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

Abstract

The present application relates to a negative electrode for a lithium secondary battery, a method for producing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0136718, filed with the Korean Intellectual Property Office on October 21, 2022, and all its contents are incorporated herein by reference.

[0002] This application relates to a negative electrode for a lithium secondary battery, a method for manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including a negative electrode. [Background technology]

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

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

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

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

[0007] In particular, in recent years, in response to the demand for high-density energy batteries, Si / C and SiO2, which have more than 10 times the capacity of graphite-based materials, have become popular as negative electrode active materials.x Research is actively underway on methods to increase capacity by using silicon-based compounds such as [mention specific silicon compounds here] together. However, while silicon-based compounds are high-capacity materials and have superior capacity characteristics compared to conventionally used graphite, they rapidly expand in volume during the charging process, disrupting the conductive path and degrading battery performance, resulting in a decrease in capacity from the start. Furthermore, with silicon-based negative electrodes, uniform charging of lithium ions does not occur in the depth direction of the negative electrode during repeated charge and discharge cycles, and the reaction proceeds at the surface, accelerating surface degradation. Therefore, performance improvements are needed in terms of battery cycles.

[0008] Therefore, in order to resolve the aforementioned problems when using silicon-based compounds as negative electrode active materials, various methods are being discussed to suppress volume expansion itself, such as methods to adjust the driving potential, methods to further coat a thin film on the active material layer, and methods to adjust the particle size of the silicon-based compound, or methods to develop binders that suppress the volume expansion of silicon-based compounds to prevent the conduction path from being interrupted. Research is also underway to complement the life characteristics of silicon-based negative electrodes by limiting the proportion of silicon-based active material used during initial charging and discharging through a method of pre-lithifying the silicon-based active material layer, thereby giving it the role of a reservoir.

[0009] However, the aforementioned method may actually degrade battery performance, thus limiting its applicability. Furthermore, there are still limitations to the regular use of negative electrode batteries with a high silicon-based compound content. As the proportion of silicon-based active material in the silicon-based active material layer increases, the negative electrode surface reaction progresses, leading to problems.

[0010] Therefore, even when using silicon-based compounds as active materials, research is needed on methods that can prevent electrode surface degradation during the progression of charge and discharge cycles, and prevent the significant volume expansion that results in reduced lifespan. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 [Summary of the Invention] [Problems to be Solved by the Invention]

[0012] This application relates to a method that can prevent electrode surface deterioration during charge and discharge cycles, which are existing problems, while using a silicon-based active material for the negative electrode, and can further improve the volume expansion of the silicon-based active material.

[0013] Specifically, in this invention, through research, it was confirmed that when the negative electrode active material layer is composed of two layers instead of a single layer to prevent the electrode surface deterioration phenomenon and further improve the binder contained in the lower layer (the first negative electrode active material layer), the life characteristics can be improved. Accordingly, this application relates to a negative electrode for a lithium secondary battery, a method for manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Means for Solving the Problems]

[0014] One embodiment of this specification is a negative electrode for a lithium secondary battery including a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the first negative electrode active material layer facing the negative electrode current collector layer, wherein the first negative electrode active material layer includes a first negative electrode active material layer composition containing a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material layer composition containing a second negative electrode active material, the first negative electrode active material layer includes SiO x (x = 0) and SiO x selected from the group consisting of (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiO x(x = 0) contains 95 parts by weight or more, the second negative electrode active material contains one or more mixtures 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, the first negative electrode active material layer composition contains a first negative electrode binder, and the first negative electrode binder contains a polymer aqueous binder including a PAM-based or PAA-based binder; and a rubber-based binder; and satisfies the following formula 1, to provide a negative electrode for a lithium secondary battery.

[0015] [Formula 1] 1 ≦ X / Y < 4 In the above formula 1, X is the part by weight of the rubber-based binder based on 100 parts by weight of the first negative electrode binder, Y is the part by weight of the aqueous binder based on 100 parts by weight of the first negative electrode binder.

[0016] Also, in one embodiment of the present application, the first negative electrode active material layer may be formed on a partial surface or the entire surface of the negative electrode current collector layer, and the second negative electrode active material layer may be formed on a partial surface or the entire surface of the first negative electrode active material layer.

[0017] Also, in another embodiment, a step of preparing a negative electrode current collector layer; a step of applying a first negative electrode active material layer composition containing a first negative electrode active material on one surface or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and a step of applying a second negative electrode active material layer composition containing a second negative electrode active material on the opposite surface of the surface of the first negative electrode active material layer facing the negative electrode current collector layer to form a second negative electrode active material layer; is a method for manufacturing a negative electrode for a lithium secondary battery, wherein the first negative electrode active material contains at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), based on 100 parts by weight of the first negative electrode active material, the SiO x(x = 0) contains 95 parts by weight or more, the second negative electrode active material contains one or more mixtures 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, the first negative electrode active material layer composition contains a first negative electrode binder, and the first negative electrode binder contains a polymer aqueous binder including a PAM-based or PAA-based binder; and a rubber-based binder; and provides a method for manufacturing a negative electrode for a lithium secondary battery that satisfies the above formula 1.

[0018] Finally, a lithium secondary battery including a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte is provided.

Effect of the Invention

[0019] The negative electrode for a lithium secondary battery according to an 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 first negative electrode active material contained in the first negative electrode active material layer is SiO x (x = 0) and SiO x (0 < x < 2), and contains at least one selected from the group consisting of, based on 100 parts by weight of the first negative electrode active material, the SiO x (x = 0) contains 95 parts by weight or more, and the second negative electrode active material contained in the second negative electrode active material layer contains one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of alloying with lithium, and a lithium-containing nitride.

[0020] In particular, the second negative electrode active material contains at least one selected from the group consisting of a carbon-based active material, SiO x (0 < x < 2), SiC, and Si alloy, and may particularly contain SiO x (0 < x < 2).

[0021] The negative electrode for a lithium secondary battery according to the present application has a double-layer active material layer having the specific composition and content as described above. In particular, the first negative electrode active material layer is SiO xBy including a high content of (x=0), it retains the advantages of high capacity, high density, and rapid charging. Furthermore, by including silicon-based, carbon-based, or other active materials in the second negative electrode active material layer, degradation of the electrode surface during the progression of charge and discharge cycles can be prevented, and uniformity during pre-lithium conversion can also be improved.

[0022] Furthermore, the first negative electrode binder comprises a polymer aqueous binder including the PAM-based or PAA-based binder mentioned above, and a rubber-based binder, and is particularly characterized by satisfying the range of formula 1. That is, the proportion of aqueous binder for improving the dispersibility of the first negative electrode active material layer composition can be reduced, and a rubber-based binder can be further included, solving the process stability problem of deepening thermal shrinkage and enhancing the life characteristics. In addition, by using a first negative electrode binder of such a specific composition, volume expansion can be improved, the amount of conductive material can be reduced, the electrode thickness can be made even thinner, the capacitance characteristics can be maximized, and non-uniformity in the depth direction can also be improved.

[0023] In short, the negative electrode for lithium secondary batteries according to this application is characterized by adopting the advantages of electrodes that use a high content of Si particles as a single layer active material, while solving the disadvantages of such electrodes, namely surface degradation, uniformity issues during pre-lithiation, and lifespan characteristics, by constructing a double layer in which the first negative electrode active material layer and the second negative electrode active material layer are applied with specific compositions and content portions. [Brief explanation of the drawing]

[0024] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 3] This is a flowchart showing a wet-on-dry process according to one embodiment of this application. [Figure 4]This is a flowchart showing a wet-on-wet process according to one embodiment of this application. [Figure 5] This figure shows a method for measuring curl generation in an experimental example of this application. [Modes for carrying out the invention]

[0025] Before describing the present invention, let us first define some terms.

[0026] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0027] In this specification, "p~q" means the range "p or greater and q or less".

[0028] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mini II from BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0029] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the particle size distribution can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size as the particles pass through the laser beam is measured to calculate the particle size distribution.

[0030] In this specification, the meaning that a polymer contains a certain monomer in monomer units means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted in the same way as the polymer containing the monomer in monomer units.

[0031] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless specified as "homopolymer".

[0032] In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are the molecular weights in terms of polystyrene measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0033] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention pertains to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0034] One embodiment of this specification is a negative electrode for a lithium secondary battery including: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite surface of the surface of the first negative electrode active material layer facing the negative electrode current collector layer. The first negative electrode active material layer includes a first negative electrode active material layer composition containing a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material layer composition containing a second negative electrode active material, and the first negative electrode active material layer contains at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiO xThe present invention provides a negative electrode for a lithium secondary battery, comprising 95 parts by weight or more of (x=0), wherein the second negative electrode active material comprises a mixture of one or more materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides, and the first negative electrode active material layer composition comprises a first negative electrode binder, wherein the first negative electrode binder comprises a polymer aqueous binder including PAM-based or PAA-based materials, and a rubber-based binder, satisfying the following formula 1.

[0035] [Formula 1] 1 ≤ X / Y < 4 In the above formula 1, X is the weight of the rubber-based binder based on 100 weight parts of the first negative electrode binder, Y is the weight of the aqueous binder based on 100 parts by weight of the first negative electrode binder.

[0036] The negative electrode for lithium secondary batteries according to this application takes advantage of electrodes that use a high content of Si particles as a single-layer active material, and solves the problems of surface degradation, uniformity during pre-lithiation, and life characteristics that are disadvantages of such electrodes. In this way, the first negative electrode binder contains a polymer aqueous binder including the aforementioned PAM-based or PAA-based binder and a rubber-based binder, and is particularly characterized by satisfying the range of formula 1. That is, the proportion of aqueous binder for improving the dispersibility of the first negative electrode active material layer composition can be reduced, and a rubber-based binder can be further included, solving the problem of process stability where thermal shrinkage deepens, and enhancing life characteristics. Furthermore, by using a first negative electrode binder with such a specific composition, volume expansion can be improved, the amount of conductive material can be reduced, the electrode thickness can be made even thinner, capacity characteristics can be maximized, and non-uniformity in the depth direction can also be improved.

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

[0038] Figure 2 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of this application. Specifically, as shown in Figure 2, a first negative electrode active material layer 20 and a second negative electrode active material layer 10 may be formed on both sides of the negative electrode current collector layer 30. Alternatively, the arrangement may be 10>20>30>20>10, or moreover, if the first negative electrode active material layer and the second negative electrode active material layer are sequentially laminated on only one side of the negative electrode current collector layer, such as 10>20>30>20, 10>20>30>10, 10>20>30>10>20, the arrangement on the opposite side may be laminated in any way. Preferably, both sides of the negative electrode current collector layer have the same composition, and specifically, it may have a structure of 10>20>30>20>10.

[0039] The negative electrode for lithium secondary batteries of the present invention will be described in more detail below.

[0040] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the side of the first negative electrode active material layer opposite to the side in contact with the negative electrode current collector layer.

[0041] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0042] In one embodiment of the present application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less.

[0043] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0044] In one embodiment of the present application, the first negative electrode active material contains at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiO x (x = 0) may be contained in an amount of 95 parts by weight or more.

[0045] In one embodiment of the present application, the first negative electrode active material contains at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiO x (x = 0) is 95 parts by weight or more, preferably the SiO x (x = 0) is 97 parts by weight or more, more preferably 99 parts by weight or more, and may be contained in an amount of 100 parts by weight or less.

[0046] In one embodiment of this application, the first negative electrode active material can be pure silicon (Si) particles in particular. Using pure silicon (Si) as the first negative electrode active material means that, as described above, when based on 100 parts by weight of the total first negative electrode active material, it consists of pure Si particles (SiO) that are not bonded with other particles or elements. x This can mean that (x=0) is included in the aforementioned range.

[0047] The first negative electrode active material used in the first negative electrode active material layer of the present invention undergoes a very complex crystallographic change in the reaction of electrochemically absorbing, storing, and releasing lithium atoms. As the reaction of electrochemically absorbing, storing, and releasing lithium atoms progresses, the composition and crystal structure of silicon particles change to Si (crystal structure: Fd3m), LiSi (crystal structure: I41 / a), Li2Si (crystal structure: C2 / m), Li7Si2 (Pbam), Li 22 It transforms into Si5(F23), etc. Furthermore, due to the complex changes in crystal structure, the volume of silicon particles expands by approximately four times. Therefore, repeated charge-discharge cycles can cause the silicon particles to break down, and the formation of bonds between lithium atoms and silicon particles can damage the lithium atom insertion sites initially present in the silicon particles, potentially leading to a significant decrease in cycle life.

[0048] In one embodiment of this application, the first negative electrode active material is SiO x It can also start from (x=0).

[0049] The first negative electrode active material layer relating to this application contains the first negative electrode active material, specifically SiO x It contains pure silicon particles containing 95 parts by weight or more of (x=0). In this case, when it contains a high content of pure silicon particles, it has excellent capacity characteristics, and the lifespan reduction characteristics due to surface non-uniform reaction caused by this are resolved, and the output characteristics are improved and the rapid charging performance is improved by including the second negative electrode active material layer according to the present invention.

[0050] On the other hand, the average particle size (D50) of the first negative electrode active material of the present invention is 3 μm to 10 μm, specifically 4 μm to 8 μm, and more specifically 5 μm to 7 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles falls within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the first negative electrode active material is greater than or equal to the lower limit of the above range, the composite material consisting of the conductive material and binder in the negative electrode slurry provides excellent contact area between the silicon particles and the conductive material, increasing the likelihood of a sustained conductive network and increasing the capacity retention rate. On the other hand, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of non-uniform current density during charging and discharging.

[0051] In one embodiment of this application, the first negative electrode active material generally has a characteristic BET surface area. The BET surface area of ​​the first negative electrode active material is preferably 0.01 m². 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 The value is / g. The BET surface area is measured according to DIN 66131 (using nitrogen).

[0052] In one embodiment of this application, the first negative electrode active material may exist, for example, in a crystalline or amorphous form, and preferably not porous. The silicon particles are preferably spherical or fragmentary particles. Alternatively, but less preferably, the silicon particles may further have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0053] In one embodiment of this application, the silicon-based active material may have a non-spherical shape, and its degree of sphericity is, for example, 0.9 or less, for example 0.7 to 0.9, for example 0.8 to 0.9, for example 0.85 to 0.9.

[0054] In this application, the degree of sphericity is determined by the following formula 1-1, where A is the area and P is the boundary line.

[0055] [Formula 1-1] 4πA / P 2

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

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

[0058] The first negative electrode active material layer composition according to this application solves the problems of surface degradation during charging and discharging, uniformity during pre-lithification, and lifespan characteristics without reducing the overall capacity performance of the negative electrode, even when using a first negative electrode active material with significantly high capacity within the aforementioned range, by using a second negative electrode active material layer described later in combination.

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

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

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

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

[0063] The details regarding the first negative electrode conductive material are the same as those regarding the second negative electrode conductive material, which will be described later, and will therefore be described later.

[0064] In one embodiment of this application, the first negative electrode binder comprises a polymer aqueous binder including a PAM-based or PAA-based binder; and a rubber-based binder; and provides a negative electrode for a lithium secondary battery that satisfies the following formula 1.

[0065] [Formula 1] 1 ≤ X / Y < 4 In the above formula 1, X is the weight of the rubber-based binder based on 100 weight parts of the first negative electrode binder, Y is the weight of the aqueous binder based on 100 parts by weight of the first negative electrode binder.

[0066] Generally, one-component aqueous binders were used as binders for silicon-based anodes. That is, aqueous binders were used to disperse the rigid silicon-based active material, although they had low adhesive strength but improved dispersibility. However, because aqueous binders also have high rigidity, problems such as curling occurred due to stress acting on them during drying.

[0067] Therefore, it was found that when a specific binder satisfying the above composition and content is applied as the first negative electrode binder according to this application, dispersibility can be improved, adhesive strength can be satisfied, and the life characteristics of the negative electrode for lithium secondary batteries can be enhanced.

[0068] In one embodiment of this application, the first negative electrode binder may include a polymer aqueous binder having a Young's modulus of 1 × 10⁻⁶. 3 It may be MPa or higher.

[0069] In another embodiment, the polymer aqueous binder has a Young's modulus of 1 × 10⁻⁶ 3 MPa or higher, preferably 2 × 10 3 MPa, more preferably 5 × 10 3 It is MPa or higher, and 20 × 10 3 MPa or less, preferably 18 × 10 3 MPa or less, more preferably 15 × 10 3 It may be satisfied with a pressure of less than MPa.

[0070] The aforementioned polymer aqueous binder possesses both dispersibility for dispersing the negative electrode active material in a negative electrode slurry containing the negative electrode composition and adhesive strength for binding to the negative electrode current collector layer and negative electrode active material layer after drying, and its adhesive strength is not particularly high. In other words, the polymer aqueous binder according to this application satisfies the aforementioned Young's modulus and can be said to be a binder having a surface adhesion form.

[0071] In one embodiment of this application, the polymer aqueous binder is soluble in an aqueous solvent such as water and comprises at least one selected from the group consisting of polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacryl amide (PAM). Preferably, it may comprise at least one selected from the group consisting of polyacrylic acid (PAA) and polyacryl amide (PAM), more preferably polyacrylic acid (PAA) and polyacryl amide (PAM), in terms of having excellent resistance to volume expansion / contraction of the silicon-based active material.

[0072] More specifically, the polymer aqueous binder may be a PAM-based binder, in which case the PAM-based binder is a binder whose main component is PAM, and the ratio of PAM, PAA, and PAN can be adjusted, and the Young's modulus described above can be satisfied by appropriately changing the composition.

[0073] The polymer aqueous binder may also contain a polymer aqueous binder in which hydrogen atoms are replaced with Li, Na, or Ca, etc., in order to further improve dispersion in an aqueous solvent such as water during the production of a negative electrode slurry for forming the negative electrode active material layer, and to improve the binding force by more smoothly coating the active material.

[0074] The aforementioned polymer aqueous binder is hydrophilic and generally does not dissolve in electrolytes or electrolytes used in secondary batteries. This property allows for the imparting of strong stress or tensile strength to the polymer aqueous binder when applied to a negative electrode or lithium secondary battery, thereby effectively suppressing the volume expansion / contraction problem associated with the charging and discharging of silicon-based active materials.

[0075] In one embodiment of this application, the weight-average molecular weight of the polymer aqueous binder may be 100,000 g / mol or more and 1,000,000 g / mol or less.

[0076] In one embodiment of this application, the rubber-based binder has a strain of 15% or more, preferably 20% or more, more preferably 30% or more, most preferably 40% or more, and may also have a strain of 80% or less, preferably 70% or less, and even more preferably 60% or less.

[0077] In this case, the strain value of the rubber binder can be specifically realized within a range that satisfies the aforementioned range by adjusting the ST / BD ratio of the SBR binder to an appropriate range.

[0078] In one embodiment of this application, the rubber-based binder can be defined as a substance different from the polymer-based aqueous binder, which does not dissolve well in aqueous solvents such as water, but can be smoothly dispersed in aqueous solvents.

[0079] Specifically, the rubber-based binder having a strain of 15% or more may include at least one selected from the group consisting of styrene butadiene rubber (SBR), hydrogenated nitrile butadiene rubber (HNBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, and fluororubber. Preferably, it may include at least one selected from the group consisting of styrene butadiene rubber and hydrogenated nitrile butadiene rubber, and more preferably styrene butadiene rubber, as it is easily dispersed and has excellent phase stability.

[0080] Generally, rubber-based binders are materials with very high electrolyte wettability compared to polymer aqueous binders. When the aforementioned rubber-based binder is located near the surface of the silicon-based anode, the FEC solvent or LiPF6 salt that can form the SEI layer can be supplied rapidly, resulting in lower anode resistance.

[0081] In one embodiment of this application, formula 1 may satisfy 1 ≤ X / Y < 4, preferably 1.1 ≤ X / Y < 3.9, and more preferably 1.2 ≤ X / Y < 3.8.

[0082] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided in which X is 50 parts by weight or more and 95 parts by weight or less, and Y is 5 parts by weight or more and 50 parts by weight or less.

[0083] In another embodiment, X may be 50 parts by weight or more and 95 parts by weight or less, preferably 55 parts by weight or more and 90 parts by weight or less, and more preferably 55 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the first negative electrode binder.

[0084] In another embodiment, Y may be 5 to 50 parts by weight, preferably 10 to 45 parts by weight, and more preferably 20 to 45 parts by weight, based on 100 parts by weight of the first negative electrode binder.

[0085] As described above, the first negative electrode binder according to this application satisfies the aforementioned content requirements for both the polymer aqueous binder and the rubber binder, and has the characteristic of improving dispersibility and solving the problem of adhesive strength even when a silicon-based active material is used.

[0086] In other words, when a polymer aqueous binder is used alone, there is a risk of negative electrode warping, crack formation associated with warping, and a decrease in lifespan characteristics. Therefore, by including a rubber binder only within the range of Equation 1, the rubber binder dissolves well in electrolytes or electrolyte solutions commonly used in secondary batteries, and when used in combination with a polymer aqueous binder, the stress on the polymer aqueous binder can be relaxed to a certain level.

[0087] Therefore, the first negative electrode binder of the present invention has the characteristic that, by satisfying a specific weight ratio (range of Equation 1) of the water-based binder and the rubber-based binder, it can effectively resolve the volume expansion / contraction problem of the silicon-based active material and improve its lifespan characteristics, resolve the warping problem during thin-film negative electrode manufacturing, and also improve adhesive strength.

[0088] Furthermore, by including the aforementioned first negative electrode binder, volume expansion is improved, which reduces the amount of conductive material. This allows for even thinner electrodes, maximizing capacitance characteristics and improving non-uniformity in the depth direction.

[0089] In one embodiment of this application, the first 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 first negative electrode active material layer composition, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0090] In one embodiment of this application, the second negative electrode active material may include a mixture of one or more materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides.

[0091] In this case, the negative electrode for a lithium secondary battery is provided, wherein the silicon-based active material is present in an amount of 60 parts by weight or more, based on 100 parts by weight of the second negative electrode active material.

[0092] In another embodiment, based on 100 parts by weight of the second negative electrode active material, the silicon-based active material may be contained in an amount of 60 parts by weight or more, preferably 70 parts by weight or more, more preferably 80 parts by weight or more, and may be contained in an amount of 100 parts by weight or less. The second negative electrode active material may be composed of a silicon-based active material.

[0093] In the second negative electrode active material layer, when the parts by weight of the silicon-based active material are less than the above range, during the progress of charge and discharge cycles, rather, the second negative electrode active material layer acts as a resistance layer and the capacity retention rate decreases, thereby causing a problem that the resistance increase rate of the negative electrode becomes high.

[0094] In one embodiment of the present application, the silicon-based active material contained in the second negative electrode active material is SiO x (0 < x < 2), SiC, and at least one selected from the group consisting of Si alloys may be included.

[0095] In one embodiment of the present application, the silicon-based active material is SiO x (0 < x < 2); or a negative electrode for a lithium secondary battery containing SiC is provided.

[0096] In another embodiment, the silicon-based active material contained in the second negative electrode active material may contain SiO x (0 < x < 2).

[0097] In another embodiment, the silicon-based active material contained in the second negative electrode active material may contain SiC.

[0098] In another embodiment, the second negative electrode active material is a silicon-based active material, and the silicon-based active material is SiO x (0 < x < 2).

[0099] The negative electrode for lithium secondary batteries according to this application is composed of a double layer, and as described above, the second negative electrode active material layer contains the second negative electrode active material, and contains the first negative electrode active material described above, maintaining high capacity and high density characteristics while simultaneously solving problems of surface degradation during charging and discharging, uniformity during pre-lithiation, and life characteristics.

[0100] In one embodiment of this application, the carbon-based active material can be any carbon material commonly used for lithium secondary batteries, such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, or activated carbon. Specifically, it can be processed into spherical or dot-like forms for use.

[0101] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the carbon-based active material contains graphite, the graphite contains artificial graphite and natural graphite, and the weight ratio of the artificial graphite to the natural graphite is 5:5 to 9.5:0.5.

[0102] The artificial graphite according to one embodiment of the present invention may be in the form of primary particles, or it may be in the form of secondary particles formed by the aggregation of multiple primary particles.

[0103] As used in this invention, the term "initial particle" refers to the original particle from which other types of particles are formed, and multiple primary particles can aggregate, combine, or assemble to form secondary particles.

[0104] As used in this invention, the term "secondary particles" refers to larger, physically separable particles formed by the aggregation, bonding, or assembly of individual primary particles.

[0105] The aforementioned primary particles of artificial graphite may be produced by heat-treating one or more selected from the group consisting of needle cokes, mosaic cokes, and coaltar pitch.

[0106] The aforementioned artificial graphite is generally produced by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum-based heavy oil at temperatures above 2,500°C. After such graphitization, it can be used as a negative electrode active material after particle size adjustment such as pulverization and the formation of secondary particles. In the case of artificial graphite, the crystals are randomly distributed within the particles, and it has a lower degree of spheroidization and a somewhat pointed shape compared to natural graphite.

[0107] The artificial graphite used in one embodiment of the present invention may include commercially widely used MCMB (mesophase carbon microbeads), MPCF (mesophase pitch-based carbon fiber), graphitized block artificial graphite, or graphitized powder artificial graphite. The sphericity of the artificial graphite may be 0.91 or less, or 0.6 to 0.91, or 0.7 to 0.9.

[0108] Furthermore, the artificial graphite can have a particle size of 5 μm to 30 μm, preferably 10 μm to 25 μm.

[0109] Specifically, the D50 of the primary particles of the artificial graphite may be 6 μm to 15 μm, 6 μm to 10 μm, or 6 μm to 9 μm. When the D50 of the primary particles satisfies such a range, the primary particles can be formed to a degree of high graphitization, the orientation index of the negative electrode active material particles can be appropriately ensured, and the rapid charging performance can be improved.

[0110] The artificial graphite secondary particles can be formed by assembling primary particles. That is, the secondary particles may be structures formed by the aggregation of the primary particles through an assembly process. The secondary particles may contain a carbonaceous matrix that aggregates the primary particles. The carbonaceous matrix may contain at least one of soft carbon and graphite. The soft carbon may be formed by heat-treating pitch.

[0111] The carbonaceous matrix may be present in the secondary particles in an amount of 8% to 16% by weight, specifically 9% to 12% by weight. This range is lower than the carbonaceous matrix content typically used in artificial graphite secondary particles. This allows for control of the particle size of the primary particles within the secondary particles, enabling the production of structurally stable secondary particles even with a small amount of carbonaceous matrix required for assembly, and ensuring a uniform amount of primary particles constituting the secondary particles.

[0112] The artificial graphite secondary particles have a carbon coating layer on their surface, and the carbon coating layer may contain at least one of amorphous carbon and crystalline carbon.

[0113] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene and graphene.

[0114] The amorphous carbon can adequately maintain the strength of the coating layer and suppress the expansion of the natural graphite. The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source in chemical vapor deposition.

[0115] The aforementioned carbides of other organic substances may be carbides of organic substances selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or kedohexose, and combinations thereof.

[0116] The D50 of the artificial graphite secondary particles is 10 μm to 25 μm, specifically 12 μm to 22 μm, and more specifically 13 μm to 20 μm. When this range is met, the artificial graphite secondary particles can be uniformly dispersed in the slurry, and the battery charging performance can also be improved.

[0117] The tap density of the artificial graphite secondary particles is 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. When this range is met, it means that the packing of the artificial graphite secondary particles in the negative electrode is smooth, and thus the adhesion strength of the negative electrode can be improved.

[0118] The natural graphite may generally be in the form of plate-like aggregates before processing, and these plate-like particles can be manufactured into a spherical form with a smooth surface by post-processing such as particle crushing and reassembly processes, for use as an active material for electrode manufacturing.

[0119] The natural graphite used in one embodiment of the present invention may have a sphericity greater than 0.91 and 0.97 or less, or 0.93 to 0.97, or 0.94 to 0.96.

[0120] The aforementioned natural graphite may have a particle size of 5 μm to 30 μm, or 10 μm to 25 μm.

[0121] According to one embodiment of the present invention, the weight ratio of artificial graphite to natural graphite may be 5:5 to 9.5:0.5, or 5:5 to 9.3:0.7, or 5:5 to 9:1, or 6:4 to 9:1. When the weight ratio of artificial graphite to natural graphite falls within such a range, it may exhibit superior output and be advantageous in terms of lifespan and fast charging performance.

[0122] In one embodiment of this application, the planar conductive material used as the 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 the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form for use in order to facilitate the storage and release of lithium ions.

[0123] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be represented as plate-like graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather are substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0124] In other words, the use of plate-shaped graphite as a conductive material in this application means that it was used not to store or release lithium in a planar or plate-like form, but rather as a material to secure a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0125] On the other hand, in this application, the use of a carbon-based active material as an active material means that it was processed into a point-like or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0126] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, has a BET specific surface area of ​​0.1 m².2 4.5 m or more per g 2 It may satisfy the range of 4.5 m or less per g. Further, the plate-shaped graphite as the planar conductive material may have a planar BET specific surface area of 5 m 2 or more per g.

[0127] The metal-based active material may be, as a representative example thereof, a compound containing any one or two or more metal elements selected from the group consisting of Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti, Sb, Ga, Mn, Fe, Co, Ni, Cu, Sr, Ba, etc. These metal compounds may be used in any form such as a single substance, an alloy, an oxide (such as TiO2, SnO2), a nitride, a sulfide, a boride, an alloy with lithium, etc., but a single substance, an alloy, an oxide, and an alloy with lithium can achieve a higher capacity.

[0128] As described above, when the second negative electrode active material satisfies the above composition and content, a lithium secondary battery with improved various performances such as cycle life characteristics can be manufactured. That is, in the present application, the second negative electrode active material layer serves as a buffer layer, and in order to solve the surface deterioration problem during charge and discharge, the uniformity problem during pre-lithiation, and the life characteristic problem, the SiO x (0 < x < 2) and / or by including a carbon-based active material, the intense reaction with lithium ions on the surface of the second negative electrode active material layer can be suppressed.

[0129] Ultimately, the second negative electrode active material layer according to the present application has the above composition and content, solves the surface deterioration problem during charge and discharge cycle continuation, and can have the effect of pre-lithiation even if pre-lithiation does not occur up to the first negative electrode active material layer during pre-lithiation, and has the characteristic of being able to provide a negative electrode for a high-capacity and high-density lithium secondary battery.

[0130] In one embodiment of the present application, the second negative electrode active material provides a negative electrode for a lithium secondary battery that is 60 parts by weight or more based on 100 parts by weight of the second negative electrode active material layer composition.

[0131] In another embodiment, the second negative electrode active material is 60 parts by weight or more, preferably 65 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition, and may be 95 parts by weight or less, preferably 90 parts by weight or less, and even more preferably 85 parts by weight or less. Most preferably, it may be 75 parts by weight or more and 80 parts by weight or less.

[0132] The second negative electrode active material layer composition according to this application has the characteristic of enhancing lifespan characteristics without reducing the negative electrode's capacity performance, by using a second negative electrode active material within the aforementioned range that has lower capacity characteristics than the first negative electrode active material but exhibits less particle cracking during the progression of charge-discharge cycles or pre-lithiation. Furthermore, when the composition contains the aforementioned second negative electrode active material, the output characteristics can be improved, thereby resulting in improved rapid charging performance.

[0133] In one embodiment of this application, the second negative electrode active material layer provides a negative electrode for a lithium secondary battery comprising a second negative electrode active material layer composition including a second negative electrode active material; a second negative electrode conductive material; and a second negative electrode binder.

[0134] In this case, the second negative electrode conductive material may include at least one selected from the group consisting of point conductive material; linear conductive material; and planar conductive material.

[0135] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity to the negative electrode, is conductive without inducing chemical changes, and means a conductive material having point-like or spherical shapes. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and may preferably include carbon black in that it embodies high conductivity and has excellent dispersibility.

[0136] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 It may be less than / g.

[0137] In one embodiment of this application, the particle size of the dot-like conductive material is 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0138] In one embodiment of this application, the second negative electrode conductive material may include a planar conductive material.

[0139] The aforementioned planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. It can be described as a plate-type conductive material or a bulk-type conductive material.

[0140] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0141] In one embodiment of this application, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is met, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0142] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0143] In one embodiment of this application, the planar conductive material may be a high specific surface area planar conductive material with a high BET specific surface area, or a low specific surface area planar conductive material.

[0144] In one embodiment of this application, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without limitation as the planar conductive material. In particular, the planar conductive material according to this application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low specific surface area planar conductive material in which dispersion does not cause problems.

[0145] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​5 m². 2 It may be more than / g.

[0146] In another embodiment, the planar conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

[0147] In another embodiment, the planar conductive material is a high specific surface area planar conductive material with a BET specific surface area of ​​50 m². 2 / g or more 500m 2 / g or less, preferably 80mg 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0148] In another embodiment, the planar conductive material is a low specific surface area planar conductive material with a BET specific surface area of ​​5 m². 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0149] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in the form of a bundle or rope, in which multiple carbon nanotube units are arranged or intertwined in substantially the same orientation along their longitudinal axes. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be determined by the angle and structure in which the graphite sheet is wound. Compared to entangled type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during anode manufacturing, smoothly form a conductive network within the anode, and improve the conductivity of the anode.

[0150] In particular, the linear conductive material according to one embodiment of this application may be a single-walled carbon nanotube (SWCNT).

[0151] The aforementioned single-walled carbon nanotube is a material in which carbon atoms arranged in a hexagonal pattern form a tube. Depending on its unique chirality, it exhibits properties as an insulator, conductor, or semiconductor. The carbon atoms are linked by strong covalent bonds, resulting in a tensile strength approximately 100 times greater than that of steel, excellent flexibility and elasticity, and chemically stable properties.

[0152] 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 nm to 10 nm, or 1 nm to 5 nm, or 1 nm to 2 nm. When the average diameter of the single-walled carbon nanotubes satisfies such a range, the electrical conductivity of the negative electrode can be maintained even with a very small amount of single-walled carbon nanotubes, and a desirable viscosity and solid content can be obtained when manufacturing the conductive material dispersion. In the conductive material dispersion, the single-walled carbon nanotubes may exist in an entangled state (aggregates) where they are intertwined with each other. Therefore, the average diameter can be derived by first confirming the diameter of any entangled single-walled carbon nanotube aggregate extracted from the conductive material dispersion using SEM or TEM, and then dividing the diameter of the aggregate by the number of single-walled carbon nanotubes constituting the aggregate.

[0153] The BET specific surface area of ​​the single-walled carbon nanotube is 500 m². 2 / g~1,500m 2 / g, or 900m 2 / g~1,200m 2 It is / g, specifically 250m 2 / g~330m 2 It may also be / g. When the above range is satisfied, a conductive material dispersion with a desirable solid content is obtained, and the viscosity of the negative electrode slurry does not increase excessively. The BET specific surface area can be measured by the nitrogen adsorption BET method.

[0154] The aspect ratio of the single-walled carbon nanotube may be 50 to 20,000, or the length of the single-walled carbon nanotube may be 5 μm to 100 μm, or 5 μm to 50 μm. When the aspect ratio or length satisfies such a range, the specific surface area is at a high level, allowing the single-walled carbon nanotube to be strongly adsorbed to the active material particles within the negative electrode. This allows the conductive network to be smoothly maintained even during volume expansion of the negative electrode active material. The aspect ratio can be confirmed by observing the single-walled carbon nanotube powder through an SEM and calculating the average of the aspect ratios of 15 single-walled carbon nanotubes with a high aspect ratio and 15 single-walled carbon nanotubes with a low aspect ratio.

[0155] Compared to multi-walled and double-walled carbon nanotubes, the single-walled carbon nanotubes have an advantage in that they have a larger aspect ratio, longer length, and larger volume, allowing them to construct electrical networks even when used in small quantities.

[0156] In one embodiment of this application, the second negative electrode conductive material may satisfy the requirement of 1 part by weight or more and 40 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0157] In another embodiment, the second negative electrode conductive material may be 1 to 40 parts by weight, preferably 10 to 30 parts by weight, and more preferably 15 to 25 parts by weight, based on 100 parts by weight of the second negative electrode active material layer composition.

[0158] In one embodiment of this application, the second negative electrode conductive material includes a point conductive material; a planar conductive material; and a linear conductive material, wherein the ratio of the point conductive material:planar conductive material:linear conductive material may satisfy a ratio of 1:1:0.01 to 1:1:1.

[0159] In one embodiment of this application, the point-shaped conductive material may be in the range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the second negative electrode conductive material.

[0160] In one embodiment of this application, the planar conductive material may be in the range of 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the second negative electrode conductive material.

[0161] In one embodiment of this application, the linear conductive material may satisfy the range of 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 8 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the second negative electrode conductive material.

[0162] In one embodiment of this application, the second negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0163] In one embodiment of this application, the second negative electrode conductive material includes a linear conductive material and a planar conductive material, and the ratio of the linear conductive material to the planar conductive material may satisfy 0.01:1 to 0.1:1.

[0164] In one embodiment of this application, the second negative electrode conductive material particularly includes a linear conductive material and a planar conductive material, and by satisfying the above composition and proportion, the number of charge and discharge points increases without significantly affecting the life characteristics of existing lithium secondary batteries, and the battery has the characteristic of having a high C-rate and excellent output characteristics.

[0165] The first negative electrode conductive material according to this application provides a negative electrode for a lithium secondary battery, comprising at least a linear conductive material.

[0166] The second negative electrode conductive material according to this application provides a negative electrode for a lithium secondary battery that includes at least a linear conductive material.

[0167] In one embodiment of this application, the second negative electrode conductive material may be made of a linear conductive material.

[0168] The second negative electrode conductive material of this application has a completely different structure from the positive electrode conductive material applied to the positive electrode. Specifically, the second negative electrode conductive material of this application plays the role of capturing the contact points between silicon-based active materials, where the volume expansion of the electrodes is very large due to charging and discharging, while the positive electrode conductive material plays the role of a buffer during rolling while partially imparting conductivity, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0169] Furthermore, the second negative electrode conductive material in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and thus have the properties of improving output characteristics and imparting some conductivity. Their structure and role are completely different from conductive materials applied together with silicon-based active materials, as in the present invention.

[0170] In this case, the same provisions as those for the second negative electrode conductive material described above can be applied to the first negative electrode conductive material.

[0171] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the first negative electrode active material layer is 10 μm or more and 200 μm or less, and the thickness of the second negative electrode active material layer is 10 μm or more and 100 μm or less. The first negative electrode active material layer and the second negative electrode active material layer may be formed on both sides of the negative electrode current collector layer, and their thicknesses may be the same as those described above.

[0172] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided in which the loading amount (a) of the first negative electrode active material layer composition is at least twice the loading amount (b) of the second negative electrode active material layer composition.

[0173] In another embodiment, the loading amount (a) of the first negative electrode active material layer composition may satisfy the range of 1.5 times or more and 10 times or less, preferably 2.2 times or more and 6 times or less, of the loading amount (b) of the second negative electrode active material layer composition.

[0174] The loading amount can mean the weight of the composition for forming the negative electrode active material layer. Specifically, the loading amount of the composition can have the same meaning as the loading amount of the slurry containing the composition.

[0175] In one embodiment of the present application, the loading amount (a) of the first negative electrode active material layer composition is 2 mg / cm 2 or more and 5 mg / cm 2 or less, preferably 2.2 mg / cm 2 or more and 4 mg / cm 2 or less.

[0176] In one embodiment of the present application, the loading amount (b) of the second negative electrode active material layer composition is 0.5 mg / cm 2 or more and 1.5 mg / cm 2 or less, preferably 0.8 mg / cm 2 or more and 1.3 mg / cm 2 or less.

[0177] By having the first negative electrode active material layer composition and the second negative electrode active material layer composition have the loading amount, the ratio of the active materials contained in the first negative electrode active material layer and the second negative electrode active material layer can be adjusted. That is, the amount of the first negative electrode active material contained in the first negative electrode active material layer can be adjusted to optimize the capacity characteristics, and at the same time, the amount of the second negative electrode active material contained in the second negative electrode active material layer can be adjusted together so as not to reduce the capacity characteristics, and the surface reaction of the negative electrode can be suppressed to have the characteristic of enhancing the life characteristics.

[0178] In one embodiment of the present application, the negative electrode for the lithium secondary battery may be a pre-lithiated negative electrode.

[0179] In one embodiment of the present application, the first negative electrode active material layer may be formed on the entire surface of the negative electrode current collector layer, and the second negative electrode active material layer may be formed on the entire surface of the first negative electrode active material layer.

[0180] In one embodiment of the present application, a step of preparing a negative electrode current collector layer; a step of applying a first negative electrode active material layer composition containing a first negative electrode active material to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and a step of applying a second negative electrode active material layer composition containing a second negative electrode active material to the opposite surface of the surface of the first negative electrode active material layer facing the negative electrode current collector layer to form a second negative electrode active material layer; A method for manufacturing a negative electrode for a lithium secondary battery, wherein the first negative electrode active material includes at least one selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the first negative electrode active material, the SiO x (x = 0) contains 95 parts by weight or more, the second negative electrode active material includes one or more mixtures 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 layer composition includes a first negative electrode binder, and the first negative electrode binder includes a polymer aqueous binder including a PAM-based or PAA-based; and a rubber-based binder; A method for manufacturing a negative electrode for a lithium secondary battery that satisfies the above formula 1 is provided.

[0181] In the method for manufacturing the negative electrode, the composition and content included in each step can be applied with the above-mentioned content.

[0182] In one embodiment of the present application, a step of applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer is provided.

[0183] In other words, the aforementioned step is the step of forming an active material layer on the negative electrode current collector layer, and can be said to mean the step of forming the active material layer on the surface (lower layer) in contact with the current collector layer of the double layer structure. Furthermore, if the first negative electrode active material layer is formed on both sides of the negative electrode current collector layer, the second negative electrode active material layer can be applied to one or both sides of such first negative electrode active material layer.

[0184] In one embodiment of this application, applying the first negative electrode active material layer composition includes the step of applying and drying the first negative electrode slurry, which contains the first negative electrode active material layer composition and the negative electrode slurry solvent.

[0185] In this case, the solid content of the first negative electrode slurry may be in the range of 10% to 40%.

[0186] In one embodiment of this application, the step of forming the first negative electrode active material layer may include the steps of mixing the first negative electrode slurry and coating one or both sides of the negative electrode current collector layer with the mixed first negative electrode slurry, wherein the coating may be performed using coating methods commonly used in the industry.

[0187] In one embodiment of this application, the present invention provides a step of forming a second negative electrode active material by applying a second negative electrode active material layer composition to the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer.

[0188] In other words, the above step is the step of forming a second negative electrode active material layer on the first negative electrode active material layer, and can be said to be the step of forming the active material layer on the surface (upper layer) away from the current collector layer in the double layer structure.

[0189] In one embodiment of this application, applying the second negative electrode active material layer composition includes the step of applying and drying the second negative electrode slurry, which contains the second negative electrode active material layer composition and the negative electrode slurry solvent.

[0190] In this case, the solid content of the second negative electrode slurry may be in the range of 10% to 40%.

[0191] In one embodiment of this application, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the step of forming the second negative electrode active material layer includes the steps of: mixing the second negative electrode slurry; and coating the mixed second negative electrode slurry with the surface of the first negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer.

[0192] The aforementioned coating may be applied using coating methods commonly used in this industry.

[0193] The step of forming the second negative electrode active material layer can be similarly described in the explanation of the step of forming the first negative electrode active material layer.

[0194] One embodiment of this application provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry step; or a wet-on-wet step;

[0195] In one embodiment of this application, the wet-on-dry step may mean a step of applying a first negative electrode active material layer composition, partially or completely drying it, and then applying a second negative electrode active material layer composition on top of it.

[0196] Figure 3 is a flowchart of a wet-on-dry process according to one embodiment of this application. Specifically, in the wet-on-dry process, a first negative electrode slurry mixture (first negative electrode active material, first negative electrode conductive material, first negative electrode binder, first solvent) is prepared and applied to the negative electrode current collector layer. Then, the first negative electrode slurry mixture is dried to form the first negative electrode active material layer. After that, a second negative electrode slurry mixture is prepared and applied to the first negative electrode active material layer, and dried to form the second negative electrode active material layer. After that, each layer can be rolled and pressed together to form the negative electrode for a lithium secondary battery according to this application.

[0197] In one embodiment of this application, the wet-on-wet process means a process in which a first negative electrode active material layer composition is applied, and then a second negative electrode active material layer composition is applied on top of it without drying.

[0198] Figure 4 is a flowchart of a wet-on-wet process according to one embodiment of the present application. Specifically, in the wet-on-wet process, a first negative electrode slurry mixture is prepared and applied to the negative electrode current collector layer. Simultaneously, a second negative electrode slurry mixture is prepared and applied to the first negative electrode slurry mixture, and the first and second negative electrode slurry mixtures are dried. After that, each layer can be rolled and pressed to form the negative electrode for a lithium secondary battery according to the present application.

[0199] In one embodiment of this application, the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry step, the wet-on-dry step including the steps of: applying the first negative electrode active material layer composition; partially or completely drying the applied first negative electrode active material layer composition to form the first negative electrode active material layer; and applying the second negative electrode active material layer composition to the first negative electrode active material layer; thereby providing a method for manufacturing a negative electrode for a lithium secondary battery.

[0200] In one embodiment of this application, the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-wet step, the wet-on-wet step including the steps of: applying the first negative electrode active material layer composition; and applying the second negative electrode active material layer composition to the first negative electrode active material layer composition while the first negative electrode active material layer composition is still wet; thereby providing a method for manufacturing a negative electrode for a lithium secondary battery.

[0201] In particular, the wet-on-dry process involves applying the first negative electrode active material layer composition, partially or completely drying it, and then applying the second negative electrode active material layer composition on top of it. Through this process, the first negative electrode active material layer and the second negative electrode active material layer can have a clear boundary. As a result, the compositions contained in the first negative electrode active material layer and the second negative electrode active material layer do not mix, and the material can be constructed as a double layer.

[0202] In one embodiment of this application, the negative electrode slurry solvent can be used without limitation as long as it can dissolve the first negative electrode active material layer composition and the second negative electrode active material layer composition, and specifically, water or NMP can be used.

[0203] As a result of the aforementioned wet-on-wet process, a bonding region can be formed in which the first negative electrode active material layer and the second negative electrode active material layer are mixed. In this case, mutual mixing between the bonding region and the process can occur only when the viscosity of the first negative electrode active material layer composition is lower than the viscosity of the second negative electrode active material layer composition.

[0204] The aforementioned negative electrode for lithium secondary batteries has a first negative electrode active material layer containing SiO2 to enhance capacity characteristics. x The configuration includes (x=0) and the second negative electrode active material layer contains the aforementioned specific composition of silicon-based active material and / or carbon-based active material, thus retaining the advantages of rapid charging. Furthermore, because the second negative electrode active material has the aforementioned composition and is highly irreversible, it exhibits particularly advantageous effects during the pre-lithiation process in which the negative electrode is pre-filled. Compared to simply applying only the first negative electrode active material layer, having a second negative electrode active material with the aforementioned composition allows for a uniform pre-lithiation process at the upper end of the negative electrode, resulting in improved lifespan.

[0205] In one embodiment of this application, the porosity of the first and second negative electrode active material layers may be in the range of 10% to 60%.

[0206] In another embodiment, the porosity of the first and second negative electrode active material layers may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0207] The porosity of the porosity varies depending on the composition and content of the active material, conductive material, and binder contained in the first and second negative electrode active material layers, thereby ensuring that the electrical conductivity and resistance of the electrodes are within an appropriate range.

[0208] One embodiment of this application provides a lithium secondary battery comprising a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0209] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive and negative electrodes, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0210] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, which contains the positive electrode active material.

[0211] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0212] 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 (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≤ c1 ≤ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (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 ≤ 0.6), Ni-site type lithium nickel oxide represented by; chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≤ c3 ≤ 0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn).), lithium manganese composite oxides represented by; examples include LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The positive electrode may be Li metal (Li-metal).

[0213] In one embodiment of the present application, the positive electrode active material includes a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound includes single particles or secondary particles, and the average particle size (D50) of the single particles may be 1 μm or more.

[0214] For example, the average particle size (D50) of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 12 μm or less, more than 1 μm and 8 μm or less, or more than 1 μm and 6 μm or less.

[0215] Even when the single particle is formed with a small particle size (average particle size (D50) of 1 μm or more and 12 μm or less), it can exhibit excellent particle strength. For example, the single particle can have a strength of 650 kgf / cm². 2 With this force, the particle strength can be increased to 100 MPa to 300 MPa during rolling. This allows the single particle to be rolled to 650 kgf / cm². 2 Even when rolled with strong force, the phenomenon of increasing fine particles within the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0216] The single particle can be produced by mixing a transition metal precursor and a lithium raw material and firing the mixture. The secondary particle can be produced by a method different from that of the single particle, and its composition may be the same as or different from that of the single particle.

[0217] The method for forming the aforementioned single particles is not particularly limited, but they can generally be formed by increasing the firing temperature and over-firing. They can be manufactured by using additives such as grain growth promoters that aid in over-firing, or by changing the initiating substance.

[0218] For example, the firing is performed at a temperature at which single particles can be formed. In order to form these, firing must be performed at a higher temperature than that used for secondary particle production. For example, if the precursor composition is the same, firing must be performed at a temperature approximately 30°C to 100°C higher than that used for secondary particle production. The firing temperature for single particle formation can vary depending on the metal composition in the precursor. For example, when attempting to form single particles of a high-nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more, the firing temperature may be 700°C to 1000°C, preferably 800°C to 950°C. When the firing temperature satisfies the above range, a positive electrode active material containing single particles with excellent electrochemical properties can be produced. If the firing temperature is below 790°C, a positive electrode active material containing a secondary particulate lithium composite transition metal compound can be produced. If it exceeds 950°C, excessive firing may occur, the layered crystal structure may not be formed properly, and the electrochemical properties may deteriorate.

[0219] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by the aggregation of tens to hundreds of primary particles, and includes the concept of a single particle consisting of one primary particle and a pseudo-single particle, which is an aggregate of 30 or fewer primary particles.

[0220] Specifically, in the present invention, a single particle may be a single particle consisting of one primary particle or a pseudo-single particle in the form of an aggregate of 30 or fewer primary particles, and a secondary particle may be in the form of an aggregate of several hundred primary particles.

[0221] In one embodiment of this application, the lithium composite transition metal compound, which is the positive electrode active material, further contains secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0222] In the present invention, a single particle may be a single particle consisting of one primary particle or a pseudo-single particle in the form of an aggregate of 30 or fewer primary particles, and a secondary particle may be in the form of an aggregate of several hundred primary particles.

[0223] The aforementioned lithium-complex transition metal compounds may further contain secondary particles. Secondary particles refer to forms formed by the aggregation of primary particles and can be distinguished from the concept of single particles, which includes a single primary particle, a single particle, or a pseudo-single particle, which is an aggregate of 30 or fewer primary particles.

[0224] The particle size (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles is 0.05 m². 2 / g~10m 2 The value is / g, preferably 0.1m 2 / g~1m 2 The value is / g, and more preferably 0.3m 2 / g~0.8m 2 / g is also acceptable.

[0225] In a further embodiment of this application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0226] When the average particle size (D50) of the primary particles satisfies the aforementioned range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of aggregated primary particles forming lithium nickel oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially degrading the output characteristics.

[0227] According to a further embodiment of this application, the average particle size (D50) of the single particle is smaller than the average particle size (D50) of the secondary particle. As a result, even if the single particle is formed with a small particle size, it can have excellent particle strength, thereby mitigating the phenomenon of increasing fine particles in the electrode due to particle cracking, and thereby improving the battery life characteristics.

[0228] In one embodiment of this application, the average particle size (D50) of the single particle is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particle.

[0229] For example, the average particle size (D50) of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0230] When the average particle size (D50) of a single particle is smaller than the average particle size (D50) of a secondary particle, for example, when the above range is satisfied, the single particle can have excellent particle strength even if it is formed with a small particle size. This mitigates the phenomenon of increasing fine particles within the electrode due to particle fracture, resulting in improved battery life characteristics and improved energy density.

[0231] According to further embodiments of this application, the single particles are included in an amount of 15 to 100 parts by weight per 100 parts by weight of the positive electrode active material. The single particles may also be included in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight per 100 parts by weight of the positive electrode active material.

[0232] For example, the single particles may be present in amounts of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more per 100 parts by weight of the positive electrode active material. The single particles may be present in amounts of 100 parts by weight or less per 100 parts by weight of the positive electrode active material.

[0233] When the material contains single particles within the aforementioned range, it can exhibit excellent battery characteristics when combined with the aforementioned negative electrode material. In particular, when the single particles amount to 15 parts by weight or more, the phenomenon of increasing fine particles within the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery's lifespan.

[0234] In one embodiment of this application, the lithium composite transition metal compound may further contain secondary particles, the amount of which may be 85 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 0 parts by weight or more per 100 parts by weight of the positive electrode active material.

[0235] When the above range is satisfied, the above-described effect due to the presence of the single-particle positive electrode active material can be maximized. When the positive electrode active material includes secondary particles, its components may be the same as those exemplified by the above-described single-particle positive electrode active material or different components, and may mean a form in which single particles are aggregated.

[0236] In one embodiment of the present application, the positive electrode active material in 100 parts by weight of the positive electrode active material layer may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0237] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0238] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be constructed, it can be used without particular limitation as long as it has electronic conductivity without undergoing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds can be used.

[0239] In addition, the positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, etc. Among these, one kind alone or a mixture of two or more kinds may be used.

[0240] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, it can be used without particular limitation as long as it is used as a separator in a secondary battery. Particularly, it is preferable that it has a low resistance to the ion migration of the electrolyte while having excellent electrolyte moisture retention ability. Specifically, a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance can also be used, and it may be selectively used in a single-layer or multi-layer structure.

[0241] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the manufacture of lithium secondary batteries.

[0242] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0243] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0244] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be created, and this mixture is even more preferable.

[0245] The metal salt can be a lithium salt, and the lithium salt is a substance that dissolves easily in the non-aqueous electrolyte. For example, the anion of the lithium salt is F. - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2- (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - , (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - You can use one or more selected from the group consisting of the following.

[0246] In addition to the electrolyte components, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0247] One embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Since the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems. [Examples]

[0248] The following are preferred embodiments to aid in understanding the present invention. These embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such variations and modifications fall within the scope of the appended claims.

[0249] <Manufacturing example> Example 1 Manufacturing of negative electrodes Manufacturing of the first negative electrode active material layer A negative electrode slurry was prepared by adding Si (average particle size (D50): 5 μm) as a silicon-based active material, a second conductive material, a third conductive material, and a water-based binder, polyacrylamide (PAM), and a rubber-based binder, SBR, to distilled water as a solvent for negative electrode slurry formation in a weight ratio of 89:0:1:4.5:5.5 (solid content concentration 28% by weight).

[0250] The second conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 The third conductive material is carbon nanotubes, with a particle size of 3.5 μm (D50) and a mean particle size of 3.5 μm.

[0251] As for the specific mixing method, the second conductive material, the third conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes. After that, the silicon-based active material was added and dispersed again at 2500 rpm for 30 minutes to prepare the negative electrode slurry.

[0252] Manufacturing of the second negative electrode active material layer A second negative electrode active material layer composition was prepared using SiO (average particle size (D50): 6 μm) as a silicon-based active material, a second conductive material, a third conductive material, and polyacrylamide (PAM) as a water-based binder and SBR as a rubber-based binder in a weight ratio of 80:9.5:0.5:10:0. The second negative electrode slurry was produced by adding these materials to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 25% by weight).

[0253] The second conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the third conductive material is carbon nanotubes.

[0254] As the mixing method, the second conductive material, the third conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homomixer, and then the active material was added. After that, it was dispersed at 2500 rpm for 30 minutes to prepare the second negative electrode slurry.

[0255] As the negative electrode current collector layer, the negative electrode slurry was coated on both sides of a copper current collector (thickness: 26 μm) at a loading amount of 87.7 mg / 25 cm 2 Then, the second negative electrode slurry was coated on the first negative electrode active material layer at a loading amount of 20 mg / cm 2 It was rolled (roll press) and dried in a vacuum oven at 130 °C for 10 hours to form a first negative electrode active material layer (thickness: 41 μm) and a second negative electrode active material layer (thickness: 15 μm).

[0256] In Example 1, as the first negative electrode active material layer and the second negative electrode active material layer, a negative electrode satisfying the composition and content in Table 1 below was manufactured.

[0257]

Table 1

[0258] For reference, in Table 1, Comparative Examples 1 to 3 do not have the second negative electrode active material layer, that is, they are negative electrodes with a single-layer (Single layer) structure having a single negative electrode active material layer. That is, it corresponds to a negative electrode prepared by coating only the first negative electrode active material layer slurry on the negative electrode current collector layer and then drying it.

[0259] <Manufacture of secondary battery> As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2A cathode slurry was prepared by adding O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0260] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is coated on both sides with the positive electrode slurry at a rate of 537 mg / 25 cm². 2 The cathode was fabricated by coating with the specified loading amount, rolling (roll press), and drying in a vacuum oven at 130°C for 10 hours to form a cathode active material layer (thickness: 65 μm) (cathode thickness: 77 μm, porosity: 26%).

[0261] The secondary battery of Example 1 was fabricated by injecting an electrolyte between the positive electrode and the negative electrode of Example 1 via a polyethylene separation membrane.

[0262] The electrolyte in question was prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90 in an organic solvent, adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0263] Secondary batteries were fabricated in the same manner as described above, except that the negative electrodes of the above examples and comparative examples were used.

[0264] Experimental Example 1: Monocell Lifespan Evaluation The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries underwent cycle testing at 4.2-3.0V 1C / 0.5C, and the number of cycles required to achieve an 80% capacity retention rate was measured.

[0265] Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the 1st cycle)} × 100

[0266] The results are shown in Table 2 below.

[0267] Experimental Example 2: Measurement and Evaluation of Resistance Increase Rate In Experimental Example 1, during testing, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles. Then, the resistance was measured by discharging with a 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0268] For the aforementioned resistance increase rate measurement evaluation, data was calculated for 150 cycles, and the results are shown in Table 2 below.

[0269] Experiment Example 3: Evaluation of Rapid Charging The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were charged at 6C in CC-CV mode (4.2V, 5% cut-off) at SOC20 using an electrochemical charger / discharger at 35°C, and the charging time was measured. The results are shown in Table 2 below.

[0270] Experimental Example 4: Measurement of electrode curl As shown in Figure 5, the height of the center of the coated electrode was measured with the uncoated portion facing upwards, and the degree of warping was measured. In other words, this experiment measured the degree of curl that occurs when tensile stress acts on the coated portion during binder drying, causing it to indent, and the results are shown in Table 2 below.

[0271] [Table 2]

[0272] As can be seen from Table 2 above, in the case of Examples 1 to 6 of this application, the first negative electrode binder includes the aforementioned PAM-based or PAA-based polymer aqueous binder and a rubber-based binder, and in particular satisfies the range of Formula 1. That is, it has been confirmed that by reducing the proportion of the aqueous binder for improving the dispersibility of the first negative electrode active material layer composition and further including the rubber-based binder, the process stability problem of deepening thermal shrinkage can be solved, and the life characteristics are enhanced. Furthermore, it has been confirmed that by using a first negative electrode binder with such a specific composition, volume expansion is improved, the amount of conductive material can be reduced, the electrode thickness can be made even thinner, the capacitance characteristics can be maximized, and non-uniformity in the depth direction can also be improved.

[0273] Furthermore, Examples 1 to 6 correspond to cases where a second negative electrode active material layer is introduced, and it was confirmed that the lifespan and resistance performance are improved. In addition, in Examples 1 and 6, where the proportion of the second negative electrode active material in the second negative electrode active material layer is increased, it was confirmed that the rapid charging performance is improved.

[0274] Furthermore, a comparison of Examples 1 and 2 revealed that a higher proportion of rubber-based binder reduces the occurrence of electrode curling, which is advantageous for process stability.

[0275] Furthermore, when comparing Example 1 and Example 5, it was found that when the Si content of the first negative electrode active material layer is high, the thickness of the first negative electrode active material layer can be made thinner. In this case, as can be confirmed by the rapid charging performance, Example 1 was found to have superior rapid charging performance compared to Example 5. This is a result of the binder of the first negative electrode active material layer satisfying the combination described in this application, which allows for the formation of a thin first negative electrode active material layer.

[0276] Comparative Examples 1 to 3 described above are comparative examples where the negative electrode active material layer is a single layer. Specifically, these are single-layer negative electrode active material layers, and include cases where only the first negative electrode active material layer according to this application is present, where only a rubber-based binder is present, or where only a water-based binder is present. In these cases, it was confirmed that the life characteristics decreased and the resistance increase rate increased compared to the examples. This is due to the irregular surface reaction of the silicon-based negative electrode.

[0277] Comparative Examples 4 to 7 have a double-layer structure in which the negative electrode active material layer is formed with two layers, as in the example. However, Comparative Example 4 corresponds to the case where the first negative electrode active material layer has only an aqueous binder, Comparative Example 5 corresponds to the case where it has only a rubber binder, Comparative Example 6 corresponds to the case where it exceeds the range of Formula 1, and Comparative Example 7 corresponds to the case where it is less than the range of Formula 1.

[0278] In conclusion, in the cases of Comparative Examples 4 to 7, the first negative electrode active material layer according to this application did not satisfy the range of Equation 1, and it was confirmed that when the proportion of this application was not satisfied, the lifetime characteristics were lower compared to Examples 1 to 6, and the resistance increase rate was also higher.

[0279] Furthermore, as can be seen from Tables 1 and 2, it was confirmed that the thickness of the first negative electrode active material layer is determined by the Si content. Comparative Examples 1 to 3 correspond to a single-layer structure without a second negative electrode active material layer. In the case of SiO, since its capacity is smaller than that of Si, the thickness of the entire negative electrode active material layer can be made thinner compared to the examples of this application in order to achieve the same capacity. As a result, the rapid charging performance can be slightly better than that of the examples, but as can be seen from Table 2, it was confirmed that the life characteristics are significantly worse and the resistance increase rate is higher compared to the examples.

[0280] For reference, Comparative Examples 4 and 5 have the same silicon content and thickness range as Example 1 of this application. In this case, as can be seen in Table 2, the rapid charging performance is evaluated similarly to that of the example, but the first negative electrode active material layer according to this application does not satisfy the range of Equation 1, and it was confirmed that the life characteristics deteriorate significantly when the proportion of this application is not satisfied, and the resistance increase rate is also high. [Explanation of Symbols]

[0281] 10...Second negative electrode active material layer 20...first negative electrode active material layer 30 ···Negative electrode current collector layer 40. Negative electrode active material layer including the first negative electrode active material layer and the second negative electrode active material layer.

Claims

1. A negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on the opposite side of the first negative electrode active material layer from the side facing the negative electrode current collector layer; The first negative electrode active material layer comprises a first negative electrode active material layer composition containing a first negative electrode active material, and the second negative electrode active material layer comprises a second negative electrode active material layer composition containing a second negative electrode active material. The first negative electrode active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and based on 100 parts by weight of the first negative electrode active material, it contains 95 parts by weight or more of SiOx (x=0). The second negative electrode active material comprises a mixture of one or more materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides. The first negative electrode active material layer composition comprises a first negative electrode binder, The first negative electrode binder comprises a polymer aqueous binder containing PAM; and a rubber binder; and satisfies the following formula 1, and is a negative electrode for a lithium secondary battery: [Formula 1] 1 ≤ X / Y < 4 In the above formula 1, X is the weight of the rubber-based binder based on 100 parts by weight of the first negative electrode binder, and Y is the weight of the water-based binder based on 100 parts by weight of the first negative electrode binder.

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

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

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

5. The negative electrode for a lithium secondary battery according to claim 1, wherein 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.

6. The thickness of the first negative electrode active material layer is 10 μm or more and 200 μm or less. The anode for a lithium secondary battery according to claim 1, wherein the thickness of the second anode active material layer is 10 μm or more and 100 μm or less.

7. The aforementioned X is 50 parts by weight or more and 95 parts by weight or less. The negative electrode for a lithium secondary battery according to claim 1, wherein Y is 5 parts by weight or more and 50 parts by weight or less.

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

9. The first negative electrode active material layer is formed over the entire surface of the negative electrode current collector layer. The negative electrode for a lithium secondary battery according to claim 1, wherein the second negative electrode active material layer is formed over the entire surface of the first negative electrode active material layer.

10. The step of preparing the negative electrode current collector layer; A step of forming a first negative electrode active material layer by applying a first negative electrode active material layer composition containing the first negative electrode active material to one or both sides of the negative electrode current collector layer; and A method for manufacturing a negative electrode for a lithium secondary battery, comprising the step of applying a second negative electrode active material layer composition containing a second negative electrode active material to the surface of the first negative electrode active material layer opposite to the surface facing the negative electrode current collector layer to form a second negative electrode active material layer; The first negative electrode active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and based on 100 parts by weight of the first negative electrode active material, it contains 95 parts by weight or more of SiOx (x=0). The second negative electrode active material comprises a mixture of one or more materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metallic active materials that can be alloyed with lithium, and lithium-containing nitrides. The first negative electrode active material layer composition comprises a first negative electrode binder, The first negative electrode binder comprises a polymer aqueous binder containing PAM; and a rubber binder; and satisfies the following formula 1, a method for manufacturing a negative electrode for a lithium secondary battery: [Formula 1] 1 ≤ X / Y < 4 In the above formula 1, X is the weight of the rubber-based binder based on 100 parts by weight of the first negative electrode binder, and Y is the weight of the water-based binder based on 100 parts by weight of the first negative electrode binder.

11. The first negative electrode active material layer is formed over the entire surface of the negative electrode current collector layer. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 10, wherein the second negative electrode active material layer is formed over the entire surface of the first negative electrode active material layer.

12. The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-dry process. The aforementioned wet-on-dry process is Steps include applying the first negative electrode active material layer composition; The steps of forming the first negative electrode active material layer by partially or completely drying the coated first negative electrode active material layer composition; and Steps include applying the second negative electrode active material layer composition to the first negative electrode active material layer; A method for manufacturing a negative electrode for a lithium secondary battery according to claim 10 or 11, including the method described above.

13. The step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet-on-wet process. The aforementioned wet-on-wet process is, Steps include applying the first negative electrode active material layer composition; and A step of applying the second negative electrode active material layer composition to the first negative electrode active material layer composition while the first negative electrode active material layer composition is still wet; A method for manufacturing a negative electrode for a lithium secondary battery according to claim 10 or 11, including the method described above.

14. positive electrode; A negative electrode for a lithium secondary battery according to any one of claims 1 to 9; A separation membrane provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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