total thickness of the second negative electrode active material layer.

10. The process includes a step of pre-lithiation of the negative electrode, on which a first negative electrode active material layer and a second negative electrode active material layer are formed on the negative electrode current collector layer. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 9, wherein the step of pre-lithifying the negative electrode includes a lithium electroplating step; a lithium metal transfer step; a lithium metal deposition step; or a stabilized lithium metal powder (SLMP) coating step.

11. Positive electrode; A negative electrode for a lithium secondary battery according to any one of claims 1 to 8; A separation membrane provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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