KR20240010697A - Negative electrode for lithium secondary battery, method for preparing negative electrode for lithium secondary battery, and lithium secondary battery comprising negative electrode - Google Patents

Abstract

This application relates to a negative electrode for a lithium secondary battery, a method of manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

Description

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

This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0086772 filed with the Korea Intellectual Property Office on July 14, 2022, the entire contents of which are included in this specification.

This application relates to a negative electrode for a lithium secondary battery, a method of manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

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

Currently, secondary batteries are a representative example of electrochemical devices that use such electrochemical energy, and their use area is gradually expanding.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and are widely used. In addition, as an electrode for such a high-capacity lithium secondary battery, research is being actively conducted on methods for manufacturing a high-density electrode with a higher energy density per unit volume.

Generally, a secondary battery consists of an anode, a cathode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions from the positive electrode, and silicon-based particles with a large discharge capacity may be used as the negative electrode active material.

In particular, in response to the recent demand for high-density energy batteries, research is being actively conducted on ways to increase capacity by using silicon-based compounds such as Si/C or SiOx, which have a capacity more than 10 times greater than graphite-based materials, as anode active materials. there is. However, in the case of silicon-based compounds, which are high-capacity materials, compared to conventionally used graphite, they are high-capacity materials and have excellent capacity characteristics. However, during the charging process, the volume expands rapidly and the conductive path is cut off, deteriorating battery characteristics. , As a result, capacity drops from the beginning. In addition, silicon-based anodes are not uniformly charged with lithium ions in the depth direction of the anode when charging and discharging cycles are repeated, and the reaction progresses on the surface, accelerating surface deterioration, which requires performance improvement in terms of battery cycle.

Graphite electrodes exhibit excellent lifespan characteristics as silicon-based electrodes, but their fast charging performance is poor. Recently, as lithium secondary batteries have been used in various ways, research is being conducted to reduce the charging time for lithium secondary batteries, and charging of lithium secondary batteries needs to be completed within at least 20 minutes. Accordingly, in order to increase rapid charging performance, silicon-based cathodes with higher capacity and potential compared to graphite are used. However, silicon-based cathodes are experiencing the above-mentioned problems due to structural changes and collapse due to high capacity, and mixing silicon-based and graphite-based electrodes is occurring. In this case, the structure of the graphite electrode is also damaged and its lifespan characteristics are greatly reduced.

Accordingly, in order to solve the above problems when using a silicon-based compound with excellent rapid charging performance alone as a negative electrode active material, a method of controlling the driving potential, a method of additionally coating a thin film on the active material layer, and a method of controlling the particle size of the silicon-based compound are used. Various methods are being discussed, such as methods to suppress the volume expansion itself, such as the development of a binder to prevent the volume expansion of silicon-based compounds to prevent the conductive path from being disconnected.

However, in the case of the above methods, there are limits to their application because they can reduce battery performance, and there are still limits to the commercialization of negative battery manufacturing with a high content of silicon-based compounds with excellent fast charging performance, and the silicon-based active material layer contained in the silicon-based active material layer As the ratio of silicon-based active material increases, pre-lithiation is concentrated on the surface of the negative electrode, which causes damage to the silicon-based active material on the surface. As uneven pre-lithiation occurs, problems are occurring in improving lifespan characteristics.

Therefore, in order to improve the rapid charging performance of lithium secondary batteries, it is necessary to use silicon-based anodes, which are high-capacity materials, and to research lithium secondary batteries that can secure lifespan characteristics.

Japanese Patent Publication No. 2009-080971

In this application, while using a carbon-based active material in the negative electrode, a silicon-based buffer layer is formed by coating a silicon-based composition, which is a high-capacity material, in the range of Equation 1, which will be described later, so that the performance of rapid charging, which is an existing problem, can be secured, and furthermore, the capacity characteristics and Research has confirmed that cycle performance can be improved together. Accordingly, this application relates to a negative electrode for a lithium secondary battery, a method of manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

An exemplary embodiment of the present specification includes 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 a surface opposite to the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer, wherein the first negative electrode active material layer includes a first negative electrode active material. It includes a first negative electrode active material layer composition, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material, and the second negative electrode active material is SiOx (x = 0), SiOx ( 0<x<2) and SiC, and the first negative electrode active material is one selected from the group consisting of carbon-based active material, silicon-based active material, metal-based active material capable of alloying with lithium, and lithium-containing nitride. A negative electrode for a lithium secondary battery is provided, which includes at least 5 parts by weight of the silicon-based active material based on 100 parts by weight of the first negative active material, and satisfies the following equation 1.

[Equation 1]

0.1 ≤ [B / (A+B)]x100(%) ≤15

In equation 1 above,

A is the total thickness of the first negative 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.

In another embodiment, preparing a negative electrode current collector layer; forming a first negative electrode active material layer by applying a first negative electrode active material layer composition to one or both sides of the negative electrode current collector layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer, thereby forming a second negative electrode active material layer. A method of manufacturing a negative electrode for a lithium secondary battery comprising a. In this case, the second anode active material includes one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and SiC, and the first anode active material includes a carbon-based active material, a silicon-based active material, It contains at least one member selected from the group consisting of a metal-based active material capable of alloying with lithium and a lithium-containing nitride, and the silicon-based active material is included in an amount of 5 parts by weight or less based on 100 parts by weight of the first negative electrode active material, and satisfies Equation 1 above. A method for manufacturing a negative electrode for a lithium secondary battery is provided.

Finally, the anode; A negative electrode for a lithium secondary battery according to the present application; A separator provided between the anode and the cathode; It provides a lithium secondary battery including; and an electrolyte.

A negative electrode for a lithium secondary battery according to an exemplary 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 anode active material included in the second anode active material layer includes one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and SiC.

At this time, the second anode active material layer of the anode for a lithium secondary battery according to the present application satisfies the thickness in the range of Equation 1, and rapid charging performance can be maximized by thinly coating the second anode active material layer with high capacity characteristics. there is. Precipitation of lithium due to rapid charging, which is an existing problem, is caused by graphite-based active materials whose potential becomes negative due to high C-rate charging, and it has a feature that can solve this problem.

In addition, the first negative active material may include one or more selected from the group consisting of carbon-based active material, SiOx (0<x<2), SiC, and Si alloy, and in particular, carbon-based active material and SiOx (0<x<2). 2) may be included.

That is, since the negative electrode for a lithium secondary battery according to the present application has a second negative electrode active material layer at the uppermost part, lithium precipitation due to the above-described graphite-based active material is formed between the first negative electrode active material layer and the second negative electrode active material layer. The formation of lithium dendrites on the surface of the anode can be suppressed, so there is no short circuit problem, and since the silicon potential is high, it naturally moves to the second anode active material layer. In conclusion, the negative electrode for lithium secondary batteries according to the present application has a double layer structure according to a specific composition, and the thickness range is adjusted to the range of Equation 1, so the probability of problems due to lithium precipitation is greatly reduced. have it

In the end, the negative electrode for a lithium secondary battery according to the present application takes the advantage of rapid charging of an electrode using a high content of Si particles as a single-layer active material, but at the same time has the disadvantages of surface degradation, uniformity during pre-lithiation, and lifespan. In order to solve the problem of characteristics, the first negative electrode active material layer and the second negative electrode active material layer are composed of double layers, and a specific composition and thickness are applied.

Figure 1 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application.

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

In this specification, when a part “includes” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

In this specification, 'p to q' means a range of 'p to q or less.'

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

In this specification, “Dn” refers to particle size distribution and refers to the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. In other words, D50 is the particle size (average particle diameter) at 50% of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at 90% of the cumulative distribution of particle numbers according to particle size, and D10 is the cumulative particle number according to particle size. This is the particle size at 10% of the distribution. Meanwhile, particle size distribution can be measured using a 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 measuring device (for example, Microtrac S3500), and the difference in diffraction patterns according to particle size is measured when the particles pass through the laser beam, thereby distributing the particle size. Calculate .

In this specification, the fact that a polymer contains a certain monomer as a monomer unit means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when it is said that a polymer contains a monomer, this is interpreted the same as saying that the polymer contains a monomer as a monomer unit.

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

In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are determined by using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials, and using gel permeation chromatography (Gel Permeation). This is the polystyrene equivalent molecular weight measured by chromatography (GPC). In this specification, molecular weight means weight average molecular weight unless otherwise specified.

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

An exemplary embodiment of the present specification includes 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 a surface opposite to the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer, wherein the first negative electrode active material layer includes a first negative electrode active material. It includes a first negative electrode active material layer composition, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material, and the second negative electrode active material is SiOx (x = 0), SiOx ( 0<x<2) and SiC, and the first negative electrode active material is one selected from the group consisting of carbon-based active material, silicon-based active material, metal-based active material capable of alloying with lithium, and lithium-containing nitride. Provided is a negative electrode for a lithium secondary battery, which includes at least 5 parts by weight of the silicon-based active material based on 100 parts by weight of the first negative active material, and satisfies Equation 1.

In this application, in order to secure fast charging performance, which is a disadvantage of existing carbon-based negative electrodes, the upper layer of the carbon-based negative electrode is coated with a silicon-based active material layer having a range of formula 1, and the first negative electrode active material layer (lower layer) is the second negative electrode. It plays a role in preventing volume expansion of the active material layer (upper layer), and the second anode active material layer (upper layer) plays a role in securing rapid charging performance.

At this time, the first negative active material layer (lower layer) is mainly made of carbon-based active material, and in order to secure capacity characteristics, it is necessary to mix silicon-based active materials as in the present application to a degree that does not cause problems in life performance and to prevent volume expansion. It is important to use within the thickness range (A) that can be given. In addition, the second negative electrode active material layer (upper layer) must be coated with a thickness that satisfies a certain range (Equation 1) compared to the total negative electrode thickness to ensure both rapid charging and lifespan performance.

The negative electrode for a lithium secondary battery according to the present application has a double layer structure according to a specific composition and has a thickness range adjusted to the range of Equation 1, so that the probability of problems due to lithium precipitation is very low.

Figure 1 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery including a first negative electrode active material layer 20 and a second negative electrode active material layer 30 can be seen on one side of the negative electrode current collector layer 30, and Figure 1 shows the first negative electrode active material layer 30. Although the negative electrode active material layer is shown to be formed on one side, it may be included on both sides of the negative electrode current collector layer.

Hereinafter, the anode for a lithium secondary battery of the present invention will be described in more detail.

In an exemplary embodiment of the present application, 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 a surface opposite to the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer.

In an exemplary embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. This negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment of carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding power of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

In an exemplary 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.

However, the thickness may vary depending on the type and purpose of the cathode used and is not limited to this.

In an exemplary embodiment of the present application, the second anode active material may include one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and SiC.

In an exemplary embodiment of the present application, the second anode active material may be SiOx (0<x<2).

In an exemplary embodiment of the present application, the second anode active material may be SiC.

In an exemplary embodiment of the present application, the second anode active material includes at least one selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), based on 100 parts by weight of the second anode active material. The SiOx (x=0) may contain 95 parts by weight or more, preferably SiOx (x=0) may include 97 parts by weight or more, more preferably 99 parts by weight or more, and may contain 100 parts by weight or less. there is.

In an exemplary embodiment of the present application, the second anode active material may particularly use pure silicon (Si) particles. Using pure silicon (Si) as the first anode active material means that, based on 100 parts by weight of the first anode active material as described above, pure Si particles (SiOx (x=0)) that are not combined with other particles or elements ) may be included in the above range.

The second anode active material used in the second anode active material layer of the present invention involves a very complex crystal change in the reaction of electrochemically absorbing, storing, and releasing lithium atoms. As the reaction to electrochemically absorb, store, and release lithium atoms progresses, the composition and crystal structure of the silicon particles change to Si (crystal structure: Fd3m), LiSi (crystal structure: I41/a), and Li2Si (crystal structure: C2/m). ), Li7Si2(Pbam), Li22Si5(F23), etc. Additionally, due to changes in the complex crystal structure, the volume of silicon particles expands approximately four times. Therefore, when the charge and discharge cycle is repeated, the silicon particles are destroyed, and as the bond between the lithium atom and the silicon particle is formed, the insertion site of the lithium atom that the silicon particle initially had is damaged, which can significantly reduce the cycle life. .

In an exemplary embodiment of the present application, the second anode active material may be made of SiOx (x=0).

The second anode active material layer according to the present application includes a second anode active material, and specifically includes pure silicon particles containing 95 parts by weight or more of SiOx (x=0). At this time, when it contains a high content of pure silicon particles, the capacity characteristics may be excellent.

Meanwhile, the average particle diameter (D50) of the second anode active material of the present invention may be 3㎛ to 10㎛, specifically 4㎛ to 8㎛, and more specifically 5㎛ to 7㎛. When the average particle diameter is within the above range, the specific surface area of the particles is within an appropriate range, and the viscosity of the anode slurry is within an appropriate range. Accordingly, dispersion of the particles constituting the cathode slurry becomes smooth. In addition, since the size of the first negative active material is greater than the above lower limit, the contact area between the silicon particles and the conductive material is excellent due to the composite composed of the conductive material and the binder in the negative electrode slurry, so there is a possibility that the conductive network will be maintained. This increases the capacity maintenance rate. Meanwhile, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded to form a smooth surface of the cathode, thereby preventing current density unevenness during charging and discharging.

In one embodiment of the present application, the second anode active material generally has a 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. BET surface area is measured according to DIN 66131 (using nitrogen).

In one embodiment of the present application, the second anode active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragment-shaped particles. Alternatively but less preferably, the silicone particles may also have a fibrous structure or be present in the form of a silicone-comprising film or coating.

In an exemplary embodiment of the present application, the second negative active material may have a non-spherical shape and the 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. It is 0.9.

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

[Equation 1-1]

4πA'/P ²

In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided in which 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.

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

The second anode active material layer composition according to the present application can minimize surface deterioration by using the second anode active material layer in the thickness range described later even if the second anode active material with a significantly high capacity is used in the above range, and can also be used for rapid charging. It has very excellent performance characteristics.

In the past, it was common to use only graphite-based compounds as negative electrode active materials, but recently, as demand for high-capacity batteries increases, attempts to use silicon-based compounds mixed to increase capacity are increasing. However, in the case of silicon-based compounds, there is a limitation in that the volume rapidly expands during the charging/discharging process, damaging the conductive path formed in the negative electrode active material layer, thereby reducing battery performance.

Therefore, in an exemplary embodiment of the present application, the second anode active material layer composition includes a second anode conductive material; And it may further include one or more selected from the group consisting of a second negative electrode binder.

At this time, the second anode conductive material and the second anode binder included in the second anode active material layer composition may be those used in the art without limitation.

In an exemplary embodiment of the present application, the second anode conductive material may be any material commonly used in the art without limitation, and specifically, a point-type conductive material; Planar conductive material; And it may include one or more selected from the group consisting of linear conductive materials.

In an exemplary embodiment of the present application, the point-shaped conductive material refers to a conductive material that can be used to improve conductivity in the cathode, has conductivity without causing chemical change, and has a point-shaped or spherical shape. Specifically, the dot-shaped conductive material is natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, Parness black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, It may be at least one selected from the group consisting of potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of realizing high conductivity and excellent dispersibility.

In an exemplary embodiment of the present application, the point-shaped conductive material may have a BET specific surface area of 40 m ² /g or more and 70 m ² /g or less, preferably 45 m ² /g or more and 65 m ² /g or less, more preferably 50 m ^{2 /g.} It may be more than /g and less than 60m ² /g.

In an exemplary embodiment of the present application, the particle diameter of the point-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

In an exemplary embodiment of the present application, the second anode conductive material may include a planar conductive material.

The planar conductive material improves conductivity by increasing surface contact between silicon particles within the cathode, and at the same time can play a role in suppressing disconnection of the conductive path due to volume expansion. It is a plate-shaped conductive material or a bulk-type conductive material. It can be expressed as

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

In an exemplary embodiment of the present application, the average particle diameter (D50) of the planar conductive material may be 2㎛ to 7㎛, specifically 3㎛ to 6㎛, and more specifically 4㎛ to 5㎛. . When the above range is satisfied, dispersion is easy without causing an excessive increase in viscosity of the anode slurry due to the sufficient particle size. Therefore, the dispersion effect is excellent when dispersed using the same equipment and time.

In one embodiment of the present application, 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. It provides a negative electrode composition.

In an exemplary embodiment of the present application, the planar conductive material is a high specific surface area planar conductive material having a high BET specific surface area; Alternatively, a low specific surface area planar conductive material can be used.

In an exemplary embodiment of the present application, the planar conductive material includes a high specific surface area planar conductive material; Alternatively, a planar conductive material with a low specific surface area can be used without limitation, but in particular, the planar conductive material according to the present application can be affected to some extent by dispersion on electrode performance, so it is possible to use a planar conductive material with a low specific surface area that does not cause problems with dispersion. This may be particularly desirable.

In an exemplary embodiment of the present application, the planar conductive material may have a BET specific surface area of 5 m ² /g or more.

In another embodiment, the planar conductive material may have a BET specific surface area of 5 m ² /g or more and 500 m ² /g or less, preferably 5 m ² /g or more and 300 m ² /g or less, more preferably 5 m ^{2 /g} or more. It may be more than g and less than 250m ² /g.

In another embodiment, the planar conductive material is a high specific surface area planar conductive material, and has a BET specific surface area of 50 m ² /g or more and 500 m ² /g or less, preferably 80 m ² /g or more and 300 m ² /g or less, more preferably In other words, it can satisfy the range of 100m ² /g or more and 300m ² /g or less.

In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and has a BET specific surface area of 5 m ² /g or more and 40 m ² /g or less, preferably 5 m ² /g or more and 30 m ² /g or less, more preferably In other words, it can satisfy the range of 5m ² /g or more and 25m ² /g or less.

Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the 'bundle type' herein refers to a bundle in which a plurality of carbon nanotube units are arranged side by side or entangled in substantially the same orientation along the longitudinal axis of the carbon nanotube units, unless otherwise specified. It refers to a secondary shape in the form of a bundle or rope. The carbon nanotube unit has a graphite sheet in the shape of a cylinder with a nano-sized diameter and an sp2 bond structure. At this time, the characteristics of a conductor or semiconductor can be displayed depending on the angle and structure at which the graphite surface is rolled. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed when manufacturing a cathode, and can smoothly form a conductive network within the cathode, improving the conductivity of the cathode.

In particular, the linear conductive material according to an exemplary embodiment of the present application may be a single-walled carbon nanotube (SWCNT).

The single-walled carbon nanotube is a material in which carbon atoms arranged in a hexagon form a tube. It exhibits insulator, conductor, or semiconductor properties depending on its unique chirality, and the carbon atoms are connected by strong covalent bonds. Its tensile strength is approximately 100 times greater than that of steel, it has excellent flexibility and elasticity, and is chemically stable.

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. If the average diameter of the single-walled carbon nanotubes satisfies this range, the electrical conductivity of the cathode can be maintained even if the single-walled carbon nanotubes are included in a very small amount, and a desirable viscosity and solid content can be obtained when preparing a conductive material dispersion. This is possible. In the conductive material dispersion, single-walled carbon nanotubes may be aggregated together and exist in an entangled state (aggregate). Accordingly, the average diameter is determined by confirming the diameter of any entangled single-walled carbon nanotube aggregate extracted from the conductive material dispersion by SEM or TEM, and then measuring the diameter of the aggregate by measuring the diameter of the single-walled carbon nanotubes constituting the aggregate. It can be derived by dividing by the number of .

The BET specific surface area of the single-walled carbon nanotube may be 500 m ² /g to 1,500 m ² /g, or 900 m ² /g to 1,200 m ² /g, specifically 250 m ² /g to 330 m ² It can be /g. When the above range is satisfied, a conductive material dispersion with a desirable solid content is derived, and the viscosity of the negative electrode slurry is prevented from increasing excessively. The BET specific surface area can be measured through the nitrogen adsorption BET method.

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 to 100 ㎛, or 5 to 50 ㎛. When the aspect ratio or length satisfies this range, the specific surface area is at a high level, so the single-walled carbon nanotubes can be adsorbed to the active material particles with strong attraction within the cathode. Accordingly, the conductive network can be smoothly maintained even when the volume of the negative electrode active material expands. The aspect ratio can be confirmed by calculating the average of the aspect ratios of 15 single-walled carbon nanotubes with a large aspect ratio and 15 single-walled carbon nanotubes with a small aspect ratio when observing the single-walled carbon nanotube powder through an SEM.

Compared to multi-walled carbon nanotubes or double-walled carbon nanotubes, single-walled carbon nanotubes are advantageous in that they have a large aspect ratio, are long, and have a large volume, so an electrical network can be built using only a small amount.

In an exemplary embodiment of the present application, the second anode conductive material may satisfy an amount of 1 part by weight or more and 40 parts by weight or less based on 100 parts by weight of the second anode active material layer composition.

In another embodiment, the second anode conductive material is contained in an amount of 1 part by weight or more and 40 parts by weight or less, preferably 3 parts by weight or more and 30 parts by weight or less, more preferably, based on 100 parts by weight of the second anode active material layer composition. It may be 3 parts by weight or more and 15 parts by weight or less.

In an exemplary embodiment of the present application, the second anode conductive material is a point-shaped conductive material; Planar conductive material; and a linear conductive material, wherein the point-shaped conductive material: planar conductive material: linear conductive material may satisfy a ratio of 1:1:0.01 to 1:1:1.

In an exemplary embodiment of the present application, the point-shaped conductive material is present in an amount 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, more preferably 10 parts by weight, based on 100 parts by weight of the second anode conductive material. The range of more than 50 parts by weight and less than 50 parts by weight can be satisfied.

In an exemplary embodiment of the present application, the planar conductive material is present in an amount 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, more preferably 10 parts by weight, based on 100 parts by weight of the second anode conductive material. The range of more than 50 parts by weight and less than 50 parts by weight can be satisfied.

In an exemplary embodiment of the present application, the linear conductive material is 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, more preferably 0.1 parts by weight, based on 100 parts by weight of the second anode conductive material. The range of more than 5 parts by weight and less than 5 parts by weight can be satisfied.

In an exemplary embodiment of the present application, the second anode conductive material is a linear conductive material; And it may include a planar conductive material.

In an exemplary embodiment of the present application, the second anode 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.

In an exemplary embodiment of the present application, the second anode conductive material particularly includes a linear conductive material and a planar conductive material and satisfies the above composition and ratio, so it does not significantly affect the lifespan characteristics of the existing lithium secondary battery, As the number of possible charging and discharging points increases, it has excellent output characteristics at high C-rate.

The second negative conductive material according to the present application provides a negative electrode for a lithium secondary battery that includes at least a linear conductive material.

In an exemplary embodiment of the present application, the second anode conductive material may be made of a linear conductive material.

In this case, based on 100 parts by weight of the second negative active material, the linear conductive material may be 0.1 to 2 parts by weight, or 0.1 to 0.7 parts by weight, or 0.1 to 0.3 parts by weight. When the content of the linear conductive material satisfies this range, an electrical network can be sufficiently built within the negative electrode active material layer, and it is advantageous in terms of mixing and coating processability during electrode manufacturing. In addition, in the negative electrode according to one embodiment of the present invention, a linear conductive material is included in both the first negative electrode active material layer and the second negative electrode active material layer, so that a conductive network between active materials can be maintained according to volume expansion and contraction of the Si electrode, thereby improving service life. It is also advantageous, and rapid charging performance can be maintained. Basically, the Si-based cathode is advantageous in terms of fast-charging performance because it can be coated with a thin film compared to graphite, but the linear conductive material maintains the conductive network robustly, which is helpful for rapid charging and further improves the initial plunge in the lifespan of the Si-based cathode. and may be more helpful in maintaining lifespan.

In the case of the second anode conductive material according to the present application, it has a completely different configuration from the anode conductive material applied to the anode. That is, in the case of the second anode conductive material according to the present application, it serves to hold the contact point between silicon-based active materials whose volume expansion of the electrode is very large due to charging and discharging. The anode conductive material acts as a buffer when rolled. It plays a role in providing some conductivity, and its composition and role are completely different from the cathode conductive material of the present invention.

In addition, the second anode conductive material according to the present application is applied to a silicon-based active material and has a completely different configuration from the conductive material applied to the graphite-based active material. In other words, the conductive material used in the electrode having the graphite-based active material simply has smaller particles compared to the active material, so it has the property of improving output characteristics and providing some conductivity. As in the present invention, the first negative conductive material applied together with the silicon-based active material is The composition and role are completely different from those of

In an exemplary embodiment of the present application, the second negative binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, or polyacrylonitrile. ), polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid , ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and a group consisting of materials in which hydrogen thereof is replaced with Li, Na, or Ca, etc. It may include at least one selected from, and may also include various copolymers thereof.

The second anode binder according to an exemplary embodiment of the present application serves to hold the active material and the conductive material to prevent distortion and structural deformation of the anode structure in the volume expansion and relaxation of the second anode active material. If satisfies, all general binders can be applied, specifically a water-based binder can be used, and more specifically, a PAM-based binder can be used.

In an exemplary embodiment of the present application, the amount of 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, 1 It may be more than 5 parts by weight or more.

Compared to the first anode active material layer described later, the content of the above-described second anode binder is contained at a high level, so that it can strongly hold the first anode active material layer, thereby reducing the volume expansion of the silicon-based active material included in the first anode active material layer. It may have a deterrent effect.

In an exemplary 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 the first negative electrode active material Based on 100 parts by weight, the silicon-based active material contains 5 parts by weight or less.

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

The first negative active material layer (lower layer) is mainly made of carbon-based active material, and in order to secure capacity characteristics, it is necessary to mix silicon-based active materials as in the present application to a degree that does not cause problems in life performance, and can prevent volume expansion. It is important to use within the available thickness range (A).

In an exemplary embodiment of the present application, the first anode active material is a carbon-based active material; And it may include a silicon-based active material mixed composition.

In an exemplary embodiment of the present application, the silicon-based active material included in the first anode active material may include one or more selected from the group consisting of SiOx (0<x<2), SiC, and Si alloy.

In an exemplary embodiment of the present application, the silicon-based active material is SiOx (0<x<2); Alternatively, a negative electrode for a lithium secondary battery containing SiC is provided.

In another embodiment, the silicon-based active material included in the first anode active material may include SiOx (0<x<2).

In another embodiment, the silicon-based active material included in the first anode active material may include SiC.

The negative electrode for a lithium secondary battery according to the present application is composed of a double layer and includes the first negative electrode active material in the first negative electrode active material layer as described above. Specifically, a carbon-based active material is used as the main active material, and a silicon-based active material is used. When used with or without use, the overall lifespan characteristics of the electrode are enhanced, and the problem of rapid charging accordingly is solved by including the second anode active material layer described above.

In an exemplary embodiment of the present application, representative examples of the carbon-based active material include natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, or activated carbon, Any carbon material commonly used in lithium secondary batteries can be used without limitation, and can be specifically processed into a spherical or dot-shaped form.

In an exemplary embodiment of the present application, the carbon-based active material includes graphite, the graphite includes artificial graphite and natural graphite, and the weight ratio of the artificial graphite and natural graphite is 5:5 to 9.5:0.5. A negative electrode for a lithium secondary battery is provided.

Artificial graphite according to an embodiment of the present invention may be in the form of primary particles or may be in the form of secondary particles in which a plurality of the primary particles are aggregated.

The term "initial particle" used in the present invention refers to the original particle when another type of particle is formed from a certain particle, and a plurality of primary particles are aggregated, combined, or assembled to form secondary particles. can be formed.

The term “secondary particles” used in the present invention refers to large, physically distinguishable particles formed by aggregating, combining, or assembling individual primary particles.

The artificial graphite of the primary particles may be manufactured by heat treating one or more types selected from the group consisting of needle cokes, mosaic cokes, and coal tar pitch.

The artificial graphite is generally manufactured by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum heavy oils at over 2,500°C, and after graphitization, the particle size is adjusted such as grinding and secondary particle formation. It can be used as a negative electrode active material. In the case of artificial graphite, crystals are randomly distributed within the particles, and have a lower degree of sphericity and a somewhat sharp shape compared to natural graphite.

Artificial graphite used in one embodiment of the present invention includes commercially used mesophase carbon microbeads (MCMB), mesophase pitch-based carbon fiber (MPCF), artificial graphite graphitized in the form of a block, and artificial graphite graphitized in the form of a powder. There may be graphite, etc. The sphericity of the artificial graphite may be 0.91 or less, or 0.6 to 0.91, or 0.7 to 0.9.

Additionally, the artificial graphite may have a particle size of 5 to 30 μm, preferably 10 to 25 μm.

Specifically, the D50 of the artificial graphite primary particles may be 6㎛ to 15㎛, 6㎛ to 10㎛, and 6㎛ to 9㎛. When the D50 of the primary particles satisfies this range, the primary particles can be formed to have high graphitization, and the orientation index of the negative electrode active material particles can be appropriately secured, thereby improving rapid charging performance.

The artificial graphite secondary particles may be formed by granulating primary particles. That is, the secondary particles may be a structure formed by agglomerating the primary particles through an assembly process. The secondary particles may include a carbonaceous matrix that allows the primary particles to aggregate. The carbonaceous matrix may include at least one of soft carbon and graphite. The soft carbon may be formed by heat treating the pitch.

The carbonaceous matrix may be included in the secondary particles in an amount of 8% by weight to 16% by weight, and specifically may be included in an amount of 9% by weight to 12% by weight. The above range is lower than the content of carbonaceous matrix used in conventional artificial graphite secondary particles. This means that the particle size of the primary particles within the secondary particles is controlled, so that structurally stable secondary particles can be manufactured even if the content of the carbonaceous matrix required for granulation is small, and the amount of primary particles constituting the secondary particles is also low. It can be uniform.

A carbon coating layer may be included on the surface of the artificial graphite secondary particles, and the carbon coating layer may include at least one of amorphous carbon and crystalline carbon.

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 fluorene and graphene.

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

The carbide of other organic substances may be a carbide of an organic substance selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or cedohexose, and combinations thereof.

The D50 of the artificial graphite secondary particles may be 10㎛ to 25㎛, specifically 12㎛ to 22㎛, and more specifically 13㎛ to 20㎛. When the above range is satisfied, the artificial graphite secondary particles can be evenly dispersed within the slurry and the charging performance of the battery can also be improved.

The tap density of the artificial graphite secondary particles may be 0.85 g/cc to 1.30 g/cc, specifically 0.90 g/cc to 1.10 g/cc, and more specifically 0.90 g/cc to 1.07 g/cc. It can be. When the above range is satisfied, it means that the packing of the artificial graphite secondary particles can be performed smoothly within the cathode, and thus the cathode adhesion can be improved.

The natural graphite may generally be a plate-shaped aggregate before being processed, and the plate-shaped particles are spherical with a smooth surface through post-processing such as particle grinding and reassembly processes in order to be used as an active material for electrode production. It can be manufactured in any form.

Natural graphite used in one embodiment of the present invention may have a sphericity of greater than 0.91 and less than or equal to 0.97, or 0.93 to 0.97, or 0.94 to 0.96.

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

According to one embodiment of the present invention, the weight ratio of the artificial graphite and natural graphite is 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 the artificial graphite and natural graphite satisfies this range, better output can be achieved and can be advantageous in terms of lifespan and rapid charging performance.

In an exemplary embodiment of the present application, the planar conductive material used as the above-described negative electrode conductive material has a different structure and role from the carbon-based active material generally used as the negative electrode active material. Specifically, the carbon-based active material used as a negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot-shaped shape to facilitate storage and release of lithium ions.

On the other hand, the planar conductive material used as a negative electrode conductive material is a material that has a plane or plate shape and can be expressed as plate-shaped graphite. In other words, it is a material included to maintain a conductive path within the negative electrode active material layer, and refers to a material that does not play a role in storing and releasing lithium, but rather secures a conductive path in a planar shape inside the negative electrode active material layer.

That is, in the present application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-shaped shape and used as a material that secures a conductive path rather than storing or releasing lithium. At this time, the negative electrode active material included has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

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

That is, in an exemplary embodiment of the present application, artificial graphite or natural graphite, which is a carbon-based active material, may satisfy a BET specific surface area of 0.1 m ² /g or more and 4.5 m ² /g or less. In addition, plate-shaped graphite, which is a planar conductive material, is in the form of a planar surface and may have a BET specific surface area of 5 m ² /g or more.

Representative examples of the metal-based active material include Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, Sb, Ga, Mn, Fe, Co, Ni, Cu, Sr and Ba. It may be a compound containing one or two or more metal elements selected from the group consisting of. These metal compounds can be used in any form, such as simple substance, alloy, oxide (TiO ₂ , SnO _2, etc.), nitride, sulfide, boride, and alloy with lithium, but simple substance, alloy, oxide, and alloy with lithium have high capacity. It can be.

In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided in which the first negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the first negative electrode active material layer composition.

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, based on 100 parts by weight of the first negative electrode active material layer composition. parts or less, more preferably 97 parts by weight or less.

The first anode active material layer composition according to the present application has lower capacity characteristics than the second anode active material, but the capacity performance of the anode can be improved by using the first anode active material, which is less prone to particle breakage during charge/discharge cycle or pre-lithiation, within the above range. It does not deteriorate and has the characteristic of enhancing lifespan characteristics.

In an exemplary embodiment of the present application, the first negative electrode active material layer composition includes a first negative electrode conductive material; and a first negative electrode binder, wherein the second negative electrode active material layer composition includes a second negative electrode conductive material; And it may further include one or more selected from the group consisting of a second negative electrode binder.

In an exemplary embodiment of the present application, the first negative electrode active material layer includes a first negative electrode active material; A first cathode conductive material; and a second negative electrode active material layer composition including a first negative electrode binder.

At this time, the description of the above-described second cathode conductive material may be applied to the first cathode conductive material.

In an exemplary embodiment of the present application, the first anode conductive material may satisfy an amount of 0.1 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the first anode active material layer composition.

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

Additionally, the content regarding the first cathode binder may be applied to the above-described second cathode binder.

In an exemplary embodiment of the present application, the amount of 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, 1 It may be more than 1.5 parts by weight or more.

The first negative electrode active material layer according to the present application uses carbon-based active material as the main active material, and the use of silicon-based active material is small, so the binder content can be used in a relatively smaller amount compared to the second negative electrode active material layer, and accordingly, the first negative electrode active material It has the characteristic of maximizing capacity characteristics by maximizing the content. In addition, a relatively large amount of binder is included in the second anode active material layer to strongly hold the first anode active material layer, so that volume expansion can be efficiently suppressed even if the first anode active material layer contains a silicon-based active material.

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

In another embodiment, the total thickness of the first negative active material layer may be 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.

In another embodiment, the total thickness of the second negative 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.

In an exemplary embodiment of the present application, the total loading amount of the first negative electrode active material layer composition is 5 mg/cm ² or more and 20 mg/cm ² or less, and the total loading amount of the second negative electrode active material layer composition is 0.1 mg/cm ² or more and 5 mg. A negative electrode for a lithium secondary battery having a thickness of /cm ² or less is provided.

In another embodiment, the total loading amount of the first negative active material layer composition is 5 mg/cm ² or more and 20 mg/cm ² or less, preferably 6 mg/cm ² or more and 15 mg/cm ² or less, more preferably 7 mg/cm 2 It may be ² or more and 13 mg/cm ² or less.

In another embodiment, the total loading amount of the second negative active material layer composition is 0.1 mg/cm ² or more and 5 mg/cm ² or less, preferably 0.3 mg/cm ² or more and 3 mg/cm ^{2 or less, more preferably 0.4 mg/cm 2} or more. It may be mg/cm ² or more and 2 mg/cm ² or less.

At this time, the total thickness and total loading amount of the first and second negative electrode active material layers are calculated based on when they are formed on both sides of the negative electrode current collector layer, and when formed on the cross section of the negative electrode current collector layer, they are half of the above range. It can be evaluated as a value of . However, it may include some errors rather than clearly half the value, and specifically, in the case of thickness, it may include an error range of ±5 μm, and in the case of loading amount, it may include an error of ±1.5 mg/cm ² .

For example, the thickness of the first negative electrode active material layer is 30 μm, meaning 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 when formed on the cross section of the negative electrode current collector layer. 15μm±5μm can be satisfied.

When the first negative electrode active material layer composition and the second negative electrode active material layer composition have the above loading amounts, the ratio of active materials included in the first negative electrode active material layer and the second negative electrode active material layer can be adjusted. That is, the capacity characteristics can be optimized by adjusting the amount of the first negative electrode active material included in the first negative electrode active material layer, and at the same time, the capacity characteristics can be optimized by adjusting the amount of the second negative electrode active material included in the second negative electrode active material layer. It does not deteriorate and has the feature of enhancing lifespan characteristics.

The loading amount may mean the weight of the composition for forming the negative electrode active material layer. Specifically, the loading amount of the composition may have the same meaning as the loading amount of the slurry containing the composition.

In particular, in one embodiment of the present application, a negative electrode for a lithium secondary battery that satisfies the following equation 1 is provided.

[Equation 1]

0.1 ≤ [B / (A+B)]x100(%) ≤15

In equation 1 above,

A is the total thickness of the first negative 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.

In an exemplary embodiment of the present application, Equation 1 is 0.1 ≤ [B / (A+B)]x100(%) ≤15, preferably 0.3 ≤ [B / (A+B)]x100(%) ≤ 14.5, more preferably 1.5 ≤ [B / (A+B)]x100(%) ≤ 14.5.

The negative electrode for a lithium secondary battery according to the present application has a double layer structure according to a specific composition and has a thickness range adjusted to the range of Equation 1 above, so that the probability of problems due to lithium precipitation is very low. That is, since the negative electrode for a lithium secondary battery according to the present application has a second negative electrode active material layer at the uppermost part, lithium precipitation due to the above-described graphite-based active material is formed between the first negative electrode active material layer and the second negative electrode active material layer. The formation of lithium dendrites on the surface of the anode can be suppressed, so there is no short circuit problem, and since the silicon potential is high, it naturally moves to the second anode active material layer.

In the end, the negative electrode for a lithium secondary battery according to the present application takes the advantage of rapid charging of an electrode using a high content of Si particles as a single-layer active material, but at the same time has the disadvantages of surface degradation, uniformity during pre-lithiation, and lifespan. In order to solve the problem of characteristics, the first negative electrode active material layer and the second negative electrode active material layer are composed of double layers, and a specific composition and thickness are applied.

In an exemplary embodiment of the present application, the thickness of the first negative electrode active material layer may satisfy 80% or more and 95% or less based on 100% of the total combined thickness of the first negative electrode active material layer and the second negative electrode active material layer.

In an exemplary embodiment of the present application, the negative electrode for a lithium secondary battery may be a pre-lithiated negative electrode.

In one embodiment of the present application, preparing a negative electrode current collector layer; forming a first negative electrode active material layer by applying a first negative electrode active material layer composition to one or both sides of the negative electrode current collector layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer, thereby forming a second negative electrode active material layer. A method of manufacturing a negative electrode for a lithium secondary battery comprising a. In this case, the second anode active material includes one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and SiC, and the first anode active material includes a carbon-based active material, a silicon-based active material, It contains at least one member selected from the group consisting of a metal-based active material capable of alloying with lithium and a lithium-containing nitride, and the silicon-based active material is included in an amount of 5 parts by weight or less based on 100 parts by weight of the first negative electrode active material, and satisfies Equation 1 above. A method for manufacturing a negative electrode for a lithium secondary battery is provided.

In the method for manufacturing the anode, the composition and content included in each step may be as described above.

In an exemplary embodiment of the present application, a step of forming a first negative electrode active material layer is provided by applying a first negative electrode active material layer composition to one or both sides of the negative electrode current collector layer.

In other words, the above step is a step of forming an active material layer on the negative electrode current collector layer, and may mean forming the active material layer on the surface (lower layer) in contact with the current collector layer in a double layer structure.

In an exemplary embodiment of the present application, applying the first negative electrode active material layer composition includes: the first negative electrode active material layer composition; and applying and drying a first cathode slurry containing a cathode slurry solvent.

At this time, the solid content of the first cathode slurry may satisfy the range of 10% to 50%, preferably 2% to 45%.

In an exemplary embodiment of the present application, forming the first negative electrode active material layer includes mixing the first negative electrode slurry; And it may include the step of coating the mixed first negative electrode slurry on one or both sides of the negative electrode current collector layer, and the coating may be performed using a coating method commonly used in the art.

In an exemplary embodiment of the present application, a step of forming a second negative electrode active material is provided by applying a second negative electrode active material layer composition to the opposite side of the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer.

In other words, the step of forming a second negative electrode active material layer on the first negative electrode active material layer means forming the active material layer on the side (upper layer) away from the current collector layer in a double layer structure. You can.

In an exemplary embodiment of the present application, applying the second negative electrode active material layer composition includes: the second negative electrode active material layer composition; and applying and drying a second cathode slurry containing a cathode slurry solvent.

At this time, the solid content of the second cathode slurry may satisfy the range of 10% to 40%.

In an exemplary embodiment of the present application, forming the second anode active material layer includes mixing the second anode slurry; and coating the mixed second negative electrode slurry on the opposite side of the first negative electrode active material layer that is in contact with the negative electrode current collector layer.

The coating may be a coating method commonly used in the art.

The step of forming the second negative electrode active material layer may be identically applied to the step of forming the first negative electrode active material layer.

In an exemplary embodiment of the present application, forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet on dry process; Or a wet on wet process; provided is a manufacturing method of a negative electrode for a lithium secondary battery.

In an exemplary embodiment of the present application, the wet on dry process may refer to a process of applying the first negative electrode active material layer composition, drying it completely, and applying the second negative electrode active material layer composition on top, The wet on wet process refers to a process of applying the second negative electrode active material layer composition on top of the first negative electrode active material layer composition without drying it.

In particular, the wet on dry process involves 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. Through the above process, The first negative electrode active material layer and the second negative electrode active material layer may have a clear boundary. Accordingly, the compositions contained in the first negative electrode active material layer and the second negative electrode active material layer do not mix and have the characteristic of being composed of a double layer.

In an exemplary embodiment of the present 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. Specifically, water or NMP can be used.

In an exemplary embodiment of the present application, the method includes pre-lithiating 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, and pre-lithiating the negative electrode. The step is a lithium electrolytic plating process; Lithium metal transfer process; Lithium metal deposition process; Alternatively, a method for manufacturing a negative electrode for a lithium secondary battery comprising a stabilized lithium metal powder (SLMP) coating process is provided.

The negative electrode for a lithium secondary battery as described above contains a carbon-based active material as the main active material for enhancing lifespan and capacity characteristics as a first negative electrode active material layer, and is provided with the aforementioned silicon-based active material and a specific thickness as a second negative electrode active material layer, allowing rapid charging. You can take the advantages as is. Moreover, since the first negative electrode active material has the above composition and has high irreversibility, a particularly advantageous effect can be seen even during the pre-lithiation process of pre-charging the negative electrode. Compared to the case where only the first or second negative electrode active material layer is applied, the first and second negative electrode active materials having the above-described double layer composition can maximize capacity characteristics along with rapid charging.

In an exemplary embodiment of the present application, the porosity of the first and second negative electrode active material layers may satisfy a range of 10% to 60%.

In another embodiment, the porosity of the first and second negative active material layers is in the range of 10% to 60%, preferably 20% to 50%, more preferably 30% to 45%. You can be satisfied.

The porosity includes the active material included in the first and second negative active material layers; conductive material; And it varies depending on the composition and content of the binder, and accordingly, the electrical conductivity and resistance of the electrode are characterized by having an appropriate range.

In an exemplary embodiment of the present application, an anode; A negative electrode for a lithium secondary battery according to the present application; A separator provided between the anode and the cathode; It provides a lithium secondary battery including; and an electrolyte.

The secondary battery according to an exemplary embodiment of the present specification may particularly include the above-described negative electrode for a lithium secondary battery. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, detailed description will be omitted.

The positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and may include a positive electrode active material layer containing the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , surface treated with nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500㎛, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium iron oxide such as LiFe ₃ O ₄ ; Lithium manganese oxide with the formula Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _{2 ,} etc.; lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Chemical formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3). Ni site-type lithium nickel oxide; Chemical formula LiMn _2-c3 M _c3 O ₂ (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO lithium manganese composite oxide represented by ₈ (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); Examples include LiMn ₂ O ₄ in which part of Li in the chemical formula is replaced with an alkaline earth metal ion, but it is not limited to these. The anode may be Li-metal.

The positive electrode active material layer may include the positive electrode active material described above, a positive conductive material, and a positive electrode binder.

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

Additionally, the positive electrode binder serves to improve adhesion between positive electrode active material particles and 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, and carboxymethyl cellulose (CMC). ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber. (SBR), fluorine rubber, or various copolymers thereof, and one type of these may be used alone or a mixture of two or more types may be used.

The separator separates the cathode from the anode and provides a passage for lithium ions to move. It can be used without any particular restrictions as long as it is normally used as a separator in secondary batteries. In particular, it has low resistance to ion movement in the electrolyte and has excellent electrolyte moisturizing ability. It is desirable. Specifically, porous polymer films, for example, porous polymer films made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these. A laminated structure of two or more layers may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. In addition, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

The 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.

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

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dimethyl. Toxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxoran, formamide, dimethylformamide, dioxoran, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid. Triesters, trimethoxy methane, dioxoran derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl pyropionate, propionic acid. Aprotic organic solvents such as ethyl may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can be preferably used because they easily dissociate lithium salts. These cyclic carbonates include dimethyl carbonate and diethyl carbonate. If the same low-viscosity, low-dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte with high electrical conductivity can be made and can be used more preferably.

The metal salt may be a lithium salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte solution. For example, anions of the lithium salt include F ^- , Cl ^- , I ^- , NO ₃ ^- , N(CN) ) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- At least one selected from the group consisting of can be used.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trifluoroethylene for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexanoic acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida. One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride may be further included.

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 battery pack include the secondary battery with high capacity, high rate characteristics, and cycle characteristics, they are medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. It can be used as a power source.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the above examples are merely illustrative of the present description, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, It is natural that such variations and modifications fall within the scope of the attached patent claims.

<Example>

<Manufacture of cathode>

Example 1: Preparation of cathode

Manufacturing the first negative active material layer

SiO (average particle diameter (D50): 3.5㎛) as a silicon-based active material, artificial graphite, first conductive material, third conductive material, and CMC:SBR as a binder were prepared at a weight ratio of 4.779:90.794:0.982:0.018:1.127:2.3. 1 A negative electrode active material layer composition was prepared. A first negative electrode slurry was prepared by adding distilled water as a solvent for forming the negative electrode slurry (solids concentration: 45% by weight).

The first conductive material is carbon black C (specific surface area: 58 m ² /g, diameter: 37 nm), and the third conductive material is carbon nanotubes.

As a mixing method, the first and third conductive materials, binder, and water were dispersed at 2500 rpm for 30 min using a homo mixer, then the active material was added and dispersed at 2500 rpm for 30 min to prepare a slurry.

The first negative electrode slurry was coated at a loading amount of 9.312 mg/cm ² on both sides of a copper current collector (thickness: 8㎛) as a negative electrode current collector, rolled, and placed in a vacuum oven at 130°C for 10 hours. It was dried to form a first negative electrode active material layer (thickness: 114㎛).

Manufacturing the second negative active material layer

A second negative active material layer composition was prepared using SiO (average particle diameter (D50): 5㎛) as a silicon-based active material, a second conductive material, a third conductive material, and polyacrylamide as a binder at a weight ratio of 80:9.6:0.4:10. . A second negative electrode slurry was prepared by adding distilled water as a solvent for forming the negative electrode slurry (solids concentration: 25% by weight).

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

As a mixing method, the second and third conductive materials, binder, and water were dispersed at 2500 rpm for 30 min using a homo mixer, then the active material was added and dispersed at 2500 rpm for 30 min to prepare a slurry.

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

In Example 1, a negative electrode was manufactured in the same manner as 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 were those in which the first negative electrode active material layer and the second negative electrode active material layer were 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 thickness of the entire first negative electrode active material layer and the second negative electrode active material layer formed on both sides.

First cathode active material layer Second cathode active material layer Equation 1 Thickness (㎛) Loading amount (mg/cm ² ) Thickness (㎛) Loading amount (mg/cm ² ) Example 1 114 9.312 5.6 0.464 4.9 Example 2 99.5 8.128 11.1 0.904 11.2 Example 3 39.4 7.632 13.3 1.092 14.2 Comparative Example 1 77.5 6.332 19.4 1.584 25.0 Comparative Example 2 25 6.211 2 0.233 7.4 Comparative Example 3 155 10.512 18 1.562 10.4

Comparative Example 4: Preparation of cathode

In manufacturing the first negative active material layer of Example 1, SiO (average particle diameter (D50): 3.5 ㎛) as a silicon-based active material, artificial graphite, a first conductive material, a third conductive material, and CMC:SBR as a binder were used at a ratio of 4.779. A cathode was manufactured in the same manner as in the above example, except that the weight ratio of 7:88.573:0.982:0.018:1.127:2.3 was used instead of the weight ratio of :90.794:0.982:0.018:1.127:2.3.

Comparative Example 5: Preparation of cathode

Manufacturing the first negative active material layer

A first negative active material layer composition was prepared using artificial graphite, a first conductive material, a third conductive material, and CMC:SBR as a binder at a weight ratio of 95.5:0.98:0.02:1:2.5. A first negative electrode slurry was prepared by adding distilled water as a solvent for forming the negative electrode slurry (solids concentration: 45% by weight).

The first conductive material is carbon black C (specific surface area: 58 m ² /g, diameter: 37 nm), and the third conductive material is carbon nanotubes.

As a mixing method, the first and third conductive materials, binder, and water were dispersed at 2500 rpm for 30 min using a homo mixer, then the active material was added and dispersed at 2500 rpm for 30 min to prepare a slurry.

The first negative electrode slurry was coated at a loading amount of 8.012 mg/cm ² on both sides of a copper current collector (thickness: 8㎛) as a negative electrode current collector, rolled, and placed in a vacuum oven at 130°C for 10 hours. It was dried to form a first negative electrode active material layer (thickness: 98.2㎛).

Manufacturing the second negative active material layer

A second negative active material layer composition was prepared using SiO (average particle diameter (D50): 5㎛) as a silicon-based active material, a second conductive material, a third conductive material, and polyacrylamide as a binder at a weight ratio of 80:9.6:0.4:10. . A second negative electrode slurry was prepared by adding distilled water as a solvent for forming the negative electrode slurry (solids concentration: 25% by weight).

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

As a mixing method, the second and third conductive materials, binder, and water were dispersed at 2500 rpm for 30 min using a homo mixer, then the active material was added and dispersed at 2500 rpm for 30 min to prepare a slurry.

The second anode slurry was coated on the first anode active material layer at a loading amount of 0.908 mg/cm ² , rolled, and dried in a vacuum oven at 130° C. for 10 hours to form a second anode active material layer (thickness : 11.2㎛) was formed. At this time, Equation 1 satisfied the range of 10.54.

In Comparative Example 5, a negative electrode was manufactured in the same manner as Comparative Example 5, except that the thickness of Table 2 below and the range of Equation 1 were satisfied. For reference, the evaluated Examples and Comparative Examples were those in which the first negative electrode active material layer and the second negative electrode active material layer were 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 thickness of the entire first negative electrode active material layer and the second negative electrode active material layer formed on both sides.

First cathode active material layer Second cathode active material layer Equation 1 Thickness (㎛) Loading amount (mg/cm ² ) Thickness (㎛) Loading amount (mg/cm ² ) Comparative Example 5 98.2 8.012 11.2 0.908 11.4 Comparative Example 6 113.6 9.268 5.9 0.488 5.2 Comparative Example 7 93.4 7.62 12.8 1.04 13.7 Comparative Example 8 75.3 6.14 18.7 1.536 24.8

Comparative Example 9: Preparation of cathode

An active material layer composition was prepared using Si (average particle diameter (D50): 5㎛) as a silicon-based active material, a first conductive material, and polyacrylamide as a binder at a weight ratio of 70:20:10. A negative electrode slurry was prepared by adding distilled water as a solvent for forming the negative electrode slurry (solids concentration: 25% by weight).

The first conductive material uses carbon black C (specific surface area: 58 m ² /g, diameter: 37 nm).

As a mixing method, the first conductive material, binder, and water were dispersed at 2500 rpm for 30 min using a homo mixer, then the active material was added and dispersed at 2500 rpm for 30 min to prepare a slurry.

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

Comparative Example 10: Preparation of cathode

In Comparative Example 9, Si (average particle diameter (D50): 5㎛), SiO (average particle diameter (D50): 3.5㎛) as the active material layer composition, and polyacrylamide as the first conductive material and binder were used in the ratio of 52.5:17.5: A negative electrode was manufactured in the same manner as Comparative Example 1, except that the active material layer composition was prepared at a weight ratio of 20:10.

The first conductive material is carbon black C (specific surface area: 58m ² /g, diameter: 37nm), and the second conductive material is plate-shaped graphite (specific surface area: 17m ² /g, average particle diameter (D50): 3.5um). , the third conductive material is carbon nanotubes.

Comparative Example 11: Preparation of cathode

In Example 1, artificial graphite, a first conductive material, a third conductive material, and CMC:SBR as a binder were used as the second cathode slurry at a weight ratio of 95.5:0.98:0.02:1:2.5. A second negative active material layer composition was prepared using SiO (average particle diameter (D50): 5㎛) as a silicon-based active material, a second conductive material, a third conductive material, and polyacrylamide as a binder at a weight ratio of 80:9.6:0.4:10. Except, the negative electrode was manufactured in the same manner as in Example 1.

<Manufacture of secondary batteries>

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (average particle diameter (D50): 15㎛) as the positive electrode active material, carbon black (product name: Super C65, manufacturer: Timcal) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder. A positive electrode slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) as a solvent for forming positive electrode slurry at a weight ratio of :1.2:1.59 (solid concentration 78% by weight).

As a positive electrode current collector, the positive electrode slurry was coated at a loading amount of 439.1 mg/25 cm ² on both sides of an aluminum current collector (thickness: 12㎛), rolled, and dried in a vacuum oven at 130°C for 10 hours. A positive electrode was manufactured by forming a positive electrode active material layer (thickness: 105.5 μm) (positive electrode thickness: 117.5 μm, porosity 26%).

The secondary battery of Example 1 was manufactured by interposing a polyethylene separator between the positive electrode and the negative electrode of Example 1 and injecting electrolyte.

The electrolyte is made by adding 3% by weight of vinylene carbonate based on the total weight of the electrolyte to an organic solvent mixed with fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) at a volume ratio of 30:70, and LiPF as a lithium salt. ₆ was added at a concentration of 1M.

Secondary batteries were manufactured in the same manner as above except that the negative electrode of the above examples and comparative examples was used.

Experimental Example 1: Monocell lifespan evaluation

The lifespan of the secondary battery manufactured above was evaluated using an electrochemical charger and discharger, and the capacity maintenance rate was evaluated. The capacity retention rate was confirmed after 200 cycles of charging (0.33C CC/CV charging 4.2V 0.05C cut) and discharging (0.33C CC discharging 2.5V cut) conditions of the secondary battery.

The 200th capacity retention rate was evaluated using the following equation. The results are shown in Table 3 below.

Capacity maintenance rate (%) = {(discharge capacity in the 200th cycle)/(discharge capacity in the first cycle)} x 100

Mono cell Capacity Retention @ 200 cycle number (%) Example 1 92.5 Example 2 90.1 Example 3 88.0 Comparative Example 1 71.4 Comparative Example 2 84.4 Comparative Example 3 62.7 Comparative Example 4 81.1 Comparative Example 5 88.9 Comparative Example 6 91.8 Comparative Example 7 88.3 Comparative Example 8 70.9 Comparative Example 9 53.0 Comparative Example 10 63.5 Comparative Example 11 75.2

As can be seen in Table 3, it was confirmed that Examples 1 to 3 of the present invention had superior lifespan performance compared to Comparative Examples 1 to 4 and 8 to 11. When silicon-based materials, which have an effect on volume expansion and contraction due to charge and discharge, are used, the lifespan performance is somewhat inferior, and it can be seen that the higher the proportion of graphite-based materials, which do not have volume expansion and contraction, the consistently superior lifespan performance. there was.

Comparative Examples 2 and 3 are cases in which the compositions of the first negative electrode active material layer and the second negative electrode active material layer are the same as those of Example 1, but the thickness range of the first negative electrode active material layer is not satisfied. In the case of Comparative Example 3, the thickness of the first negative electrode active material layer was increased and the capacity characteristics were secured, but the content of the silicon-based active material included in the first negative active material layer increased, so it was confirmed that the lifespan performance was poor as in Comparative Example 4. there was.

In Comparative Examples 1 and 8, it was confirmed that the ratio of the silicon-based material contained in the upper layer was too high, resulting in inferior lifespan performance. In the case of Comparative Example 9 and Comparative Example 10, where the active material capacity was further increased, it was confirmed that the lifespan performance was further deteriorated, and since the silicon-based active material with a capacity 10 times that of graphite was evaluated in the same voltage range as graphite, the degree of expansion and contraction increased. This is the result.

In Comparative Example 11, the upper and lower layers were reversed, and the performance was poor due to the electrode detachment phenomenon occurring due to volume expansion and contraction of the lower layer in contact with the foil.

For reference, Comparative Examples 5 to 7 did not contain a silicon-based active material in the first negative active material layer, and showed similar lifespan performance as the Example, but in the rapid charging evaluation described later, the performance was very poor due to the absence of a silicon-based active material. I was able to confirm.

Experimental Example 2: Rapid charging evaluation

The secondary batteries manufactured above were subjected to rapid charging evaluation using an electrochemical charger and discharger, and the charging times were confirmed. Fast charging evaluation is performed after 3 cycles of 0.33C/0.33C, and the final 3rd discharge capacity is determined as the cell capacity. Afterwards, in the 4th cycle, it is first charged at 0.33C, and then 80% of the 3rd discharge capacity is discharged, that is, discharged at 0.33C until the voltage at which 20% of the cell's capacity remains, and then charged to 80% at 4.5C. I order it. In conclusion, an evaluation was conducted to determine the time it takes to charge the cell to 20-80% capacity, and the results are listed in Table 4.

Rapid charging time (min, @ 20~80% capacity) Example 1 12.61 Example 2 12.33 Example 3 12.05 Comparative Example 1 10.62 Comparative Example 2 13.37 Comparative Example 3 10.22 Comparative Example 4 11.14 Comparative Example 5 15.41 Comparative Example 6 16.27 Comparative Example 7 15.11 Comparative Example 8 13.35 Comparative Example 9 13.49 Comparative Example 10 15.90 Comparative Example 11 29.41

Because silicon-based active materials have a larger capacity 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. Comparatively, silicon-based active materials have lower resistance as a lower C rate is applied, and as the CC section during charging becomes longer, the charging time is reduced. Conversely, if the resistance is high, CV is applied as it quickly reaches 4.2V, which lowers the current and increases the charging time.

In Table 4, Examples 1 to 3, which contain a specific amount of silicon-based active material in the lower layer, have relatively low charging times. In the case of Comparative Examples 5 to 7 containing only graphite-based active materials in the lower layer, it was confirmed that the lifespan performance was excellent, but the fast charging performance was very inferior to that of Examples 1 to 3.

In Comparative Examples 1 and 8, it was confirmed that the charging performance improved as the ratio of the upper layer using silicone increased. However, as can be seen in Table 3, the results showed that the lifespan performance was very poor. Comparative Examples 9 and 10 used Pure Si, which has a large active material capacity, and were suitable for rapid charging, but the lifespan performance was also very poor. Additionally, it was confirmed that Comparative Example 11 was very inferior to rapid charging as the graphite layer was formed in the upper layer.

10: Second negative electrode active material layer
20: First negative electrode active material layer
30: Negative current collector layer

Claims (12)

Negative 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 opposite side of the first negative electrode active material layer in contact with the negative electrode current collector layer.
The first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material,
The second negative 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 at least one selected from the group consisting of carbon-based active material, silicon-based active material, metal-based active material capable of alloying with lithium, and lithium-containing nitride,
Based on 100 parts by weight of the first negative active material, the silicon-based active material is included in an amount of 5 parts by weight or less,
A negative electrode for a lithium secondary battery that satisfies the following formula 1:
[Equation 1]
0.1 ≤ [B / (A+B)]x100(%) ≤15
In equation 1 above,
A is the total thickness of the first negative 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. In claim 1,
The first negative electrode active material includes one or more mixtures selected from the group consisting of carbon-based active material, silicon-based active material, metal-based active material capable of alloying with lithium, and lithium-containing nitride, and the silicon-based active material is contained in an amount of 1 based on 100 parts by weight of the first negative electrode active material. A negative electrode for a lithium secondary battery weighing more than 5 parts by weight and less than 5 parts by weight. In claim 1,
The silicon-based active material is a negative electrode for a lithium secondary battery comprising one or more selected from the group consisting of SiOx (0<x<2), SiC, and Si alloy. In claim 1,
The silicon-based active material is SiOx (0<x<2); Or a negative electrode for a lithium secondary battery containing SiC. In claim 1,
A negative electrode for a lithium secondary battery, 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. In claim 1,
A negative electrode for a lithium secondary battery, wherein the total thickness of the second negative electrode active material layer is 1 μm or more and 20 μm or less. In claim 1,
The loading amount of the first negative active material layer composition is 5 mg/cm ² or more and 20 mg/cm ^{2 or} less,
A negative electrode for a lithium secondary battery, wherein the loading amount of the second negative electrode active material layer composition is 0.1 mg/cm ² or more and 5 mg/cm ² or less. In claim 1,
The first negative electrode active material layer composition includes a first negative electrode conductive material; And it further comprises at least one selected from the group consisting of a first negative electrode binder,
The second anode active material layer composition includes a second anode conductive material; and a second negative electrode binder. The method of claim 1, wherein the carbon-based active material includes graphite,
The graphite includes artificial graphite and natural graphite,
A negative electrode for a lithium secondary battery, wherein the weight ratio of the artificial graphite and natural graphite is 5:5 to 9.5:0.5. Preparing a negative electrode current collector layer;
forming a first negative electrode active material layer by applying a first negative electrode active material layer composition to one or both sides of the negative electrode current collector layer; and
A method of manufacturing a negative electrode for a lithium secondary battery comprising: applying a second negative electrode active material layer composition to a surface opposite to the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer, thereby forming a second negative electrode active material layer. ,
The second negative 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 at least one selected from the group consisting of carbon-based active material, silicon-based active material, metal-based active material capable of alloying with lithium, and lithium-containing nitride,
Based on 100 parts by weight of the first negative active material, the silicon-based active material is included in an amount of 5 parts by weight or less,
A method for manufacturing a negative electrode for a lithium secondary battery that satisfies the following formula 1:
[Equation 1]
0.1 ≤ [B / (A+B)]x100(%) ≤15
In equation 1 above,
A is the total thickness of the first negative 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. In claim 10,
Pre-lithiating the negative electrode on which the first negative electrode active material layer and the second negative electrode active material layer are formed on the negative electrode current collector,
Pre-lithiating the cathode includes a lithium electrolytic plating process; Lithium metal transfer process; Lithium metal deposition process; Or a method of manufacturing a negative electrode for a lithium secondary battery comprising a stabilized lithium metal powder (SLMP) coating process. anode;
A negative electrode for a lithium secondary battery according to any one of claims 1 to 9;
A separator provided between the anode and the cathode; and
A lithium secondary battery containing an electrolyte.