KR20200107740A - Negative electrode, secondary battery comprising the negative electrode - Google Patents

Abstract

The present invention relates to a negative electrode to increase the capacity and lifespan of a battery, and a secondary battery including the same. According to the present invention, the negative electrode comprises a negative electrode active material layer and the negative electrode active material layer comprises a negative electrode active material and a conductive material. The negative electrode active material includes SiO_x(0 <= x < 2) particles and the conductive material includes secondary particles, in which one portion of one graphene sheet is connected to one portion of another graphene sheet adjacent to graphene sheet, and a carbon nanotube structure in which 2-5,000 single-wall carbon nanotube unit bodies are coupled to each other. The oxygen content of the secondary particles is 1-10 wt% with respect to the total weight of the secondary particles, a specific surface area of the secondary particles measured by a nitrogen adsorption BET method is 500-1,000 m^2/g, and 0.01-0.1 wt% of the carbon nanotube structure is included in the negative electrode active material layer.

Description

A negative electrode and a secondary battery including the negative electrode TECHNICAL FIELD [NEGATIVE ELECTRODE, SECONDARY BATTERY COMPRISING THE NEGATIVE ELECTRODE]

The present invention includes a negative active material layer, the negative active material layer includes a negative active material and a conductive material, the negative active material includes SiO _x (0≦x<2) particles, and the conductive material is one graphene sheet Secondary particles in which a portion of the graphene is connected to a portion of the adjacent graphene sheet; And a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, wherein the oxygen content of the secondary particles is 1% to 10% by weight based on the total weight of the secondary particles. , The specific surface area of the secondary particles measured by the nitrogen adsorption BET method is 500m ² /g to 1100m ² /g, the carbon nanotube structure is a negative electrode contained in an amount of 0.01% to 1.0% by weight in the negative active material layer, and It relates to a secondary battery including this.

Recently, as technology development and demand for mobile devices increase, the demand for batteries as an energy source is rapidly increasing, and accordingly, research on batteries that can meet various demands has been conducted in various ways. In particular, research on a lithium secondary battery having high energy density and excellent lifespan and cycle characteristics as a power source of such a device is actively being conducted.

A lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating/detaching lithium ions, a negative electrode including a negative active material capable of intercalating/deintercalating lithium ions, and an electrode with a microporous separator interposed between the positive electrode and the negative electrode It means a battery in which a non-aqueous electrolyte containing lithium ions is included in the assembly.

On the other hand, since the negative electrode active material alone cannot secure the conductivity of the negative electrode, there is a problem in that the resistance of the battery is too high, so that the negative electrode typically additionally includes a conductive material. Conventionally, point-type conductive materials such as carbon black have been mainly used, and linear conductive materials are also used to further improve conductivity to improve battery capacity.

The single-walled carbon nanotube is one of the linear conductive materials, and improves conductivity in the negative active material layer based on its elongated shape. Thus, conventionally, a negative electrode slurry was prepared through a dispersion in which the single-walled carbon nanotubes were completely dispersed, and then a negative electrode active material layer was prepared through the negative electrode slurry. However, when the battery is repeatedly charged and discharged, the surface of the single-walled carbon nanotube is damaged or the single-walled carbon nanotube is cut due to excessive volume change of the negative active material, making it difficult to maintain the conductive network in the negative active material layer. there is a problem. Accordingly, the conductive network is blocked or reduced, which degrades the life characteristics of the battery.

Meanwhile, graphene may be used as a planar conductive material. In the case of graphene, there is an advantage of excellent electrical conductivity. However, it is advantageous to form graphene as a single layer to improve conductivity, but the manufacturing cost is increased because the process for manufacturing it in a single layer form is very difficult. Conversely, when graphene has a thickness greater than an appropriate level, there is a problem in that the effect of improving electrical conductivity is insufficient. In addition, even when graphene itself, which has an appropriate level of thickness of 10 nm or less, is used as a conductive material, the performance of the battery is decreased due to the excessive surface contact of the graphene, which prevents it from easily moving to the electrolyte solution and increases the negative electrode resistance. Is lowered. In addition, the graphene has a large surface due to the factors of the method of manufacturing the graphene that is commonly used, and accordingly, the graphene exists while surrounding a large portion of the surface of the negative active material. In that case, since other conductive materials such as carbon nanotubes are mostly aggregated and present on the surface of the graphene rather than directly contacting the negative active material, the entire conductive network of the negative electrode cannot be formed smoothly.

Further, when a silicon-based active material is used as a negative electrode active material, the volume of the silicon-based active material is excessively expanded due to battery charging and discharging, thereby blocking or reducing a conductive path, which degrades the life characteristics of the battery. In the case of the conventional conductive material described above, it is a situation that does not significantly contribute to suppressing blocking or reduction of the conductive path due to volume expansion of the silicon-based active material.

Accordingly, when using a silicon-based active material, a new negative electrode capable of improving the capacity and life of the battery is required.

An object of the present invention is to provide a new negative electrode capable of improving the capacity and life of a battery when using a silicon-based active material, and a secondary battery including the same.

According to an embodiment of the present invention, a negative active material layer is included, the negative active material layer includes a negative active material and a conductive material, the negative active material includes SiO _x (0≦x<2) particles, and the conductive Ashes, secondary particles in which a portion of one graphene sheet is connected to a portion of another graphene sheet adjacent to each other; And a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, wherein the oxygen content of the secondary particles is 1% to 10% by weight based on the total weight of the secondary particles. , The specific surface area of the secondary particles measured by the nitrogen adsorption BET method is 500m ² /g to 1100m ² /g, and the carbon nanotube structure has a negative electrode contained in an amount of 0.01% to 1.0% by weight in the negative active material layer. Is provided.

According to another embodiment of the present invention, a secondary battery including the negative electrode is provided.

According to the present invention, the capacity of the battery may be improved as the negative electrode includes SiO _x (0≦x<2) particles. In addition, since the secondary particles and the carbon nanotube structure introduced in the present invention are used together as a conductive material, the conductivity in the negative active material layer can be greatly improved. Furthermore, based on the rich oxygen content of the secondary particles, the secondary particles may be uniformly dispersed in the cathode. Accordingly, even when the SiO _x (0≦x<2) particles are expanded in volume, a conductive path in the negative electrode is secured, and life characteristics of the battery may be improved.

1 is a schematic diagram and TEM photograph showing a process of forming a graphene sheet contained in secondary particles used in the negative electrode of the present invention.
2 is a TEM and STEM (scanning TEM) photograph of Preparation Example 1 of the present invention.
3 is a SEM photograph of the secondary particles of Preparation Example 1 of the present invention.
4 is a TEM photograph (a) of the secondary particles according to Preparation Example 1 of the present invention and a TEM photograph (b) of the secondary particles according to Preparation Example 2.
5 is a TEM photograph (A) of a carbon nanotube structure included in a negative electrode of an embodiment of the present invention and a TEM photograph (B) of a single-walled carbon nanotube unit according to Preparation Example 5.
6 is an SEM photograph of carbon black of Preparation Example 7 of the present invention.
7 is a SEM photograph of the cathode of Example 1 of the present invention.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention. In this case, the terms or words used in the specification and claims should not be interpreted as being limited to a conventional or dictionary meaning, and the inventor appropriately defines the concept of the term in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

In the present invention, a graphene sheet refers to a carbonaceous structure in the form of a thin film, which includes one or more stacked graphite surfaces and has flexibility.

In the present invention, the lateral size (nm) of the graphene sheet can be evaluated by measuring the size of 100 graphene sheets in the conductive material with TEM (JEOL, JEM-2010F), and an average of these.

In the present invention, the nitrogen adsorption specific surface area (m ² /g) is degassed at 200°C for 8 hours using a BET measuring equipment (BEL-SORP-MAX, Nippon Bell), and N ₂ adsorption at 77K It can be derived by measuring the specific surface area of the target material by proceeding with /desorption/desorption.

In the present invention, the iodine adsorption value (mg/g) can be measured according to the ASTM D1510 method.

In the present invention, the oxygen content (% by weight) is an elemental analysis device (CHN-coder MT-5, Yanako), by measuring the C, H, and N element content, and reflecting the amount of the remaining ash to the oxygen content (Oxygen) ( differential) can be calculated.

In the present invention, the Raman spectrum D/G ratio can be measured by analyzing the Raman spectrum with an Ar-ion laser having a wavelength of 514.5 nm through a Raman spectroscopy equipment (NRS-2000B, Jasco).

<cathode>

A negative electrode according to an embodiment of the present invention includes a negative active material layer, the negative active material layer includes a negative active material and a conductive material, the negative active material includes SiO _x (0≦x<2) particles, The conductive material may include secondary particles in which a portion of one graphene sheet is connected to a portion of another graphene sheet adjacent to each other; And a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, wherein the oxygen content of the secondary particles is 1% to 10% by weight based on the total weight of the secondary particles. , The specific surface area of the secondary particles measured by the nitrogen adsorption BET method is 500m ² /g to 1100m ² /g, and the carbon nanotube structure may be included in an amount of 0.01% to 1.0% by weight in the negative active material layer.

The negative electrode may include a negative active material layer, and more specifically, the negative electrode may include a current collector and a negative active material layer disposed on the current collector. However, the negative electrode does not exclude a so-called “self-supporting negative electrode” in which the negative electrode consists of only a negative electrode active material layer without a current collector.

The current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface-treated aluminum or stainless steel surface with carbon, nickel, titanium, silver, or the like may be used. Specifically, a transition metal that adsorbs carbon well, such as copper and nickel, can be used as the current collector.

The negative active material layer may be disposed on one or both surfaces of the current collector. Of course, in the case of the self-standing negative electrode, the negative active material layer may itself become a negative electrode without a current collector.

The negative active material layer may include a negative active material and a conductive material.

The negative active material may include a silicon-based active material. The silicon-based active material is SiO _x (0≦x<2) particles, Si-C composites and Si-Y alloys (where Y is an alkali metal, alkaline earth metal, transition metal, group 13 element, group 14 element, rare earth element, and these It is an element selected from the group consisting of a combination of) and at least one selected from the group consisting of may be used.

Specifically, the negative active material may include SiO _x (0≦x<2) particles. When the negative active material includes SiO _x (0≦x<2) particles, the capacity of the battery may increase. More specifically, the negative active material may be SiO. In this case, excessive volume expansion of the negative active material during charging and discharging of the battery is controlled, so that the life characteristics of the battery may be improved.

The average particle diameter (D ₅₀ ) of the SiO _x (0≦x<2) particles may be 0.1 μm to 20 μm, and specifically 1 μm to 10 μm. When the above range is satisfied, side reactions between the SiOx and the electrolyte are suppressed, the lithium silicate formation reaction of the SiO _x (0≦x<2) particles is controlled to prevent initial efficiency degradation, and the initial capacity implementation in the negative electrode design Can be maximized.

The negative active material may further include a carbon-based active material. The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, and graphitized mesocarbon microbeads. Specifically, the carbon-based active material is preferably artificial graphite in that it is possible to smoothly control the volume expansion of the negative electrode together with secondary particles (secondary particles included in the conductive material) to be described later.

The weight ratio of the SiO _x (0≦x<2) particles and the carbon-based active material may be 3:97 to 30:70, and specifically 3:97 to 20:80. When the above range is satisfied, excessive volume expansion of the SiO _x (0≦x<2) particles may be suppressed and the capacity of the battery may be improved. In addition, when considering the use of secondary particles (secondary particles included in the conductive material) and carbon nanotube structures to be described later, the weight ratio of the SiO _x (0≤x<2) particles and the carbon-based active material is within the above-described range. It is most preferred.

The conductive material may include secondary particles in which a portion of one graphene sheet is connected to a portion of another graphene sheet adjacent to each other; And a carbon nanotube structure.

(1) secondary particles

The secondary particles may include a structure in which a plurality of graphene sheets are connected. Specifically, at least the secondary particles may have two or more graphene sheets directly connected to each other or indirectly connected to each other.

The secondary particles may have a structure in which a portion of one graphene sheet is connected to a portion of another graphene sheet adjacent to it. More specifically, the plurality of graphene sheets may be connected to each other to form secondary particles in the form of long chains. For example, the chain-shaped secondary particles may partially include a region in which the plurality of graphene sheets are aggregated. Since the secondary particles have a unique chain-shaped connection structure, the secondary particles have excellent electrical and thermal conductivity.

Typical planar graphenes have a two-dimensional arrangement based on a thin thickness compared to the width of the plane. Accordingly, most of the conductive networks formed in the cathode are formed based on the two-dimensional arrangement. On the other hand, the graphene sheets included in the secondary particles include a plurality of graphene sheets having an irregular arrangement. Specifically, the graphene sheets included in the secondary particles include a plurality of graphene sheets having different directions (directions perpendicular to the surface of the graphene sheet). That is, the secondary particles may have a three-dimensional arrangement formed by connecting graphene sheets arranged in various directions to each other. More specifically, since the graphene sheets have the three-dimensional arrangement and have a chain shape arranged to have a predetermined length, a conductive network formed in the cathode may be formed based on the three-dimensional arrangement. . Accordingly, it is possible to form a conductive network in various directions, and since the conductive connection between the carbon nanotube structure and the secondary particles to be described later can be effectively made, the conductivity in the cathode can be greatly improved. In particular, in terms of combination with a carbon nanotube structure to be described later, since the graphene sheets of the secondary particles have various orientations, the carbon nanotube structure connected to the graphene sheet may also exist in the cathode in various directions. . Accordingly, a conductive network in the cathode can be formed more effectively. Here, the graphene sheet may include a plurality of graphene sheets arranged in the same direction with each other, but even in such a case, the graphene sheet also includes a plurality of graphene sheets arranged in different directions.

Meanwhile, as the SiOx (0≦x<2) particles are included in the negative active material, the capacity of the battery may be greatly improved. However, the SiOx (0≦x<2) particles have a lower conductivity than graphite, and there is a problem of deteriorating battery performance due to excessive expansion in volume during charging/discharging of the battery. In this regard, since the conductive material includes the secondary particles, the contact between the negative active material and the secondary particles can be improved, and the carbon nanotube structure is dispersed in various directions by the secondary particles. SiOx (0≦x<2) It is possible to compensate for the problem of decrease in conductivity due to shrinkage/expansion of particles. Furthermore, although the secondary particles are dispersed through an aqueous solvent, the secondary particles may be uniformly dispersed due to the presence of an abundant oxygen functional group in the secondary particles. Accordingly, the problem of decrease in conductivity due to the use of the SiOx (0≤x<2) particles can be greatly improved, and battery performance can be improved by minimizing deterioration in lifespan during charging/discharging of the battery. Moreover, since the secondary particles act as a hub between the carbon nanotube structures, conductivity may be further improved.

The secondary particles may further include a connection part connected to at least some of the graphene sheets among the plurality of graphene sheets. In the present invention, when preparing the secondary particles, conductive particles such as carbon black are ruptured by continuous oxidation to form the graphene sheet, and there may be portions that do not rupture and maintain the original shape. . In this case, a portion maintaining the shape may correspond to the connection portion. Accordingly, the connection portion may have a non-graphene form, and the non-graphene form may mean a lump shape having a thickness greater than that of the graphene sheet unlike the above-described graphene sheet.

A portion of each of the plurality of graphene sheets may be directly connected to each other. Alternatively, at least a portion of the graphene sheets among the plurality of graphene sheets may be connected to each other through the connection part, and specifically, at least a part of each of the plurality of graphene sheets may be connected to the connection part. The conductive material of the present invention may include both of the above two connection methods.

The secondary particles are carbon black in the form of particles close to a sphere, such as acetylene black, furnace black, thermal black, channel black, and lamp black. (lamp black) may be formed by deforming its shape by oxidation treatment. Referring to the schematic diagram of FIG. 1, the structure of carbon black may be deformed by oxidation treatment to form particles including a plurality of graphene sheets. When the carbon black is in the form of secondary particles, a secondary particle form in which particles including the plurality of graphene sheets are aggregated may be formed.

The average thickness of the graphene sheet may be 10 nm or less, specifically 0.34 nm to 10 nm, and more specifically 0.34 nm to 5 nm. When the above range is satisfied, flexibility peculiar to the graphene sheet may be exhibited, and surface contact by the graphene sheet may be improved, so that the electrical conductivity of the secondary particles may be excellent. The graphene sheet may be in a form in which 10 or less graphene layers are stacked.

The lateral size of the graphene sheet may be 300 nm or less, specifically 10 nm to 300 nm, more specifically 10 nm to 100 nm, and, for example, 50 nm to 90 nm. The longest length of the graphene sheet may be controlled according to the degree of heat treatment, and for example, after the oxidation treatment process, a separate heat treatment may be additionally performed in an inert atmosphere to control the longest length of the graphene sheet. When the above range is satisfied, ions in the electrolyte may be smoothly diffused in the cathode. Accordingly, the rapid charging characteristic of the battery can be improved, and the rate-limiting characteristic can also be improved. The longest length of the graphene sheet means the average of the longest lengths of 100 graphene sheets observed through SEM or TEM, where the longest length refers to a line connecting one point in one graphene sheet to another. It represents the longest length assumed.

The longest length of the graphene sheet is much smaller than that of general graphene. Conventionally, in the case of graphene having a large longest length used as a conductive material, since the surface of the negative active material is excessively covered, direct contact between the carbon nanotube structure and the negative active material is hindered. On the other hand, since the graphene sheet of secondary particles used in the present invention has a small and longest length, it does not interfere with direct contact between the carbon nanotube structure and the negative electrode active material, so that the conductive network is smoothly formed compared to the amount of the conductive material applied. , It is effective in reducing the resistance of the negative electrode, and in particular, the resistance to movement of the electrolyte in the negative electrode can be effectively reduced. These characteristics show that the conventional general graphene and the secondary particles introduced in the present invention form a conductive network through a completely different mechanism, which means that they are completely different materials.

The oxygen content of the secondary particles may be 1% by weight or more based on the total weight of the secondary particles, and specifically 1% by weight to 10% by weight. When the above range is satisfied, since the secondary particles can be smoothly dispersed in the negative electrode slurry formed during preparation of the negative electrode, the conductivity of the negative electrode may be improved, and the capacity of the manufactured battery may be improved. The oxygen content may be measured by a method of C, H, O, and N elemental analysis.

The oxygen content may be achieved in the process of oxidizing carbon black. Specifically, an oxygen-containing functional group may be formed on the surface of the secondary particles by the oxidation treatment. The oxygen-containing functional group may be at least one selected from the group consisting of a carboxyl group, a hydroxy group, and a carbonyl group. After the oxidation treatment process, the oxygen content may be additionally controlled through heat treatment of the conductive material in an inert atmosphere.

Since the secondary particles are manufactured by oxidizing carbon black composed of a plurality of primary particles, they have a unique shape including a plurality of graphene sheets generated by rupture of the spherical primary particles. Accordingly, the secondary particles may have carbon black and graphene properties to some extent at the same time, and may have a surface oxygen functional group rich in the secondary particles during the oxidation process. Therefore, the secondary particles can solve the problem of low peelability and hardly dispersing property of conventional graphene based on the characteristics of carbon black, and can maintain high electrical conductivity characteristics of a thin graphene sheet. In addition, when the secondary particles are used together with the carbon nanotube structure, the coagulation phenomenon due to π-π stacking caused by the sp2 carbon surface structure of the same kind by the abundant surface oxygen functional groups of the secondary particles (carbon nanotubes Aggregation of the structure and the secondary particles) can be suppressed, thereby contributing to the dispersibility of the carbon nanotube structure to form a more tightly conductive network in the cathode.

The secondary particles may have a higher degree of graphitization than carbon black before oxidation treatment. Specifically, a high structural stress generated by the surface tension of the carbon black is partially relieved as graphene sheets are formed, so that the graphitization degree of the produced secondary particles may increase.

When measuring the Raman spectrum, the secondary particles may have a D/G peak ratio of 2.0 or less, specifically 0 to 2.0, more specifically 0.9 to 2.0, and, for example, 1.1 to 1.8. In the Raman spectrum, G peak of 1590cm ^-1, near shows a modification resulting from the E _2g mode vibration of the carbon sp ² bond, D peak in the vicinity of 1350cm ^-1 is shown when there is a defect in the sp ² carbon bond. That is, when the D/G peak ratio is satisfied, it means that a high degree of graphitization can be obtained. Accordingly, when the secondary particles are used as a conductive material, the high electrical conductivity of the secondary particles Capacitance and electrical characteristics can be improved.

The secondary particles may have a value calculated by the following Equation 1 of 0.2 or less, specifically 0 to 0.15, and more specifically 0 to 0.1.

[Equation 1]

In Equation 1, a is the specific surface area (m ² /g) of the secondary particles measured by the nitrogen adsorption BET method, and b is the iodine adsorption value (mg/g) of the secondary particles. When the secondary particles have a pore structure inside or between the particles, a large number of small-sized nitrogen (N ₂ ) molecules may be adsorbed in the pores. On the other hand, iodine (I ₂ ), which is a relatively large molecule, is difficult to enter into the pores compared to nitrogen, so that the iodine adsorption value is not large. That is, when there is a void structure, the value according to Equation 1 increases. In other words, in the conductive material of the present invention, a value of 0.2 or less according to Equation 1 means that the secondary particles do not contain micropores or contain a very small amount. That is, when the pores do not exist or exist in a very small amount, since the degree to which iodine is adsorbed and the degree to which nitrogen is adsorbed are similar, the value of Equation 1 becomes smaller. This means that the surface of the secondary particles is a free surface. Specifically, most of the carbon black is transformed into a hollow structure by oxidation treatment, and the structure is destroyed by continuous oxidation treatment, thereby forming graphene sheets. At this time, the graphene sheets may be formed in a shape that opens toward the outside without forming a void structure.

The specific surface area (m ² /g) of the secondary particles measured by the nitrogen adsorption BET method may be 500m ² /g or more, specifically 500m ² /g to 1100m ² /g, and more specifically 500m ² / It may be from g to 900 m ² /g. When the specific surface area range is satisfied, it means that the graphene sheets in the secondary particles exist in various directions, and thus, even if the content of the secondary particles in the anode is small, the conductivity of the anode can be secured.

The secondary particles may be included in an amount of 0.01% to 2.0% by weight in the negative active material layer, specifically 0.05% to 1.5% by weight, and more specifically 0.1% to 1.0% by weight. If the above range is satisfied, the negative electrode adhesion and electrical conductivity can be greatly improved, and the input/output characteristics and life characteristics of the battery can be improved by only applying a small secondary particle content.

(2) carbon nanotube structure

The carbon nanotube structure may include a plurality of single-walled carbon nanotube units. Specifically, the carbon nanotube structure may be a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded side by side with each other, and more specifically, the carbon nanotube structure is 2 to 4,500 single-walled carbons. It may be a carbon nanotube structure in which nanotube units are bonded to each other. More specifically, in consideration of the dispersibility of the carbon nanotube structure and the durability of the cathode, the carbon nanotube structure includes 2 to 50, for example, 15 to 50 single-walled carbon nanotube units bonded to each other. Most preferably, it is a tube structure.

In the carbon nanotube structure, the single-walled carbon nanotube units are arranged and bonded side by side (the long axes of the units are combined in parallel with each other to have a flexible cylindrical structure) to form the carbon nanotube structure. In the negative active material layer, the carbon nanotube structures may be connected to each other to exhibit a network structure.

Conventional cathodes including carbon nanotubes, in conventional cathodes including general carbon nanotubes, are bundled or entangled type carbon nanotubes (single-walled carbon nanotube units or multi-walled A conductive material dispersion is prepared by dispersing the carbon nanotube units (in a form in which the carbon nanotube units are attached or entangled with each other) in a dispersion medium, and then a negative electrode active material layer is prepared using the conductive material dispersion. At this time, the carbon nanotubes are completely dispersed in the conventional conductive material dispersion, and exist as a conductive material dispersion in which single-stranded carbon nanotube units are dispersed. In the conventional conductive material dispersion, the carbon nanotube units are easily cut by an excessive dispersion process to have a shorter length (for example, less than 3 μm) compared to the initial stage, or to be easily cut off. Accordingly, since the single-stranded units cannot properly function as a buffer against pressure, it is difficult to suppress damage (eg, cracking) of the negative electrode active material in the rolling process during battery manufacturing. In addition, since the single-walled carbon nanotube units have a thin diameter and a property of being easily broken, it is difficult to secure a space between the anode active materials, and thus the porosity of the anode active material layer is inevitably low. Accordingly, there is a problem that the diffusion rate of lithium ions decreases. In addition, in the case of the multi-walled carbon nanotube unit, the structure is high due to the mechanism of node growth (not smooth linear, but due to defects occurring in the growth process). Therefore, during the dispersion process, the multi-walled carbon nanotube units are more easily cut, and the multi-walled carbon nanotube units cut short by π-π stacking due to the carbon surface bonding structure (sp2) of the unit aggregate with each other. (aggregation) is easy. Accordingly, it is difficult to exist even more uniformly dispersed in the negative electrode slurry.

In contrast, in the case of the carbon nanotube structure included in the negative active material layer of the present invention, a rope in which 2 to 5,000 single-walled carbon nanotube units maintaining high crystallinity without relatively structural defects are arranged side by side with each other. Since it has a shape (refer to (A) of FIG. 5), it is possible to maintain the length smoothly without being cut even with a change in the volume of the negative active material, so that the conductivity of the negative electrode can be maintained even during the continuous charging/discharging process of the battery. In addition, based on the high electrical conductivity of the single-walled carbon nanotube unit having high crystallinity, the conductivity of the negative electrode is increased to reduce negative electrode resistance, and the energy density, life characteristics, and rapid charging performance of the battery can be greatly improved. In addition, since the carbon nanotube structures are connected to each other in the negative active material layer directly subjected to pressure during rolling to have a network structure, damage to the negative active material (eg, cracking phenomenon such as cracks) may be suppressed. In addition, even if a crack occurs in the negative active material, the carbon nanotube structure crosses the crack and connects the negative active material, thereby maintaining a conductive network. Further, since the carbon nanotube structure is not easily broken and can maintain a long shape, a conductive network can be strengthened over the entire negative active material layer. In addition, desorption of the negative active material may be suppressed, so that adhesion of the negative electrode may be greatly improved.

In the carbon nanotube structure, the average diameter of the single-walled carbon nanotube unit may be 0.5nm to 5nm, specifically 1nm to 5nm. When the average diameter is satisfied, there is an effect of maximizing the conductivity in the negative electrode even with a very small amount of the conductive material. The average diameter corresponds to the average value of the upper 100 single-walled carbon nanotube units and the lower 100 single-walled carbon nanotube units having a larger diameter when observed through TEM.

In the carbon nanotube structure, the average length of the single-walled carbon nanotube unit may be 1 μm to 100 μm, and specifically 5 μm to 50 μm. When the average length is satisfied, a long conductive path for conductive connection between the negative active materials can be formed, and a unique network structure can be formed, so that the conductivity in the negative electrode can be maximized even with a very small amount of conductive material. It works. The average length corresponds to the average value of the upper 100 single-walled carbon nanotube units and the lower 100 single-walled carbon nanotube units having a larger length when observed through TEM.

The specific surface area of the single-walled carbon nanotube unit may be 500m ² /g to 1,000m ² /g, and specifically 600m ² /g to 800m ² /g. When the above range is satisfied, a conductive path in the negative active material layer can be smoothly secured due to a large specific surface area, so that even with a very small amount of conductive material, the conductivity in the negative active material layer can be maximized. The specific surface area of the single-walled carbon nanotube unit may be specifically calculated from the nitrogen gas adsorption amount under liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan.

The average diameter of the carbon nanotube structure may be 2nm to 200nm, specifically 5nm to 150nm, and more specifically 8nm to 20nm. When the above range is satisfied, the carbon nanotube structure is smoothly dispersed to form a conductive network structure, and it is advantageous to connect negative active materials to realize excellent electrical conductivity. The average length corresponds to the average value of the diameters of the upper 100 carbon nanotube structures and the lower 100 carbon nanotube structures having a large average diameter when the prepared negative electrode is observed through SEM.

The average length of the carbon nanotube structure may be 1 μm to 500 μm, specifically 5 μm to 100 μm, and more specifically 6 μm to 20 μm. When the above range is satisfied, it is effective in forming a conductive network structure, and it is advantageous in connecting negative active materials to realize excellent electrical conductivity. The average length corresponds to the average length of the upper 100 carbon nanotube structures and the lower 100 carbon nanotube structures having a large average length when the prepared negative electrode is observed through SEM.

The carbon nanotube structure may be included in an amount of 0.01% to 1.0% by weight in the negative active material layer, specifically 0.01% to 0.5% by weight, and more specifically 0.01% to 0.1% by weight. have. When the above range is satisfied, a conductive path of the negative electrode is secured, so that the battery life characteristics can be improved while maintaining a low level of negative electrode resistance. When preparing the conductive material dispersion, when the bundled carbon nanotubes are completely dispersed (as a general dispersion method, the carbon nanotube units of one strand are dispersed so that they are separated from each other), the carbon nanotube structure does not occur or even if it occurs unintentionally. It occurs in very small amounts (eg 0.0005% by weight). That is, the above content range can never be achieved by a general method. Since the carbon nanotube structure has a form in which 2 to 5,000 single-walled carbon nanotube units are arranged side by side and bonded to each other, the carbon nanotube structure is not cut and the length can be maintained smoothly even when the volume of the negative electrode active material changes. have. Accordingly, the conductivity of the electrode can be maintained, and the conductivity of the cathode can be smoothly secured based on the high conductivity of the single-walled carbon nanotube unit included in the carbon nanotube structure. Accordingly, even if the content of the carbon nanotube structure in the negative electrode is low, the input/output characteristics and life characteristics of the battery may be excellent.

Meanwhile, in some cases, the single-walled carbon nanotube unit included in the carbon nanotube structure may be surface-treated through oxidation treatment or nitriding treatment to improve affinity with a dispersant.

The carbon nanotube structure has the following effects when used in combination with the above-described secondary particles. The secondary particles are mainly disposed on the surface of the negative electrode active material or on the network structure formed by the carbon nanotube structures, and serve as a short conductive network. On the other hand, the carbon nanotube structure builds a relatively long conductive network based on its long length. In addition, as described above, when the battery is charged and discharged, the carbon nanotube structure can maintain its shape more than that of the single-walled carbon nanotube unit (a form dispersed in one strand), so that the conductive network can be maintained more strongly.

The weight ratio of the secondary particles and the carbon nanotube structure may be 100:1 to 100:200, specifically 100:2 to 100:100, and more specifically 100:2 to 100:50. . When satisfying the above range, while increasing the solid content of the negative electrode slurry, it is possible to reduce the total conductive material content for an appropriate level of conductivity. In addition, since the electrical conductivity and adhesion of the negative electrode can be simultaneously improved, input/output characteristics and life characteristics of the battery can be greatly improved.

The conductive material may further include a multi-walled carbon nanotube unit. When the multi-walled carbon nanotube unit is further included, a conductive path can be more smoothly secured, and excessive volume expansion of SiO _x (0≤x<2) particles can be effectively controlled, so that the lifespan characteristics of the battery are reduced. It can be improved. Here, the multi-walled carbon nanotube unit refers to a multi-walled carbon nanotube strand that is completely dispersed and exists in the cathode one by one.

The specific surface area of the multi-walled carbon nanotube unit may be 150 m ² /g to 210 m ² /g, and specifically 170 m ² /g to 190 m ² /g. When the above range is satisfied, the multi-walled carbon nanotube unit is smoothly dispersed in the negative electrode, and there is an effect of smoothly securing a conductive path together with the secondary particles.

The average diameter of the multi-walled carbon nanotube unit may be 7nm to 13nm, specifically 8nm to 12nm, and more specifically 8.5nm to 11.5nm. When the above range is satisfied, a conductive path can be smoothly secured. The average diameter can be derived by observing the prepared negative electrode with an SEM, and obtaining an average value of the diameters of 20 multi-walled carbon nanotube units.

The multi-walled carbon nanotube unit may be included in an amount of 0.01% to 1.0% by weight in the negative active material layer, and specifically 0.01% to 0.07% by weight. When the above range is satisfied, dispersibility and stability of the multi-walled carbon nanotube unit may be enhanced, and a conductive network in the negative electrode may be formed smoothly, and thus input/output characteristics and lifespan characteristics of a battery may be improved.

The negative active material layer may further include carboxy methyl cellulose (CMC). The carboxymethyl cellulose may be a material that begins to be included in the negative electrode from a conductive material dispersion (dispersion of the secondary particles, dispersion of the carbon nanotube structure) required for preparing the negative electrode slurry, and reinforces the role of a binder in preparing the negative electrode slurry. It can also be added to the risk.

The weight average molecular weight of the carboxy methyl cellulose may be 50,000 g/mol to 500,000 g/mol, specifically 50,000 g/mol to 150,000 g/mol, more specifically 90,000 g/mol to 110,000 g/mol. When the above range is satisfied, since the carboxy methyl cellulose can easily penetrate between single-walled carbon nanotube units in the bundled carbon nanotubes, appropriate dispersion of the bundled carbon nanotubes is possible, and the conductive The phase stability of the re-dispersion can be improved. Accordingly, the conductivity of the manufactured negative electrode is greatly improved, and battery performance such as input/output characteristics and lifespan of the battery may be improved.

The degree of substitution of the carboxy methyl cellulose may be 0.1 to 3, and specifically 0.5 to 2. The degree of substitution means the degree to which the hydroxy group of the carboxy methyl cellulose is substituted by the functional group A. The degree of substitution indicates the degree of substitution of the hydroxy group with the functional group A in the molecular structure of carboxymethylcellulose, that is, the degree of substitution of the hydroxy group by the functional group A. Specifically, if one of the three hydroxy groups present in one repeating unit is substituted with the functional group A, the degree of substitution of the repeating unit is 1, and if all three hydroxy groups are substituted with the functional group A, the degree of substitution of the repeating unit is 3 And, if all three hydroxy groups are not substituted, the degree of substitution of the repeating unit is 0. In the carboxymethyl cellulose, the degree of substitution of the hydroxy group by the functional group A represents an average value of the degree of substitution of each repeating unit. In addition, the functional group A may include at least one of -CH ₂ CO ₂ Na and -CH ₂ CO ₂ H.

When the carboxy methyl cellulose has the degree of substitution, the functional groups A can smoothly interact with the single-walled carbon nanotube unit, thereby improving the dispersibility of the carbon nanotube structure. Accordingly, adhesion of the negative electrode may be further improved, and life characteristics of the battery may be improved.

The negative active material layer may further include a binder. The binder is for securing adhesion between negative active materials or between the negative active material and the current collector, and general binders used in the art may be used, and the type is not particularly limited. As the binder, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch , Hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR) , Fluororubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used.

The binder may be included in an amount of 10% by weight or less based on the total weight of the electrode active material layer, and preferably in an amount of 0.1% to 5% by weight. When the content of the binder satisfies the above range, it is possible to implement excellent electrode adhesion while minimizing an increase in electrode resistance.

<Secondary battery>

A secondary battery according to another embodiment of the present invention may include the negative electrode of the above-described embodiment.

Specifically, the secondary battery may include the negative electrode, the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, a detailed description will be omitted.

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

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , Nickel, titanium, silver, or the like may be used. In addition, the positive electrode current collector may generally have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may include a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium iron oxides such as LiFe ₃ O ₄ ; Lithium manganese oxides such as formula Li _1+c1 Mn _2-c1 O ₄ (0≦ _c1 ≦0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Formula LiNi _1-c2 M _c2 O ₂ (here, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3) Ni-site type lithium nickel oxide; Formula LiMn _2-c3 M _c3 O ₂ (wherein, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01≦c3≦0.1) or Li ₂ Mn ₃ MO A lithium manganese composite oxide represented by ₈ (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); Li in the formula may include LiMn ₂ O _{4 in} which a part of Li is substituted with an alkaline earth metal ion, but is not limited thereto. The anode may be Li-metal.

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

In this case, the positive electrode conductive material is used to impart conductivity to the positive electrode, and may be used without particular limitation as long as it does not cause chemical changes and has electronic conductivity in the configured battery. 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 powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, a conductive polymer such as a polyphenylene derivative may be used, and one of them alone or a mixture of two or more may be used.

Further, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC). ), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used.

As a separator, it separates the negative electrode and the positive electrode and provides a passage for lithium ions.If it is used as a separator in a general secondary battery, it can be used without special restrictions.In particular, it has low resistance against the movement of ions of the electrolyte and has excellent electrolytic solution moisture. It is desirable. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A stacked structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used in a single layer or multilayer structure.

The electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used when manufacturing a lithium secondary battery.

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

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dime Oxyethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid tryester, trimethoxy methane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyrofion An aprotic organic solvent such as methyl acid or ethyl propionate may be used.

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

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

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

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and site characteristics, a mid- to large-sized device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems It can be used as a power source.

<Method of manufacturing the cathode>

A method of manufacturing a negative electrode according to another embodiment of the present invention includes: preparing a conductive material; Preparing a negative electrode slurry including a negative electrode active material and the conductive material; And drying the negative electrode slurry to prepare a negative active material layer, wherein the negative active material layer includes a negative active material and a conductive material, and the negative active material includes SiO _x (0≦x<2) particles And, the conductive material, a portion of the graphene sheet is a secondary particle connected to a portion of the adjacent graphene sheet; And a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, wherein the oxygen content of the secondary particles is 1% to 10% by weight based on the total weight of the secondary particles. , The specific surface area of the secondary particles measured by the nitrogen adsorption BET method is 500m ² /g to 1100m ² /g, and the carbon nanotube structure may be included in an amount of 0.01% to 1.0% by weight in the negative active material layer. Specifically, the negative active material, the conductive material, and the negative active material layer are the same as the negative active material, the conductive material, and the negative active material layer described in the above-described embodiment, and thus description thereof will be omitted.

Preparing the conductive material may include preparing the secondary particles and preparing the carbon nanotube structure.

1) Preparation of secondary particles

Preparing the secondary particles may include preparing conductive particles; And deforming the conductive particles by oxidation treatment, wherein the step of modifying the conductive particles by oxidation treatment includes: a) heat treating the conductive particles at a heat treatment temperature of 200°C to 800°C in an oxygen atmosphere or an air atmosphere. It may include at least one of, and b) reacting the conductive particles with an acidic vapor of 120°C to 300°C.

In the step of preparing the conductive particles, the conductive particles may be carbon black. Specifically, the conductive particles may be at least one selected from the group consisting of acetylene black, furnace black, thermal black, channel black, and lamp black. More specifically, the conductive particles may be acetylene black having excellent graphitization degree by being manufactured at the highest temperature.

Preparing the conductive particles may include pyrolyzing acetylene gas, and carbon black, specifically acetylene black, may be formed through the pyrolysis. The acetylene gas may be a high purity acetylene gas, specifically an acetylene gas having a purity of 95% or more, and more specifically, a purity of 98% or more.

The pyrolysis may be to pyrolyze the acetylene gas at a temperature of 1500°C or higher, specifically 1500°C to 2200°C, and more specifically 1500°C to 2000°C. When the above range is satisfied, the graphitization degree of the prepared conductive particles may be high, and the graphitization degree of the prepared secondary particles may also be high. Accordingly, the electrical conductivity of the secondary particles may be improved.

The conductive particles may be carbon black, but among them, acetylene black may be preferable from the following points. The graphene sheet included in the secondary particles may be formed by deforming the surface of the conductive particles by oxidation treatment. Acetylene black formed by the thermal decomposition has a high degree of graphitization of the surface. Therefore, compared to the oxidation treatment of other carbon blacks that inevitably contain some oxygen functional groups on the surface, the structure of the graphene sheet may be smoothly formed when the acetylene black is oxidized.

The pyrolysis may be an instantaneous pyrolysis by adjusting the temperature inside the reaction furnace within the above temperature range, and then introducing an acetylene gas into the reaction furnace. In addition, in this process, air, oxygen, H ₂ O, etc. may be additionally added to control the density of secondary particles and oxygen functional groups, and the connection structure of graphene sheets in the secondary particles may be controlled.

The step of deforming the conductive particles by oxidation treatment includes: a) subjecting the conductive particles to a heat treatment temperature of 200°C to 800°C in an oxygen atmosphere or an air atmosphere (step a); And b) reacting the conductive particles with an acidic vapor of 120° C. to 300° C. (step b).

In step a, the oxygen atmosphere or the air atmosphere may be formed by introducing oxygen or air into a reaction furnace in which the conductive particles are accommodated. Specifically, the graphene sheet structure may be formed by an oxidation process in the reactor according to the setting of an appropriate inflow amount and rate of oxygen or air, a reaction temperature, and a reaction time during the first heat treatment. In addition, the conditions of the oxidation process may vary based on differences in the density of the conductive particles and the content of oxygen functional groups.

In step a, the first heat treatment may be performed by adjusting the temperature of the reaction furnace in the reaction furnace containing the conductive particles. The first heat treatment may be heat treatment at a heat treatment temperature of 200°C to 800°C, and specifically, heat treatment at a heat treatment temperature of 200°C to 450°C. When the temperature range is satisfied, excessively rapid oxidation of the conductive particles may be prevented, and a graphene sheet having a desired size may be formed. The first heat treatment may be performed for 1 to 50 hours.

In step b, the conductive particles may react with acidic vapor to be oxidized to form graphene. Specifically, the acidic vapor may be vapor derived from an acidic solution such as HCl or HNO ₃ . The temperature of the acidic vapor reacting with the conductive particles may be in the range of 120 ℃ to 300 ℃.

After the step of deforming the conductive particles by oxidation treatment, a second heat treatment process in an inert atmosphere may be additionally performed in order to increase the size of the formed graphene sheet. Specifically, the method of manufacturing the conductive material may further include performing a second heat treatment of the oxidized and deformed conductive particles in an inert atmosphere at a temperature of 500° C. or higher after the step of deforming the conductive particles by oxidation treatment. In this case, the inert atmosphere may be formed of any one gas selected from the group consisting of vacuum, helium, argon, and nitrogen. The second heat treatment temperature may be 500°C or higher, specifically 500°C to 2800°C, and more specifically 600°C to 1600°C.

The mechanism by which the secondary particles are formed by the method of manufacturing the secondary particles may be as follows. First, the average size of the spherical primary particles is 50 nm or less, and the spherical to chain carbon black, specifically acetylene black, in which the primary particles share a structure, is subjected to oxidation treatment under specific conditions. In this case, an oxidizing agent such as oxygen or acidic vapor penetrates and an oxidation reaction occurs from defects such as grain boundaries or dislocations in the fine unit structure of the carbon black. When the oxidation treatment is performed for a certain period of time in the temperature range mentioned in the above manufacturing method, the oxidizing agent penetrates into the microstructure inside the carbon black, and oxidation proceeds. At this time, in order to relieve the structural stress of the microstructure inside the primary particles having a radius of curvature larger than the radius of curvature of the surface of the spherical primary particles, an oxidation reaction occurs rapidly inside. Accordingly, internal carbons are oxidized to gases such as CO, CO ₂ , and CH _4, and the primary particles are changed into a hollow type. As the surface structure of the hollow primary particles is destroyed by continuous oxidation treatment, most of the structural stress remaining in the spherical primary particles can be relieved, and graphene sheets appear in this process. Accordingly, the smaller the average size of the primary particles, the carbon black, the smaller the internal density of the particles, and the higher the content of oxygen functional groups inside the primary particles than the surface of the primary particles, the faster the transformation process may be. Further, step a is more preferable than step b in that it can further accelerate the transformation process.

2) Preparation of carbon nanotube structure

The preparation of the carbon nanotube structure may include preparing a mixture solution including a dispersion medium, a dispersant, and a bundled single-walled carbon nanotube (a conjugate or aggregate of single-walled carbon nanotube units) (S1-1); And applying a shear force to the mixed solution to disperse the bundled single-walled carbon nanotubes to form a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are side by side (S1-2). I can.

In the step S1-1, the mixed solution may be prepared by adding a bundled single-walled carbon nanotube and a dispersant to a dispersion medium. The bundled single-walled carbon nanotube is present in a bundle form by combining the above-described single-walled carbon nanotube units, and usually includes two or more, substantially 500 or more, for example, 5,000 or more single-walled carbon nanotube units. do.

The specific surface area of the bundled single-walled carbon nanotubes may be 500m ² /g to 1,000m ² /g, and specifically 600m ² /g to 800m ² /g. When the above range is satisfied, a conductive path in the cathode can be smoothly secured by a large specific surface area, and thus there is an effect of maximizing conductivity in the cathode even with a very small amount of conductive material.

The bundled single-walled carbon nanotubes may be included in an amount of 0.1% to 1.0% by weight in the mixed solution, and specifically, may be included in an amount of 0.2% to 0.5% by weight. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, so that a carbon nanotube structure having an appropriate level may be formed, and dispersion stability may be improved.

Water (H ₂ O) may be used as the dispersion medium.

The dispersant may be at least one of carboxy methyl cellulose (CMC) and polyvinylpyrrolidone (PVP), and preferably carboxy methyl cellulose. The carboxy methyl cellulose is the same as the carboxy methyl cellulose of the other examples described above, and a description thereof will be omitted.

The weight ratio of the bundled carbon nanotubes and the dispersant in the mixed solution may be 1:0.1 to 1:2.5, specifically 1:0.5 to 1:2. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, so that an appropriate level of carbon nanotube structure may be formed, and dispersion stability may be improved.

The solid content in the mixed solution may be 0.1% to 20% by weight, and specifically 1% to 10% by weight. When the above range is satisfied, the bundled single-walled carbon nanotubes are dispersed at an appropriate level, so that an appropriate level of carbon nanotube structure may be formed, and dispersion stability may be improved. In addition, the negative electrode slurry may have a viscosity and elasticity suitable for a negative electrode manufacturing process, and contribute to increasing the solid content of the negative electrode slurry.

In the step S1-2, the process of dispersing the bundled carbon nanotubes in the mixed solution includes a homogenizer, a bead mill, a ball mill, a basket mill, an attraction mill, a universal stirrer, a clear mixer, a spike mill, and TK. It can be performed using a mixing device such as a mixer or ultrasonic sonification equipment. Among them, the beads mill method is preferred in that it can precisely control the diameter and size of the carbon nanotube structure, achieve a uniform distribution of the carbon nanotube structure, and have advantages in terms of cost. .

The bead mill method may be as follows. The mixed solution may be placed in a container including beads, and the container may be rotated to disperse the bundled single-walled carbon nanotubes.

At this time, the conditions under which the bead mill method is performed are as follows.

The average particle diameter of the beads may be 0.5mm to 1.5mm, specifically 0.5mm to 1.0mm. When the above range is satisfied, the diameter and size of the carbon nanotube structure can be appropriately controlled without breaking during the dispersion process, and a dispersion solution having a uniform composition can be prepared.

The rotational speed of the container may be 500RPM to 10,000RPM, specifically 2,000RPM to 6,000RPM. When the above range is satisfied, the diameter and size of the carbon nanotube structure can be appropriately controlled without breaking during the dispersion process, and a dispersion solution having a uniform composition can be prepared.

The time during which the beads mill is performed may be 0.5 to 2 hours, specifically 0.5 to 1.5 hours, and more specifically 0.8 to 1 hour. When the above range is satisfied, the diameter and size of the carbon nanotube structure can be appropriately controlled without breaking during the dispersion process, and a dispersion solution having a uniform composition can be prepared. The bead mill execution time refers to the total time to which the beads mill is applied, and thus, if several bead mill is performed, it means the total time over the several times.

The bead mill conditions are for dispersing the bundled single-walled carbon nanotubes at an appropriate level, specifically except for the case where the bundled single-walled carbon nanotubes are completely dispersed into a single strand of single-walled carbon nanotubes. That is, the bead mill condition is a carbon nanotube structure in which the bundle-type single-walled carbon nanotubes are dispersed at an appropriate level, and 2 to 5,000 single-walled carbon nanotube units are bonded side by side in the prepared conductive material dispersion. It is to form. This can be achieved only when the composition of the mixed liquid, the conditions of the dispersion process (eg, bead mill process) and the like are strictly controlled.

Through the above process, a carbon nanotube structure present in the dispersion may be formed.

In the step of preparing a negative electrode slurry including the negative active material and the conductive material, the negative active material and the conductive material may be added to a solvent and then stirred. In addition, the above-described binder may be added to the solvent. The solvent corresponds to a common solvent used in the industry.

Drying the negative electrode slurry to prepare a negative electrode active material layer may include applying the negative electrode slurry to the current collector and drying it to prepare a negative electrode. Alternatively, it may include a method of applying the negative electrode slurry on a support, drying, and removing the support.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Preparation Example 1: Preparation of secondary particle dispersion

(1) Formation of conductive particles (acetylene black)

An acetylene gas having a purity of 98% was instantaneously injected into a reaction furnace having an internal temperature of 2000° C. and thermally decomposed to form acetylene black.

(2) Preparation of secondary particles

Subsequently, the internal temperature of the reactor in which the acetylene black was accommodated was set to 250° C., and oxidation treatment was performed for 30 hours while introducing oxygen. Through this, secondary particles including a plurality of graphene sheets (including a plurality of graphene sheets having different orientations) having a lateral size of 41 nm are connected to each other with adjacent graphene sheets were obtained. . (See Figs. 2 and 3)

(3) Preparation of dispersion

0.4 parts by weight of the secondary particles and 0.6 parts by weight of carboxy methyl cellulose (CMC) (weight average molecular weight: 100,000 g/mol, degree of substitution: 1.0) were mixed with 99.0 parts by weight of water (H ₂ O) as a solvent, and a mixture (solid content of 1.0) % By weight) was formed. The mixture was stirred in a bead-mill manner. At this time, the particle diameter of the beads was 1 mm, and the rotation speed of the stirring vessel containing the beads was 3,000 RPM. The stirring was carried out for 60 minutes.

Preparation Example 2: Preparation of secondary particle dispersion

For the conductive material obtained in Preparation Example 1, additional heat treatment was performed at 900°C for 1 hour in an inert atmosphere, and a plurality of graphene sheets having a lateral size of 65 nm level were connected to each other with adjacent graphene sheets. To obtain secondary particles containing. Referring to FIG. 4, it can be seen that the conductive material of Preparation Example 1 shown in FIG. 4A was transformed into the conductive material of Preparation Example 2 of FIG. 4B by heat treatment. Specifically, it can be seen that adjacent graphene sheets are interconnected by the heat treatment to increase the maximum length.

Thereafter, a dispersion of secondary particles was prepared under the same stirring conditions as in Preparation Example 1.

Preparation Example 3: Preparation of carbon nanotube structure

Bundled single-walled carbon nanotubes consisting of single-walled carbon nanotube units with an average diameter of 1.5 nm and an average length of 5 μm or more (specific surface area 650 m ² /g) 0.4 parts by weight and carboxy methyl cellulose (CMC) (weight average molecular weight : 100,000 g/mol, degree of substitution: 1.0) 0.6 parts by weight of water (H ₂ O) as a solvent was mixed with 99.0 parts by weight, and a mixture was prepared so that the solid content was 1.0% by weight.

The mixture was stirred in a bead-mill method to disperse the bundled single-walled carbon nanotubes in a solvent to prepare a carbon nanotube structure dispersion. At this time, the particle diameter of the beads was 1 mm, and the rotation speed of the stirring vessel containing the beads was 3,000 RPM. The stirring was carried out for 60 minutes. The carbon nanotube structure dispersion liquid contained a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units were bonded side by side (see FIG. 5A).

In the dispersion of the carbon nanotube structure, the carbon nanotube structure was 0.4% by weight and the carboxy methyl cellulose was 0.6% by weight.

Preparation Example 4: Preparation of carbon nanotube structure

Except that the carboxy methyl cellulose used in Preparation Example 3 was modified with carboxy methyl cellulose having a weight average molecular weight of 400,000 g/mol and a degree of substitution of 1.0, a carbon nanotube structure dispersion was prepared in the same manner as in Preparation Example 3 Was prepared.

Preparation Example 5: Preparation of single-walled carbon nanotube unit

In Preparation Example 3, carboxy methyl cellulose was modified to 1.2 parts by weight, and stirring through a bead mill was performed for 60 minutes as 1 cycle, except that a total of 4 cycles (natural cooling performed for 60 minutes between each cycle) was performed. Then, a single-walled carbon nanotube unit dispersion was prepared through the same method as in Preparation Example 3 (see FIG. 5B). In the dispersion, the bundle-type single-walled carbon nanotubes were completely dispersed, so that the single-walled carbon nanotubes were present in a single strand unit, but the above-described carbon nanotubes structure was not detected.

Preparation Example 6: Preparation of multi-walled carbon nanotube monomer dispersion

Bundled multi-walled carbon nanotubes (specific surface area 184m ² /g, the average diameter of the multi-walled carbon nanotube units included is 10 nm) 0.4 parts by weight and carboxy methyl cellulose (CMC) (weight average molecular weight: 100,000 g/ mol, degree of substitution: 1.0) 0.6 parts by weight of water (H ₂ O) as a solvent was mixed with 99.0 parts by weight to form a mixture. The mixture was stirred in a bead-mill manner. At this time, the particle diameter of the beads was 1 mm, and the rotation speed of the stirring vessel containing the beads was 3,000 RPM. The stirring was carried out for 60 minutes.

Preparation Example 7: Preparation of carbon black dispersion

0.4 parts by weight of carbon black (secondary particle form with a specific surface area of 135 m ² /g and a primary particle diameter of 23 nm) and carboxy methyl cellulose (CMC) (weight average molecular weight: 100,000 g/mol, degree of substitution: 1.0) 0.6 parts by weight of water (H ₂ O) was mixed with 99.0 parts by weight of a solvent to form a mixture. The mixture was stirred in a bead-mill manner. At this time, the particle diameter of the beads was 1 mm, and the rotation speed of the stirring vessel containing the beads was 3,000 RPM. The stirring was carried out for 60 minutes (see Fig. 6).

Example 1: Preparation of negative electrode

Negative active material particles (SiO having an average particle diameter (D ₅₀ ) of 6.6 μm, artificial graphite having an average particle diameter (D ₅₀ ) of 21 μm), styrene butadiene rubber (SBR) and carboxymethylcellulose (CMC) as binders, Preparation Example 1 A negative electrode slurry containing the dispersion of the secondary particles and the dispersion of the carbon nanotube structure of Preparation Example 3 was prepared (solvent: H ₂ O). The weight ratio of the negative active material particles, the binder, the secondary particles, and the carbon nanotube structure was 95.5:3.5:0.95:0.05. The weight ratio of SiO and the artificial graphite was 5:95, and the weight ratio of SBR and CMC of the binder was 2:1.5.

Each of the negative electrode slurries was coated and dried on a copper (Cu) metal thin film of a negative electrode current collector having a thickness of 20 μm at a loading of 160 mg/25 cm ² . At this time, the temperature of the circulating air was 70°C. Subsequently, the negative electrode current collector coated and dried with the slurry was rolled and dried in a vacuum oven at 130° C. for 8 hours to prepare a negative electrode.

Referring to FIG. 7, in the cathode of Example 1, it can be seen that the carbon nanotube structure (a structure in which 2 to 5,000 single-walled carbon nanotube units are arranged side by side and bonded) are connected to each other to form a network structure. . In addition, it can be seen that the secondary particles are disposed on the carbon nanotube structure, so that a strong conductive network is formed by the carbon nanotube structure and the secondary particles.

Example 2: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the secondary particle dispersion of Preparation Example 2 was used instead of the secondary particle dispersion of Preparation Example 1.

Example 3: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the carbon nanotube structure of Preparation Example 4 was used instead of the carbon nanotube structure of Preparation Example 3. The weight ratio of the negative active material particles, the binder, the secondary particles, and the carbon nanotube structure was 95.54:3.46:0.95:0.05. The weight ratio of SiO and the artificial graphite was 5:95, and the weight ratio of SBR and CMC of the binder was 2:1.46.

Example 4: Preparation of negative electrode

Example 1, except that the secondary particle dispersion of Preparation Example 2 was used instead of the secondary particle dispersion of Preparation Example 1, and the carbon nanotube structure dispersion of Preparation 4 was used instead of the carbon nanotube structure dispersion of Preparation Example 3 A negative electrode was prepared in the same manner as described above.

Example 5: Preparation of negative electrode

A negative electrode in the same manner as in Example 1, except that not only the dispersion of the secondary particles of Preparation Example 1 and the dispersion of the carbon nanotube structure of Preparation Example 3 were used, but the multi-walled carbon nanotube unit dispersion of Preparation Example 6 was used together. Was prepared. The weight ratio of the negative active material particle, the binder, the secondary particle, the carbon nanotube structure, and the multi-walled carbon nanotube unit was 95.5:3.5:0.9:0.05:0.05.

Comparative Example 1: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the carbon nanotube structure dispersion of Preparation Example 3 was not used and only the secondary particle dispersion of Preparation Example 1 was used. The weight ratio of the negative active material particles, the binder, and the secondary particles was 95.5:3.5:1.0. The weight ratio of the SiO and the artificial graphite was 5:95, and the weight ratio of the SBR and CMC was 2:1.5.

Comparative Example 2: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the secondary particle dispersion of Preparation Example 2 was used instead of the secondary particle dispersion of Preparation Example 1.

Comparative Example 3: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the multi-walled carbon nanotube unit dispersion liquid of Preparation Example 6 was used instead of the carbon nanotube structure dispersion liquid of Preparation Example 3. The weight ratio of the negative active material particle, the binder, the secondary particle, and the multi-walled carbon nanotube unit was 95.5:3.5:0.95:0.05. The weight ratio of SiO and the artificial graphite was 5:95, and the weight ratio of SBR and CMC of the binder was 2:1.5.

Comparative Example 4: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the secondary particles of Preparation Example 1 were not used and only the carbon nanotube structure of Preparation Example 3 was used.

Comparative Example 5: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the carbon black dispersion of Preparation Example 7 was used instead of the secondary particles of Preparation Example 1. The weight ratio of the negative active material particles, the binder, the carbon black, and the carbon nanotube structure was 95.5:3.5:0.95:0.05. The weight ratio of SiO and the artificial graphite was 5:95, and the weight ratio of SBR and CMC of the binder was 2:1.5.

Comparative Example 6: Preparation of negative electrode

A negative electrode was manufactured in the same manner as in Example 1, except that the single-walled carbon nanotube unit dispersion of Preparation Example 5 was used instead of the carbon nanotube structure of Preparation Example 3. The weight ratio of the negative active material particle, the binder, the secondary particle, and the single-walled carbon nanotube unit was 95.42:3.58:0.95:0.05. The weight ratio of SiO and the artificial graphite was 5:95, and the weight ratio of SBR and CMC of the binder was 2:1.58.

Secondary particle content (% by weight) Carbon nanotube structure content (% by weight) Single-walled carbon nanotube unit (fully dispersed form) content (% by weight) Carbon black content (% by weight) Content of multi-walled carbon nanotube unit (% by weight) Example 1 0.95 0.05 - - - Example 2 0.95 0.05 - - - Example 3 0.95 0.05 - - - Example 4 0.95 0.05 - - - Example 5 0.9 0.05 - - 0.05 Comparative Example 1 1.0 - - - - Comparative Example 2 1.0 - - - Comparative Example 3 0.95 - - - 0.05 Comparative Example 4 - 1.0 - - - Comparative Example 5 - 0.05 - 0.95 - Comparative Example 6 0.95 - 0.05 - -

In Tables 2 and 3, the physical properties of the conductive materials used in Examples and Comparative Examples are shown.

Longest length of graphene sheet or average size of primary carbon black particles (nm) Nitrogen adsorption specific surface area (m ² /g) Iodine adsorption value (mg/g) Oxygen content (% by weight) Raman spectrum D/G ratio Secondary Particles of Preparation Example 1 41 (graphene sheet) 825 849 8.9 1.42 Secondary Particles of Preparation Example 2 65 (graphene sheet) 712 736 3.2 1.27 Carbon black of Preparation Example 7 23 (Carbon black primary particles) 135 152 0.3 1.23 Multi-walled carbon nanotube unit of Preparation Example 6 - 184 - 0.2 0.91

1) Longest length of graphene sheet (lateral size) (nm): After measuring the size of 100 graphene sheets in secondary particles by TEM (JEOL, JEM-2010F), the average of these sheets was evaluated. 2) Nitrogen adsorption specific surface area (m ² /g): Using a BET measuring equipment (BEL-SORP-MAX, Nippon Bell), degassing at 200°C for 8 hours, and N ₂ adsorption/desorption at 77K ( absorption/desorption).

3) Iodine adsorption value (mg/g): It was measured according to ASTM D1510 method.

4) Oxygen content (% by weight): Using elemental analysis equipment (CHN-coder MT-5, Yanako), the content of C, H, and N elements is measured, and oxygen content (differential ) Was calculated.

5) Raman spectrum D/G ratio: Raman spectrum was analyzed and measured with an Ar-ion laser having a wavelength of 514.5 nm through a Raman spectroscopy equipment (NRS-2000B, Jasco).

Average diameter (nm) Average length (㎛) Carbon nanotube structure of Preparation Example 3 1 10.5 8.2 Carbon nanotube structure of Preparation Example 4 101.2 15.6 Single-walled carbon nanotube unit of Preparation Example 5 1.6 1.8 Multi-walled carbon nanotube unit of Preparation Example 6 10.8 1.3

The average diameter and average length are the top 100 carbon nanotube structures (or single-walled carbon nanotube units, or multi-walled carbon nanotube units) having a large diameter (or length) when the prepared cathode is observed through TEM. It corresponds to the average value of the lower 100 carbon nanotube structures (or single-walled carbon nanotube units, or multi-walled carbon nanotube units).

Experimental Example 1: Evaluation of high-temperature life characteristics (capacity retention) of a battery

Using the negative electrodes of Examples 1 to 5 and Comparative Examples 1 to 6, batteries were manufactured as follows, respectively.

Li[Ni _0.6 Mn _0.2 Co _0.2 ]O ₂ was used as a positive electrode active material. The positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a solvent N-methyl-2 pyrrolidone in a weight ratio of 94:4:2 to prepare a positive electrode slurry.

The prepared positive electrode slurry was coated and dried on an aluminum metal thin film that is a positive electrode current collector having a thickness of 15 μm. At this time, the temperature of the circulating air was 110°C. Then, it was rolled and dried in a vacuum oven at 130° C. for 2 hours to form a positive electrode active material layer.

Each of the negative electrodes of Examples 1 to 5 and Comparative Examples 1 to 6, and the prepared positive electrode and porous polyethylene separator were assembled using a stacking method, and an electrolyte solution (ethylene carbonate (EC)/ethyl methyl carbonate (EMC) = 1/2 (volume ratio), lithium hexafluorophosphate (LiPF ₆ 1 mol) was injected to prepare a lithium secondary battery.

Each lithium secondary battery was charged and discharged under the following conditions.

Charging condition: 0.5C constant current charging to 4.25V, then charging at 4.2V until 0.1C current rate flows

Discharge condition: Discharge at 0.5C current rate up to 2.8V

When the above charging and discharging were performed as one cycle, 100 cycles were performed at 45°C. Thereafter, the discharge capacity (capacity retention rate) after 100 cycles was evaluated based on 100% of the discharge capacity after one cycle, and is shown in Table 4.

Capacity retention rate (%) Example 1 94.8 Example 2 95.2 Example 3 93.5 Example 4 94.3 Example 5 95.7 Comparative Example 1 88.3 Comparative Example 2 89.6 Comparative Example 3 91.4 Comparative Example 4 93.1 Comparative Example 5 87.2 Comparative Example 6 88.5

Claims (24)

Including a negative active material layer,
The negative active material layer includes a negative active material and a conductive material,
The negative active material includes SiO _x (0≦x<2) particles,
The conductive material,
Secondary particles in which a portion of one graphene sheet is connected to a portion of another graphene sheet adjacent to each other; And
Including; carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other,
The oxygen content of the secondary particles is 1% to 10% by weight based on the total weight of the secondary particles,
The specific surface area of the secondary particles measured by nitrogen adsorption BET method is 500m ² /g to 1100m ² /g,
The negative electrode included in the carbon nanotube structure in an amount of 0.01% to 1.0% by weight in the negative active material layer.
The method according to claim 1,
The secondary particles, the negative electrode having a structure in which the graphene sheets are connected to each other to show a chain shape.
The method according to claim 1,
The maximum length of the graphene sheet is 10nm to 300nm negative electrode.
The method according to claim 1,
The secondary particle is a negative electrode having a value of 0 to 0.2 calculated by the following Equation 1:
[Equation 1]

In Equation 1, a is the specific surface area (m ² /g) of the secondary particles measured by the nitrogen adsorption BET method, and b is the iodine adsorption value (mg/g) of the secondary particles.
The method according to claim 1,
The secondary particles further include a connection part connected to at least some of the graphene sheets among the plurality of graphene sheets,
The connection part is a negative electrode in a non-graphene form.
The method of claim 5,
At least a portion of each of the plurality of graphene sheets is connected to the connector.
The method according to claim 1,
The negative electrode having an average thickness of the graphene sheet is 0.34nm to 10nm.
The method according to claim 1,
A negative electrode having a D/G peak ratio of 0.9 to 2.0 when a Raman spectrum is measured for the secondary particles.
The method according to claim 1,
In the cathode, the carbon nanotube structures are connected to each other to show a network structure.
The method according to claim 1,
In the carbon nanotube structure,
A negative electrode in which the single-walled carbon nanotube units are arranged and bonded side by side.
The method according to claim 1,
The average length of the carbon nanotube structure is 1㎛ to 500㎛ cathode.
The method according to claim 1,
The average length of the carbon nanotube structure is 8㎛ to 20㎛ cathode.
The method according to claim 1,
The average diameter of the carbon nanotube structure is 2nm to 200nm cathode.
The method according to claim 1,
The carbon nanotube structure is a carbon nanotube structure in which 15 to 50 single-walled carbon nanotube units are bonded to each other.
The method according to claim 1,
A negative electrode having a weight ratio of the secondary particles and the carbon nanotube structure of 100:1 to 100:200.
The method according to claim 1,
The SiO _x (0≦x<2) particles have an average particle diameter (D ₅₀ ) of 0.1 μm to 20 μm.
The method according to claim 1,
The negative active material further comprises a carbon-based active material.
The method according to claim 1,
The negative active material layer further comprises carboxy methyl cellulose.
The method of claim 18,
The weight average molecular weight of the carboxy methyl cellulose is 50,000g / mol to 500,000g / mol of negative electrode.
The method of claim 18,
The degree of substitution of the carboxy methyl cellulose is 0.1 to 3 negative electrode.
The method according to claim 1,
The conductive material is a negative electrode further comprising a multi-walled carbon nanotube unit.
The method of claim 21,
The negative electrode contained in the multi-walled carbon nanotube unit is 0.01% to 1.0% by weight in the negative active material layer.
The method of claim 21,
The average diameter of the multi-walled carbon nanotube unit is 7nm to 13nm cathode.
A secondary battery comprising the negative electrode of claim 1.

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