KR102648840B1 - Composite anode material structure and anode active material for lithium secondary batteries including the same - Google Patents

Abstract

One embodiment of the present invention includes an external pitch coating layer, and the cross section including the center includes a graphene layer; A carbon nanotube layer located on the graphene layer and including a plurality of carbon nanotubes; and a nano silicon particle layer located on the graphene layer and including a plurality of nano silicon particles bonded to the carbon nanotubes. It provides a silicon-graphene-carbon nanotube composite comprising a. Through the production of a silicon-graphene-carbon nanotube composite, optimal charge/discharge capacity and initial efficiency of a lithium secondary battery can be achieved and cycle characteristics can be improved by using a negative electrode active material.

Description

Composite anode material structure and anode active material for lithium secondary batteries including the same}

The present invention relates to a composite negative electrode material structure and a negative electrode active material for lithium secondary batteries containing the same. More specifically, it relates to a silicon-graphene-carbon nanotube composite as a composite negative electrode material and a negative electrode active material for lithium secondary batteries containing the same.

As the size of the portable electronic device and electric vehicle markets expands, research on secondary batteries that can be charged and discharged is actively underway. Among various types of secondary batteries, lithium secondary batteries have a positive electrode formed with a positive electrode active material layer, a negative electrode formed with a negative electrode active material layer, and a separator that electrically insulates between the positive electrode and the negative electrode. Only when the conductive agent particles are well dispersed in the electrode active material slurry can the ionic conductivity of the electrode active material layer be maintained uniformly.

However, when using a typical dispersion method, it is difficult for the conductive agent particles to be uniformly dispersed in the slurry due to differences in particle size and specific gravity between the electrode active material particles and the conductive agent, which leads to a decrease in electrochemical charge and discharge characteristics. Stability and long-term reliability also decrease.

Even if the silicon particles are well dispersed on the graphite, there is some non-uniformity, and the particle shape is difficult to spheroid due to the presence of silicon particles on the expanded expanded graphite, so there are problems in directly applying it as a negative electrode active material. It was revealed through

Accordingly, there was a need to improve uniformity through dispersion. In the case of silicon-graphene composites dispersed using existing dispersion methods, silicon particles and graphene have a randomly overlapping structure, making it difficult to control thickness and particle size, and silicon particles Some agglomeration occurs, resulting in a decrease in charge/discharge characteristics and initial efficiency when electrochemically evaluated, as well as insufficient long-term reliability, and there is a problem of silicon cracking or detachment due to expansion and contraction of silicon during charge and discharge.

KR 10-2010-0006409 A

The technical problem to be achieved by the present invention is the structure of a silicon-graphene-carbon nanotube composite that can improve the charge/discharge capacity and initial efficiency of lithium secondary batteries and manufacture an optimal anode active material to realize cycle characteristics. is to provide.

The technical problem to be achieved by the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description below. There will be.

In order to achieve the above technical problem, one embodiment of the present invention includes an external pitch coating layer, and the cross section including the center includes a graphene layer; A carbon nanotube layer located on the graphene layer and including a plurality of carbon nanotubes; and a nano silicon particle layer located on the graphene layer and including a plurality of nano silicon particles bonded to the carbon nanotubes. It provides a silicon-graphene-carbon nanotube composite comprising a.

In an embodiment of the present invention, the thickness of the graphene layer may be 1 nm to 300 nm.

In an embodiment of the present invention, the length of the carbon nanotube is 0.1 to 30 um, the specific surface area is 100 to 500 m ² /g, the bulk density is 0.05 to 0.2 g/cm ³ , the purity is 95% or more, and a single It may be characterized as a single wall or a multi-layer wall.

In an embodiment of the present invention, the pitch coating layer may have a thickness of 0.05 to 1 μm.

In an embodiment of the present invention, the content of nano silicon may be greater than 0 and less than or equal to 85 wt%.

In order to achieve the above technical problem, another embodiment of the present invention includes preparing a silicon-graphite-carbon nanotube fusion precursor; Plasma processing the silicon-graphite-carbon nanotube fusion precursor; forming an exfoliated silicon-graphene-carbon nanotube composite by dispersing the plasma-treated silicon-graphite-carbon nanotube fusion precursor through a wet grinding process; Coating the peeled silicon-graphene-carbon nanotube composite with a binder; And granulating the binder-coated exfoliated silicon-graphene-carbon nanotube composite to produce a granulated silicon-graphene-carbon nanotube composite. Silicon-graphene comprising a. -Provides a method for manufacturing carbon nanotube composites.

In an embodiment of the present invention, the binder coating may be characterized by coating pitch liquid.

In an embodiment of the present invention, the solvent used in the wet grinding process may be characterized as having a Hansen Solubility Parameter of 17 to 23 MPa ½ or 45 to 50 MPa ½.

In an embodiment of the present invention, the solvent used in the wet grinding process may have a boiling point of 60 to 160°C.

In order to achieve the above technical problem, another embodiment of the present invention provides a negative electrode active material for a lithium secondary battery including the silicon-graphene-carbon nanotube composite.

According to an embodiment of the present invention, the optimal charge/discharge capacity and initial efficiency of a lithium secondary battery can be achieved using a negative electrode active material through the production of a silicon-graphene-carbon nanotube composite, and cycle characteristics can be improved. can do.

The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

Figure 1 is a schematic diagram of the cross section of a silicon-graphene-carbon nanotube composite.
Figure 2 is a schematic diagram according to the configuration of (a) silicon-carbon nanotube, (b) silicon-graphene, and (c) silicon-graphene-carbon nanotube fusion precursor.
Figure 3 is a schematic diagram of a silicon-graphene-carbon nanotube composite.
Figure 4 is an FE-SEM image of a cross section of a silicon-graphene-carbon nanotube composite.
Figure 5 is a graph of electrochemical evaluation of (a) Comparative Example and (b) Example.
Figure 6 is a cycle retention graph of comparative examples and examples.

Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention may be implemented in various different forms and, therefore, is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, combined)" with another part, this means not only "directly connected" but also "indirectly connected" with another member in between. "Includes cases where it is. Additionally, when a part is said to “include” a certain component, this does not mean that other components are excluded, but that other components can be added, unless specifically stated to the contrary.

The terms used herein are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

Terms used in this specification are defined as follows.

“Composite cathode material” refers to a silicon-graphene-carbon nanotube composite.

Figure 1 is a schematic diagram of the cross section of a silicon-graphene-carbon nanotube composite.

Figure 2 is a schematic diagram according to the configuration of (a) silicon-carbon nanotube, (b) silicon-graphene, and (c) silicon-graphene-carbon nanotube fusion precursor.

Figure 3 is a schematic diagram of a silicon-graphene-carbon nanotube composite.

A silicon-graphene-carbon nanotube composite according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

The silicon-graphene-carbon nanotube composite according to an embodiment of the present invention includes an external pitch coating layer, and the cross section including the center includes a graphene layer; A carbon nanotube layer located on the graphene layer and including a plurality of carbon nanotubes; and a nano-silicon particle layer located on the graphene layer and including a plurality of nano-silicon particles bonded to the carbon nanotubes.

The thickness of the graphene layer may be 1 nm to 300 nm. If the thickness is more than 300 nm, some nano-Si agglomerates and grows coarse grains rather than evenly dispersing nano-Si, resulting in increased expansion during electrochemical evaluation of the final composite, which has a negative impact on long-term reliability during electrochemical evaluation.

Carbon nanotubes have a length of 0.1 to 30 μm, a specific surface area of 100 to 500 m ² /g, a bulk density of 0.05 to 0.2 g/cm ³ , a purity of 95% or more, and a single wall or multi-layer wall ( It can be multi wall). If the length of the carbon nanotube is less than 0.1um, entanglements between nano Si and adjacent nano Si may not be achieved, so detachment of nano Si cannot be prevented during electrochemical evaluation of the final composite, and graphene-graphene interlayer conduction may not be achieved. Network formation has also become difficult, and an appropriate range of sizes is required for carbon nanotubes. When using carbon nanotubes longer than 30 um, the effect decreases rapidly due to self-entanglement becoming larger than the optimal entanglement, so a length of 30 um or less is appropriate. In the case of single-wall and multi-layer walls, single-wall has excellent performance, but multi-wall carbon nanotubes, which have the inherent high conductivity of carbon nanotubes, can also be applied.

While the specific surface area of expanded graphite is 10 to 100 m ² /g, carbon nanotubes have a higher specific surface area value of 100 to 500 m ² /g, which is higher than that of expanded graphite, increasing the number of condensation sites for Si, resulting in nano nanoscale up to 85 wt% of Si. Condensation into Si is possible.

The thickness of the pitch coating layer may be 0.05 to 1 μm.

The content of nano silicon may be greater than 0 and less than or equal to 85 wt%. When Si is mixed higher than 85 wt%, rather than condensing into nano-silicon due to excessive Si, growth between nano-Si occurs in large quantities in the fusion precursor, greatly increasing the possibility of μm-level Si being formed.

Hereinafter, a method for manufacturing a silicon-graphene-carbon nanotube composite according to another embodiment of the present invention will be described.

A method for manufacturing a silicon-graphene-carbon nanotube composite according to an embodiment of the present invention includes preparing a silicon-graphite-carbon nanotube fusion precursor; Plasma processing the silicon-graphite-carbon nanotube fusion precursor; forming an exfoliated silicon-graphene-carbon nanotube composite by dispersing the plasma-treated silicon-graphite-carbon nanotube fusion precursor through a wet grinding process; Coating the peeled silicon-graphene-carbon nanotube composite with a binder; and granulating the binder-coated, exfoliated silicon-graphene-carbon nanotube composite to produce a granulated silicon-graphene-carbon nanotube composite.

The first step is to prepare the silicon-graphite-carbon nanotube fusion precursor. Silicon can be μm-level amorphous Si or submicron-level silicon sludge, which is a by-product of solar cell ingot manufacturing. Graphite can be expanded graphite obtained by intercalating flaked graphite with a strong acid. Si-expanded graphite mixed powder can be made by mixing 0 to 85 wt% of Si powder, 99.9 to 15 wt% of expanded graphite, and 20 to 0 wt% of carbon nanotubes using a mixer. The silicon content is greater than 0 and 85 wt% or less, and the silicon content may be a fusion precursor alone, a mixture of a fusion precursor and silicon, or a composite of expanded graphite, carbon nanotubes, and silicon. Here, the specific surface area of expanded graphite is 10 to 100 m ² /g, but in the case of carbon nanotubes, it has a higher specific surface area value of 100 to 500 m ² /g, which is higher than that of expanded graphite, and the number of condensation sites for Si increases, resulting in nano nanoscale up to 85 wt% of Si. Condensation into Si is possible. If Si is mixed higher than 85wt%, rather than condensing into nano-silicon due to excessive Si, growth between nano-Si occurs in large quantities in the fusion precursor, greatly increasing the possibility of μm-level Si being formed.

Here, in the case of carbon nanotubes used in manufacturing the fusion precursor, they are single wall or multi wall, and the main physical properties are bulk density of 0.05 to 0.2 g/cm ³ and specific surface area. Materials with a purity of 100 to 500 m ² /g and over 95% were used.

Next is the step of plasma processing the silicon-graphite-carbon nanotube fusion precursor.

In the step of plasma treating the silicon-graphite-carbon nanotube fusion precursor, N ₂ purge at 20 kW and DC plasma treatment are performed to generate vaporization of Si, and at the same time, as the expanded graphite expands, the expanded graphite layer is expanded between the layers and the carbon nanotube. Nano-sized Si is condensed on the surface of the bundle, ultimately yielding a fusion precursor combining plasma-treated silicon, graphite, and carbon nanotubes.

The next step is to disperse the plasma-treated silicon-graphite-carbon nanotube fusion precursor through a wet grinding process to form an exfoliated silicon-graphene-carbon nanotube composite.

The grinding process may be characterized as a wet grinding process. When dispersing the silicon-graphite fusion precursor using the existing dry grinding process, the exfoliation state of the graphite (platelet graphite/graphene) is not uniform, making it difficult to control the thickness and particle size, and agglomeration of silicon particles occurs, creating problems during electrochemical evaluation. Discharge characteristics and initial efficiency may decrease and long-term reliability may become insufficient.

The solvent used in the wet grinding process may be a single component among aqueous and organic solvents or a combination of miscible solvents. Alcohols including water, ethanol, isopropanol, N-butanol amyl alcohol, cyclohexanol, etc., ketones such as acetone, MEK, MIBK, cyclohexanone, ethyl acetate, isopropanol acetate, N-butyl acetate, amyl acetate, etc. Ester series containing, mineral spirit, heptane, cyclohexane, toluene, hydrocarbon series containing xylene, butyl cellosolve, ethyl cellosolve, etc. cellosolve), acetate, butyl carbitol, glycoether acetate series including butyl carbitol acetate, 1.1.1-trichloroethane (1.1.1-TCE), Halogenated hydrocarbons including TCE and EDC (1,2-dichloroethane), furans including tetrahydrofuran, NMP (N-Methyl-2-pyrrolidone), etc. Solvents containing Lactam-based solvents may be used.

As conditions for the optimal solvent, the boiling point is preferably between 60 and 160°C, and the solvent's Hansen Solubility Parameter (MPa)　 ^½ ) is preferably between 17 and 23 or between 45 and 50. More preferably, it may be between 18 and 22 or between 47 and 48.

Solvents that satisfy this requirement include Acetaldoxime, Acetic acid, Acetic anhydride, Acetonecyanhydrin, N-Acetyl caprolactam, Acetylacetone, Acetylbromide, Allyl acetate, Arryl acetoacetate, Allyl Alcohol, Amyl acetate, Benzene, N-benzyl pyrrolidone, 4-bromo-1-butene. , 1-butanethiol, 2-buanol, 1-butene, Carbon tetrachl oride, Chloro acetaldehyde, Cyclohexanone, Cyclohexanol, 2-chloro allyl alcohol, 4-chloro-1,2-butadiene, 1-chloro-2-butene, Ethanol, These solvents are Isoamyl acetate, Methyl ethyl ketone, Isoamyl alcohol, Xylene, Tetrahydrofuran, Toluene, and Water. It is preferable to use these solvents alone or in combination.

The Hansen Solubility Parameter is a unique value for each solvent developed by Charles M. Hansen in 1966, and can be composed of three parameters: a dispersion force component, a hydrogen bond component, and a terminal polarity component. At this time, the Total Solubility Parameter can be calculated as follows:

HANSEN SOLUBILITY PARAMETERS (HSP)

d ² = dD ² + dP ² + dH ²

d = square root of coherent energy density

δD: Energy derived from dispersion force

δP: Energy derived from polarity

δH: Energy derived from hydrogen bonding force

The wet grinding process may be characterized by chemically activating the fusion precursor obtained in plasma.

For activation, titanate-based coupling agents such as isopropyl di(dioctylphosphite) titanate, tetraoctyl bis(ditridecylphosphite)titanate, and isopropyl triisostearoyl titanate, which can disperse organic and inorganic substances on the surface, Vinyltrimethoxysilane, 3-Aminopropyltriethoxysilane, 3- Silane coupling agents such as (Trimethoxysilyl)propylsuccinic anhydride, fatty acids such as stearic acid, palmitic acid, and oleic acid, and acrylate copolymer, copolymers with pigment affinity groups, sodium alkylnaphthalenesulfonate, sodium polyacrylate , olefin-sodium maleate copolymer, carboxymethyl cellulose, alkylbenzene (naphthalene) sulfonate, fatty acid amide, polyoxyethylene alkylamine, alkylamine (acetate, fatty acid salt), alkyl secondary (tertiary) amine (amide), Amine derivatives such as alkyl imidazolines, xanthan gum, sucrose fatty acid ester, glycerin fatty acid ester, propylene glycol fatty acid ester, polyvinyl pyridolidone, polyethylene-polypropylene glycol, emulsifiers, alkyl phenols, fatty acids, higher fatty acid amines, etc. By adding a polymer-type dispersant, inorganic Si/Graphite/CNT can be activated to enable dispersion in the solvent.

The wet grinding process may be characterized by homogenizing the fusion precursor using equipment that applies shear stress and cavitation to the activated slurry.

The next step is to coat the peeled silicon-graphene-carbon nanotube composite with a binder.

Binder coating is a coating process for granulation. The binder is a resin that dissolves in a solvent and plays a binding role during coating and granulation of exfoliated particles. Thermoplastic resins, thermosetting resins, pitch and hydrocarbon resins are used. The thermoplastic binder is one of Acryl, Ethyl cellulose, Polyester, Polysulfone, Phenoxy, and Polyamide, or a mixture of at least two of them. It may be composed of, and the thermosetting binder may be one of amino, epoxy, and phenol, or a mixture of at least two or more. Pitch can be either coal-based or petroleum-based pitch. In this example, 10 wt% of coal tar pitch was added compared to the composite and mixed using a mixer.

The next step is to granulate the binder-coated, exfoliated silicon-graphene-carbon nanotube composite to produce a granulated silicon-graphene-carbon nanotube composite.

Equipment is used to obtain the desired rotational force to spheroidize the binder-coated particles, including a ball mill, attrition mill, paste mixer, and an ultra-fine grinder that can control the rotational force. Spheronization is possible by controlling the working rpm and process time, such as through mechano fusion, which can compact particles with rotational force.

Hereinafter, a negative electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described.

A negative electrode active material for a lithium secondary battery according to an embodiment of the present invention may include the silicon-graphene-carbon nanotube composite.

The anode active material made of the silicon-graphene-carbon nanotube composite, which exhibits a uniform distribution without pores and without agglomeration through dispersion, can achieve optimal charge/discharge capacity and initial efficiency of a lithium secondary battery, and can achieve cycle ( cycle) characteristics can be implemented.

Hereinafter, examples and experimental examples of the present invention will be described in detail.

<Example>

Proceed with dispersion by selecting among high shear mixer, ball mill, attrition mill, high pressure homogenizer, three roll mill, basket mill, apex mill, paste mixer, planetary mixer, spike mill, and ultrasonic. In the present invention, primary dispersion was performed by applying a Basket mill at 3000 rpm, 2 hr, and Zirconia ball 0.4 mm, and then graphite and Si were further separated by applying a 4000 Watt class ultrasonic disperser. If equipment capable of applying high shear is added later, a greater degree of peeling can be obtained.

Table 1 shows the process conditions of existing comparative examples and manufacturing examples according to the manufacturing process. A pigment-friendly copolymer dispersant was applied for plasma treatment and activation, and coin half cells were manufactured by varying the boiling point between 60 and 160°C and the Hansen solubility parameter.

<Experimental Example 1> Cross section of silicon-graphene-carbon nanotube composite according to dispersion

Figure 4 is an FE-SEM image of a cross section of a silicon-graphene-carbon nanotube composite. Referring to Figure 4, it can be seen that a layer of silicon particles uniformly dispersed and distributed on the graphene layer and a layer of carbon nanotubes wrapping the silicon in various directions were observed.

<Experimental Example 2> Electrochemical evaluation

Figure 5 is a graph of electrochemical evaluation of (a) Comparative Example and (b) Example. Figure 6 is a cycle retention graph of comparative examples and examples. Table 2 shows these data.

Through this, it can be confirmed that in the case of a mixed electrode manufactured using a silicon-graphene-carbon nanotube composite, the initial discharge capacity, initial efficiency, cycle capacity change, and capacity maintenance rate are improved when applied as a negative electrode active material.

The description of the present invention described above is for illustrative purposes, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential features of the present invention. will be. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. For example, each component described as single may be implemented in a distributed manner, and similarly, components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the patent claims described below, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention.

Claims (10)

Includes an external pitch coating layer,
The cross section containing the center is
Graphene layer;
A carbon nanotube layer located on the graphene layer and including a plurality of carbon nanotubes; and
A silicon-graphene-carbon nanotube composite comprising a nano-silicon particle layer located on the graphene layer and including a plurality of nano-silicon particles bonded to the carbon nanotubes.
According to paragraph 1,
A silicon-graphene-carbon nanotube composite, characterized in that the thickness of the graphene layer is 1 nm to 300 nm.
According to paragraph 1,
The carbon nanotubes have a length of 0.1 to 30 um, a specific surface area of 100 to 500 m ² /g, a bulk density of 0.05 to 0.2 g/cm ³ , a purity of 95% or more, and a single wall or multi-layer wall. A silicon-graphene-carbon nanotube composite, characterized in that it is (multi wall).
According to paragraph 1,
A silicon-graphene-carbon nanotube composite, characterized in that the thickness of the pitch coating layer is 0.05 to 1 μm.
According to paragraph 1,
A silicon-graphene-carbon nanotube composite, characterized in that the silicon content is more than 0 and less than 85 wt%.
Preparing a silicon-graphite-carbon nanotube fusion precursor;
Plasma processing the silicon-graphite-carbon nanotube fusion precursor;
forming an exfoliated silicon-graphene-carbon nanotube composite by dispersing the plasma-treated silicon-graphite-carbon nanotube fusion precursor through a wet grinding process;
Coating the peeled silicon-graphene-carbon nanotube composite with a binder; and
Granulating the binder-coated exfoliated silicon-graphene-carbon nanotube composite to produce a granulated silicon-graphene-carbon nanotube composite; including, silicon-graphene- Carbon nanotube composite manufacturing method.
According to clause 6,
The binder coating is a silicon-graphene-carbon nanotube composite manufacturing method, characterized in that the pitch liquid (pitch) is coated.
According to clause 6,
A method for producing a silicon-graphene-carbon nanotube composite, characterized in that the solvent used in the wet grinding process has a Hansen Solubility Parameter of 17 to 23 MPa ½ or 45 to 50 MPa ½.
According to clause 6,
A method for producing a silicon-graphene-carbon nanotube composite, characterized in that the solvent used in the wet grinding process has a boiling point of 60 to 160 ° C.
A negative electrode active material for a lithium secondary battery comprising the silicon-graphene-carbon nanotube composite of claim 1.