Silicon-based negative electrode

Abstract

Negative electrode for a secondary battery, consisting of: a current collector with a negative electrode and an active material layer with a negative electrode, which is formed on the current collector with a negative electrode, wherein the active material layer of the negative electrode comprises an active material of the negative electrode, which includes a silicon-based active material, and a conductive material, the conductive material contains carbon nanotubes with a diameter of 4 to 9 nm and 3 to 7 walls and the carbon nanotubes are contained in an amount of 3 to 9 wt.%, based on a total of 100 wt.% of the silicon-based active material.

Description

BACKGROUND1. Area

[0001] The present invention relates to a silicon-based negative electrode. 2. DESCRIPTION OF THE STATE OF THE ART

[0002] With the recent increase in technological development and demand for mobile devices, the demand for batteries as a power source has also increased rapidly. Therefore, various studies are being conducted on batteries that can meet various requirements. In particular, a lithium secondary battery with high energy density and excellent cycle and life characteristics is being actively investigated for powering the device.

[0003] A lithium secondary battery refers to a battery having a positive electrode comprising a positive electrode active material for storing / desorbing a lithium ion, a negative electrode comprising a negative electrode active material for storing / desorbing a lithium ion, and a non-aqueous electrolyte containing a lithium ion in an electrode assembly with a microporous separator disposed between the positive electrode and the negative electrode.

[0004] Lithium metal, lithium alloy, crystalline or non-crystalline carbon, carbon composites, silicon-based active materials, and the like are used as negative electrode active materials. Silicon-based active materials can improve the capacity of a secondary battery to achieve high energy density and are therefore used alone or in combination with other negative electrode active materials.

[0005] When using silicon-based active materials, a technology that uses single-walled carbon nanotubes and multi-walled carbon nanotubes as conductive materials has been proposed to improve conductivity. However, single-walled carbon nanotubes are difficult to synthesize and are cost-prohibitive, while multi-walled carbon nanotubes are inexpensive, but the amount required to ensure conductivity is excessively large and may be detrimental to the performance of the entire battery.

[0006] Accordingly, the development of a negative electrode containing a silicon-based active material that ensures an appropriate level of conductivity and is improved in terms of cost by reducing the cost price, and a secondary battery containing this material, is required. SUMMARY

[0007] One aspect of the present invention may provide a silicon-based negative electrode that may have a negative electrode slurry resistance value equal to or less than a predetermined value to ensure an appropriate level of conductivity.

[0008] According to one aspect of the present invention, a negative electrode for a secondary battery may comprise: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer comprises a silicon-based active material and a conductive material, the conductive material comprises carbon nanotubes having a diameter of 4 to 9 nm and 3 to 7 walls, and the carbon nanotubes are contained in an amount of 3 wt% to 9 wt% with respect to a total of 100 wt% of the silicon-based active material.

[0009] The carbon nanotubes may be present in an amount of 5 to 9 wt% based on the total weight of the silicon-based active material.

[0010] The conductive material may also contain one or more of the following materials: single-walled carbon nanotubes, multi-walled carbon nanotubes with 8 or more walls, and carbon black.

[0011] The conductive material may further contain the single-walled carbon nanotubes, and the single-walled carbon nanotubes may be contained in an amount of 0.15 wt% or more and 1 wt% or less with respect to the total weight of the silicon-based active material.

[0012] The weight ratio between the carbon nanotubes with a diameter of 4 to 9 nm and 3 to 7 walls and the single-walled carbon nanotubes can be 1:0.05 to 0.25.

[0013] The conductive material may further contain carbon black, and the carbon black may be contained in an amount of 6 wt% or more and 15 wt% or less based on the total weight of the silicon-based active material.

[0014] The weight ratio between the carbon nanotubes with a diameter of 4 to 9 nm and 3 to 7 walls and the soot can be 1:2 to 4.

[0015] The layer of active material of the negative electrode may also contain a binder.

[0016] A method for producing a negative electrode for a secondary battery may comprise: preparing a negative electrode slurry containing a silicon-based active material, a conductive material, and a binder; and applying the negative electrode slurry to a negative electrode current collector and drying the slurry, wherein the conductive material contains carbon nanotubes having a diameter of 4 to 9 nm and 3 to 7 walls, and the carbon nanotubes are contained in an amount of 3 wt% to 9 wt% based on a total of 100 wt% of the silicon-based active material.

[0017] The slurry resistance of the negative electrode slurry may be lower than the powder resistance of the silicon-based active material.

[0018] The mud resistance of the negative electrode mud can be 0.70 Ω-cm or less. DETAILED DESCRIPTION

[0019] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to various examples. However, the exemplary embodiments in the present invention can be modified in many different forms, and the scope of the invention should not be limited to the embodiments set forth herein.

[0020] The present invention relates to a silicon-based negative electrode.

[0021] According to one aspect of the present invention, there is provided a negative electrode for a secondary battery, comprising: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer comprises a silicon-based active material and a conductive material, the conductive material comprises carbon nanotubes having a diameter of 4 to 9 nm and 3 to 7 walls, and the carbon nanotubes are contained in an amount of 3 wt% to 9 wt% with respect to a total of 100 wt% of the silicon-based active material.

[0022] The negative electrode current collector is not particularly limited, as long as it has high conductivity without causing chemical changes in the battery. Specifically, copper, stainless steel, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used as the negative electrode current collector.

[0023] The negative electrode current collector can have a thickness of 3 to 100 μm, especially 4 to 40 μm, to realize a thin negative electrode. Fine irregularities can be formed on the surface of the negative electrode current collector to strengthen the bonding force of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous body, foam, and nonwoven body.

[0024] A negative electrode active material layer formed on at least one surface of the negative electrode current collector may contain a silicon-based active material. The silicon-based active material may comprise a compound represented by SiO x(0≤x<2), and since SiO2 does not react with a lithium ion and cannot store lithium, x can be within the range.

[0025] Without being limited to this, the average particle diameter (D 50 ) of the silicon-based active material may be 1 µm to 10 µm, particularly 2 µm to 6 µm, in order to promote the structural stability of an active material during charging and discharging and to form a conductive network to better maintain electrical conductivity, or to facilitate access to a binder that connects the active material and the current collector.

[0026] Meanwhile, the silicon-based active material can be contained in a variety of amounts, and, for example, can be contained in an amount of 5 wt% to 90 wt% in the negative electrode active material layer. To achieve a sufficiently high capacity of the silicon-based active material in a secondary battery, the silicon-based active material can be contained in an amount of 60 wt% to 90 wt%, and particularly 65 wt% to 75 wt%, in the negative electrode active material layer.

[0027] The negative electrode active material layer according to the present invention may contain a conductive material to support and improve the conductivity of a secondary battery, and the conductive material may contain thin-walled carbon nanotubes with a diameter of 4 to 9 nm and 3 to 7 walls. Furthermore, the thin-walled carbon nanotubes may have a BET specific surface area of ​​500 to 700 m². 2 / g. When thin-walled carbon nanotubes that meet the physical properties are used, the cost can be reduced compared to using single-walled carbon nanotubes, and the amount of thin-walled carbon nanotubes used is less than that of multi-walled carbon nanotubes, so a positive effect on the performance improvement of the entire battery can be achieved.

[0028] When thin-walled carbon nanotubes having the above-described physical properties are included as a conductive material, the thin-walled carbon nanotubes may be included in an amount of 3 to 9 wt%, particularly 5 to 9 wt%, with respect to a total of 100 wt% of the silicon-based active material. If the thin-walled carbon nanotubes are included in an amount of less than 3 wt% with respect to a total of 100 wt% of the silicon-based active material, which is outside the above range, adequate dispersion will not be performed, and the capacity retention rate of a secondary battery may be deteriorated.

[0029] According to another exemplary embodiment of the present invention, the conductive material may further include one or more of the following materials: single-walled carbon nanotubes, multi-walled carbon nanotubes having eight or more walls, and carbon black.

[0030] When single-walled carbon nanotubes are further included as a conductive material, the single-walled carbon nanotubes can be included in an amount of 0.15 wt% or more and 1 wt% or less with respect to a total of 100 wt% of the silicon-based active material. Reducing sludge resistance and improving capacity retention rates can also be promoted by adding 1 wt% or less of single-walled carbon nanotubes. Therefore, the amount of single-walled carbon nanotubes used, which are difficult to synthesize and have a high unit price, can be significantly reduced, and thus the cost of the entire process can be reduced.

[0031] Meanwhile, the weight ratio between the thin-walled carbon nanotubes with a diameter of 4 to 9 nm and 3 to 7 walls and the single-walled carbon nanotubes can be 1:0.05 to 0.25, and by including the thin-walled carbon nanotubes and the single-walled carbon nanotubes in the weight ratio, a reduction in slurry resistance and an improvement in capacity retention rate can be promoted.

[0032] When carbon black is further included as a conductive material, the carbon black may be included in an amount of 6 wt% or more and 15 wt% or less based on the total weight of the silicon-based active material. When carbon black is used as a mixture with the thin-walled carbon nanotubes, the resistance of a negative electrode slurry can be improved to increase conductivity. However, when carbon black is included in an amount of less than 6 wt%, the effect of improving conductivity is insignificant, and when carbon black is included in an amount of more than 15 wt%, it is not preferable from the point of view of commercial feasibility.

[0033] The negative electrode active material layer may contain a negative electrode binder to improve the bonding force between the negative electrode current collector and the negative active material or between the negative electrode active materials, if necessary, and the negative electrode binder may contain a water-based binder and a rubber-based binder.

[0034] The water-based binder may be dissolved in a water-based solvent such as water and may contain at least one of the following substances: polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyacrylamide (PAM) and carboxymethylcellulose (CMC).

[0035] The rubber-based binder can be defined as a binder that is not dissolved in the water-based solvent well, but is dispersed in the water-based solvent well. Specifically, the rubber-based binder may contain at least one rubber selected from styrene-butadiene rubber (SBR), hydrogenated nitrile-butadiene rubber (HNBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, and fluorine rubber. Specifically, it may contain at least one rubber selected from the group consisting of styrene-butadiene rubber and hydrogenated nitrile-butadiene rubber. For example, it may contain styrene-butadiene rubber, which is easy to disperse and has excellent phase stability.

[0036] The binder for the negative electrode is not particularly limited, but may be contained in an amount of 1 wt% or more and 15 wt% or less, particularly in an amount of 3 wt% or more and 10 wt% or less, for example, in an amount of about 5 wt%. Within this range, the binder can better bind the silicon-based active material to significantly reduce the problem of volume expansion of an active material. The binder can also be easily dispersed when preparing a slurry for forming the negative electrode active material layer, and the coatability and phase stability of the slurry can be improved.

[0037] A method for producing a negative electrode for a secondary battery comprises preparing a negative electrode slurry containing a silicon-based active material, a conductive material, and a binder; and applying the negative electrode slurry to a negative electrode current collector and drying the slurry, wherein the conductive material contains thin-walled carbon nanotubes having a diameter of 4 to 9 nm and 3 to 7 walls, and the carbon nanotubes are contained in an amount of 3 wt% to 9 wt% with respect to a total of 100 wt% of the silicon-based active material.

[0038] The negative electrode slurry further contains a solvent, and as the solvent, at least one of distilled water, ethanol, methanol, and isopropyl alcohol can be used to facilitate the dispersion of the negative electrode active material, the negative electrode conductive material, and the negative electrode binder, and distilled water can be used preferably.

[0039] Without being limited thereto, the solvent for forming the negative electrode slurry may be included so that the concentration of the solid content including the negative electrode active material, the negative electrode conductive material, and the negative electrode binder is 30 to 70 wt%, particularly 40 to 50 wt%, taking into account the viscosity, coatability, dispersibility, and the like of the negative electrode slurry.

[0040] Since the silicon-based active material, the conductive material, and the negative electrode current collector are as described above, a detailed description is omitted below.

[0041] Meanwhile, the slurry resistance of the negative electrode slurry containing the silicon-based active material, the conductive material, and a residual solvent can be lower than the powder resistance of the silicon-based active material. Since the silicon-based active material has a problem of low conductivity, it is preferable that the slurry resistance value of the negative electrode slurry be lower than the powder resistance value of the silicon-based active material. For example, since the powder resistance of SiO x is about 0.73 Ω-cm, the mud resistance value of the negative electrode mud may be 0.70 Ω-cm or less, for example, 0.61 Ω-cm or less.

[0042] The mud resistance value is derived here without actually fabricating the negative electrode with the silicon-based active material, so that the electrode performance can be predicted simply by measuring the mud resistance of the negative electrode mud.

[0043] According to another aspect of the present invention, a secondary battery with the negative electrode is provided. Specifically, the secondary battery according to an exemplary embodiment of the present invention includes the above-described negative electrode; a positive electrode that is a counter electrode to the negative electrode; a separator disposed between the negative electrode and the positive electrode; and an electrolyte.

[0044] The positive electrode is provided with a layer of a positive electrode active material formed by applying a slurry containing a positive electrode active material, a binder, and a conductive material, and drying the slurry. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in a battery. Specifically, aluminum, stainless steel, nickel, titanium, sintered carbon, copper, or stainless steel surface-treated with carbon, nickel, titanium, silver, and the like, an aluminum-cadmium alloy, and the like can be used as the positive electrode current collector. In addition, the positive electrode current collector can generally have a thickness of 3 to 500 μm.

[0045] The active material of the positive electrode is a compound for reversibly intercalating and deintercalating lithium and may in particular comprise a lithium transition metal composite oxide comprising at least one metal consisting of nickel, cobalt, manganese and aluminum, and lithium, in particular a lithium transition metal composite oxide comprising a transition metal comprising nickel, cobalt and manganese and lithium.

[0046] The positive electrode active material may be contained in an amount of 80 wt% to 99 wt%, e.g., 92 wt% to 98.5 wt%, in the positive electrode active material layer, taking into account sufficient capacity and the like of the positive electrode active material.

[0047] The positive electrode active material layer may further contain a positive electrode binder. The positive electrode binder is a component that promotes the bonding of the active material and the conductive material, and the like, as well as the bonding of the positive active electrode to the current collector. Specifically, the positive electrode binder may be at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and may specifically include polyvinylidene fluoride.

[0048] In addition, the active material layer of the positive electrode may contain one or more conductive materials from the group consisting of graphite, carbon black and conductive oxides.

[0049] The separator separates the negative electrode from the positive electrode and provides a migration channel for lithium ions. It can be used without any special restrictions as long as it is normally used as a separator in a lithium secondary battery. In particular, a separator that has low resistance to ion migration of an electrolyte and excellent impregnation ability of the electrolyte solution can be used.

[0050] Specifically, a porous polymer film, e.g., a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a two- or multi-layer laminated structure thereof, may be used. Furthermore, a conventional porous nonwoven fabric, e.g., a high-melting-point glass fiber, a nonwoven fabric made of a polyethylene terephthalate fiber, and the like, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material for ensuring thermal resistance or mechanical strength may be used, optionally as a single- or multi-layer structure.

[0051] The electrolyte may include, but is not limited to, organic-based liquid electrolytes, inorganic-based liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, and the like.

[0052] The negative-electrode secondary battery according to the present invention is useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in electric vehicle fields such as hybrid electric vehicles (HEVs), and the like, and can be used particularly as a configuration cell of a medium-sized battery module. Accordingly, an exemplary embodiment of the present invention also provides a medium-sized battery module including the above-described secondary battery as a unit cell.

[0053] The medium-sized battery module as such can be used in an energy source that requires large power and large capacity, such as an electric vehicle, a hybrid electric vehicle, and an electric energy storage system.

[0054] The present invention will now be described in detail with reference to examples. The following examples serve to further describe the present invention, but are not limited thereto. Example 1. Sludge preparation and sludge inventory measurement. Preparation Example 1

[0055] 6 wt.% of a silicon-based oxide (SiO x) with a powder resistance of 0.73 Ω-cm as the negative electrode active material and 0.3 wt% of 5-walled, 5-nm-diameter thin-walled carbon nanotubes (TWCNT) as the conductive material were added to water as the solvent, and 1.3 wt% of carboxymethylcellulose (CMC) was added thereto to prepare a negative electrode slurry. Preparation Example 2

[0056] A negative electrode slurry was prepared in the same manner as in Preparation Example 1, except that TWCNT was added at a content of 0.20 wt%. Preparation Example 3

[0057] A negative electrode slurry was prepared in the same manner as in Preparation Example 1, except that TWCNT was added at a content of 0.25 wt%. Preparation Example 4

[0058] A negative electrode slurry was prepared in the same manner as in Preparation Example 1, except that TWCNT was added at a content of 0.50 wt%. Comparative preparation example 1

[0059] A negative electrode slurry was prepared in the same manner as in Preparation Example 1, except that no TWCNT was added.

[0060] A PET film was coated with each slurry prepared in Preparation Examples 1 to 4 and Comparative Example 1 and dried at a temperature of 100 °C for 30 minutes, the slurry resistance was measured by a 4-probe method, and each measured slurry resistance value is listed in Table 1. [Table 1] TWCNT content (wt%) Manure resistance (Ωcm) Preparation Example 1 0.3 0.23 Preparation Example 2 0.20 0.61 Preparation Example 3 0.25 0.21 Preparation Example 4 0.50 0.07 Comparative preparation example 1 0 (no conductive material) Immeasurable

[0061] From Table 1, it can be seen that Preparation Examples 1 to 4, to which TWCNT were added, had a slurry resistance value of less than 0.73 Ω-cm, which is comparable to the powder resistance of the silicon-based oxide (SiO x ) as the negative electrode active material. Meanwhile, Comparative Example 1, which did not contain TWCNTs, showed a sludge resistance value that was too high to measure. Preparation Example 5

[0062] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.01 wt% of SWCNT was added as a conductive material. Preparation Example 6

[0063] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.02 wt% of SWCNT was added as a conductive material. Preparation Example 7

[0064] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.03 wt% of SWCNT was added as a conductive material. Preparation Example 8

[0065] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.035 wt% of SWCNT was added as a conductive material. Preparation Example 9

[0066] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.04 wt% of SWCNT was added as a conductive material. Preparation Example 10

[0067] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.05 wt% of SWCNT was added as a conductive material.

[0068] A PET film was coated with each slurry prepared in Preparation Examples 5 to 10 and dried at a temperature of 100 °C for 30 minutes. The resistance of the slurry was measured using a 4-probe method, and each measured resistance value of the slurry is listed in Table 2. [Table 2] Additional SWCNT content (wt%) Manure resistance (Ωcm) Preparation Example 5 0.01 0.32 Preparation Example 6 0.02 0.18 Preparation Example 7 0.03 0.11 Preparation Example 8 0.035 0.12 Preparation Example 9 0.04 0.09 Preparation Example 10 0.05 0.08 Preparation Example 11

[0069] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.4 wt% of carbon black was added as a conductive material. Preparation Example 12

[0070] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.6 wt% of carbon black was added as a conductive material. Preparation Example 13

[0071] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.8 wt% of carbon black was added as a conductive material. Preparation Example 14

[0072] A negative electrode slurry was prepared in the same manner as in Preparation Example 2, except that 0.2 wt% of carbon black was added as a conductive material.

[0073] A PET film was coated with each slurry prepared in Preparation Examples 11 to 14 and dried at a temperature of 100 °C for 30 minutes. The resistance of the slurry was measured using a 4-probe method, and each measured resistance value of the slurry is listed in Table 3. [Table 3] Additional carbon black content (wt%) Manure resistance (Ωcm) Preparation Example 11 0.4 0.46 Preparation Example 12 0.6 0.31 Preparation Example 13 0.8 0.35 Preparation Example 14 0.2 0.6

[0074] From Tables 2 and 3, when SWCNT and carbon black were further added as conductive materials, the mud resistance value was below 0.61 Ω-cm, which was the same as the mud resistance value of Preparation Example 2, thus confirming that the mud resistance value can be further reduced by adding a conductive material. 2. Manufacturing coin cells and measuring the capacity retention rateExample 1

[0075] A 10 µm thick copper foil current collector was coated with the negative electrode slurry prepared in Preparation Example 1 to prepare a negative electrode plate. The negative electrode plate with the finished coating was dried at 100 °C for 1 hour and rolled to prepare a negative electrode plate with a density of 1.5 g / cm3.

[0076] The thus prepared negative electrode plate was heat-treated at 100°C for 1 hour or more in a vacuum atmosphere and cut into a circle with a diameter of 16 mm to prepare a negative electrode for a coin cell. Example 2

[0077] A negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Preparation Example 2 was used. Example 3

[0078] A negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Preparation Example 3 was used. Example 4

[0079] A negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Preparation Example 4 was used. Example 5

[0080] A negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Preparation Example 5 was used. Example 6

[0081] A negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Preparation Example 8 was used. Example 7

[0082] A negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Preparation Example 9 was used. Example 8

[0083] A negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Preparation Example 10 was used. Comparative Example 1

[0084] A negative electrode was prepared in the same manner as in Example 1 except that the slurry prepared in Comparative Example 2 was used. Comparative Example 2

[0085] A negative electrode slurry was prepared in the same manner as in Preparation Example 1 except that 3.0 wt% of graphite was added instead of TWCNT as a conductive material, and then the negative electrode slurry was used to prepare a coin cell in the same manner as in Example 1.

[0086] The same positive electrode was laminated with each negative electrode prepared in Examples 1 to 8 and Comparative Examples 1 and 2 and a separator with a thickness of 25 μm (SKIE technology, 525HV) as a boundary, and an electrolyte solution was injected and compression was performed, thereby manufacturing a coin cell with a specification of 2032.

[0087] The capacity retention rate (%) of the coin cells of Examples 1 to 8 and Comparative Examples 1 and 2 at 100 cycles was determined at 45 °C with a C charge rate of 0.3 C and a C discharge rate of 0.5 C, and the results are shown in Table 4. [Table 4] Capacity retention rate (0.3 C-0.5 C) (%) @100 times Example 1 91.8 Comparison example 1 80.5 Example 2 83.4 Example 3 82.9 Example 4 85.5 Comparison example 2 86.9 Example 5 88.7 Example 6 89.3 Example 7 87.7 Example 8 88.7

[0088] In Table 4, it is confirmed that the battery prepared in Example 1 has a significantly excellent capacity retention rate. Furthermore, with reference to Examples 1 and 4 to 8, it is confirmed that the negative electrode prepared by mixing a small amount of SWCNT with TWCNT was used, thereby improving the sludge resistance and capacity retention rate.

[0089] The negative electrode according to an exemplary embodiment of the present invention has a resistance value of the negative electrode slurry at or below a predetermined value, thereby ensuring excellent conductivity. Furthermore, the performance of the electrode can be predicted by measuring the resistance of a conductive material and a thickener or slurry composed of a simpler composition without actually preparing an electrode. Since it is not necessary to actually prepare an electrode, process and time can be saved.

[0090] In the above, the exemplary embodiments in the present invention have been described in detail, however, the scope of a right of the present invention is not limited thereto, and it is obvious to a person skilled in the art that various modifications and changes are possible within the scope without departing from the technical idea of ​​the present invention.

[0091] Although exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations may be made without departing from the scope of the present invention as defined by the appended claims.

Claims

[1] Negative electrode for a secondary battery, consisting of: a current collector with a negative electrode and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material comprising a silicon-based active material and a conductive material, the conductive material contains carbon nanotubes with a diameter of 4 to 9 nm and 3 to 7 walls and the carbon nanotubes are contained in an amount of 3 to 9 wt.%, based on a total of 100 wt.% of the silicon-based active material. [2] The negative electrode for a secondary battery according to claim 1, wherein the carbon nanotubes are contained in an amount of 5 wt% to 9 wt% based on a total of 100 wt% of the silicon-based active material. [3] A negative electrode for a secondary battery according to claim 1 or 2, wherein the conductive material further contains one or more of the following materials: single-walled carbon nanotubes, multi-walled carbon nanotubes having 8 or more walls, and carbon black. [4] The negative electrode for a secondary battery according to claim 1 or 2, wherein the conductive material further contains the single-walled carbon nanotubes, and the single-walled carbon nanotubes are contained in an amount of 0.15 wt% or more and 1 wt% or less with respect to a total of 100 wt% of the silicon-based active material. [5] The negative electrode for a secondary battery according to claim 4, wherein the weight ratio between the carbon nanotubes having a diameter of 4 to 9 nm and 3 to 7 walls and the single-walled carbon nanotubes is 1:0.05 to 0.

25. [6] A negative electrode for a secondary battery according to claim 1 or 2, wherein the conductive material further contains carbon black, and the carbon black is contained in an amount of 6 wt% or more and 15 wt% or less based on a total of 100 wt% of the silicon-based active material. [7] The negative electrode for a secondary battery according to claim 6, wherein the weight ratio between the carbon nanotubes having a diameter of 4 to 9 nm and 3 to 7 walls and the carbon black is 1:2 to 4. [8] A negative electrode for a secondary battery according to any one of claims 1 to 7, wherein the negative electrode active material layer further contains a binder. [9] Negative electrode for a secondary battery comprising: a current collector with a negative electrode and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer contains a negative electrode active material comprising a silicon-based active material and a conductive material, the conductive material contains thin-walled carbon nanotubes and the thin-walled carbon nanotubes are contained in an amount of 3 to 9 wt.%, based on a total of 100 wt.% of the silicon-based active material. [10] A secondary battery having the negative electrode according to any one of claims 1 to 9.