KR20220133692A - Method of manufacturing composite for anode material prepared carbon nanotube, composite for anode material prepared therefrom, and secondary battery comprising same - Google Patents

Abstract

The present invention relates to a method for preparing a composite for a negative electrode material including a pre-treated carbon nanotube, a composite for a negative electrode material prepared thereby, and a secondary battery including the same. The method of the present invention comprises the steps of: preparing a mixed solution including graphene oxide, a silicon-based particle, a carbon nanotube, and a solvent; spraying and drying the mixed solution to coat the graphene oxide on the silicon-based particle while the solvent evaporates, and preparing a composite particle where a carbon nanotube is bound to the graphene oxide; and thermally treating the composite particle to perform the reduction of the graphene oxide and the carbon nanotube.

Description

A method for manufacturing a composite for an anode material comprising a pretreated carbon nanotube, a composite for an anode material prepared therefrom, and a secondary battery comprising the same SECONDARY BATTERY COMPRISING SAME}

The present invention relates to a method for manufacturing a composite for an anode material including a pretreated carbon nanotube, a composite for an anode material prepared therefrom, and a secondary battery including the same.

Recently, as the demand for ultra-large power storage systems along with miniaturized and light-weighted various electronic devices has rapidly increased, global interest in new energy sources is increasing. Among them, R&D is focused on the secondary battery field, which is environmentally friendly, has high energy density, and can be charged and discharged rapidly.

For example, lithium secondary batteries are gaining importance not only as power sources for portable electronic devices, but also as non-IT power sources such as hybrid vehicles, plug-in hybrid vehicles and electric vehicles, and industrial tools and robots. In addition, it is expected that its use will be expanded as a large-capacity energy storage device in order to improve the power quality caused by the intermittent power generation for the wide distribution of new and renewable energy such as solar and wind power generation.

The performance of a lithium secondary battery is very important to the application of a lithium secondary battery, and compared to the performance of the existing lithium secondary battery, the storage capacity (active material unit weight or charging capacity per unit volume), output (active material unit weight or discharging rate per unit volume), stability and The demand for the development of lithium secondary batteries with improved lifespan (the number of repeatable charge/discharge while maintaining storage capacity) characteristics is continuously increasing. These characteristics are primarily determined by the characteristics of the negative active material used as the negative electrode material.

Graphite is used as an anode material for existing lithium secondary batteries, but the maximum theoretical capacity that can be stored is about 372 mAh/g. In order to increase the capacity, it is necessary to develop an anode material with a storage capacity higher than that of graphite.

Among the anode material candidates for lithium secondary batteries that can replace graphite, metal groups (Si, Sn, As, Ge, Bi, Al, In, Pb, and Ga) that electrochemically react with lithium to form an alloy are of interest as high-capacity materials. is dragging

Among them, silicon has a high theoretical capacity (~4,200mAh/g) and a low charge potential (~0.2V vs Li/Li ⁺ ) and is a rich resource. have.

However, due to the large volume change (>300%) that occurs when lithium ions are charged and discharged, polarization and cracking of the anode occur. ) is continuously generated to increase internal resistance, resulting in low efficiency and reduced capacity during cycle repetition, resulting in shortened lifespan. In addition, since silicon has very low electrical conductivity, a method of manufacturing it in the form of a composite with a conductive material is required.

To this end, in 'a method for manufacturing a crumpled-shaped silicon-carbon nanotube-graphene composite, and a secondary battery (registration number: 10-1813893) including the composite and composite prepared accordingly', silicon, carbon nanotubes, graphene oxide and A method for preparing a silicon-carbon nanotube-graphene composite having a crumpled shape by preparing a mixture containing a solvent, spray-drying it, and then heat-treating it has been proposed.

However, since reduction of carbon nanotubes and graphene oxide is achieved only by heat treatment at a temperature of 500 to 1,000 ° C in at least one gas atmosphere selected from the group consisting of argon, helium and nitrogen, a high temperature of at least 500 ° C is required, There is a problem in that a separate inert gas atmosphere must be provided.

Therefore, technology development research on silicon-based anode materials for secondary batteries using graphene oxide that can be reduced without heat treatment in a high-temperature inert gas atmosphere and carbon nanotubes with excellent electrical conductivity is urgently required.

Registered in Korea Patent Publication No. 10-1420049, 2014.07.09.

The present invention was invented to solve the above problems, and includes a silicon-based pretreated carbon nanotube using graphene oxide, which can be reduced without heat treatment under a high-temperature inert gas atmosphere, and carbon nanotubes with excellent electrical conductivity. It is a technical solution to provide a method for manufacturing a composite for an anode material, a composite for an anode material prepared therefrom, and a secondary battery including the same.

In order to solve the above technical problem, the present invention comprises the steps of: preparing a mixed solution containing graphene oxide, silicon-based particles, carbon nanotubes, and a solvent; preparing composite particles in which the graphene oxide is coated to surround the silicon-based particles as the solvent evaporates by spray-drying the mixed solution, and the carbon nanotubes are bonded to the graphene oxide; and reducing the graphene oxide and the carbon nanotube by heat-treating the composite particle, wherein the carbon nanotube is a composite powder in which the carbon nanotube and the metal salt compound are mixed, and a shear stress in an acid solution. preparing a carbon nanotube liquid crystal phase in which the metal salt compound is co-intercalated between adjacent layers of the carbon nanotube by adding and mixing; heating the carbon nanotube liquid crystal phase to prepare a carbon nanotube into which an oxygen-containing functional group is introduced by the metal salt compound and an acid solution; and washing and filtering the carbon nanotube into which the oxygen-containing functional group is introduced; .

In the present invention, the graphene oxide includes an oxygen-containing functional group that is an epoxy group or a hydroxyl group on the surface, but an oxygen-containing functional group that is a lactol group or a carboxyl group does not exist on the surface, so it is high heat-resistant graphene oxide showing thermal stability, The heat treatment is characterized in that it is made in a temperature range showing the thermal stability of the high heat-resistant graphene oxide.

In the present invention, the graphene oxide is high heat-resistant graphene oxide exhibiting thermal stability at 170 to 450° C., and the heat treatment of the composite particles includes heat-treating the high heat-resistant graphene oxide at 170 to 450° C. It is characterized by reduction.

In the present invention, the graphene oxide is prepared by mixing graphite and a chlorate-based oxidizing agent in a powder state, adding concentrated nitric acid to oxidize the graphite oxide, and using a basic solution that does not contain metal ions under alkaline conditions of pH 10 or higher It is characterized in that it is a high heat-resistant graphene oxide dispersion solution prepared by exfoliating the graphite oxide.

In the present invention, the silicon-based particles, but any one or more of silicon, a silicon alloy and silicon oxide, the metal element contained in the silicon alloy is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, It is characterized in that at least one selected from the group consisting of Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, and Po.

In the present invention, the carbon nanotube is prepared by further comprising; dispersing the pretreated carbon nanotube in a solvent to prepare a carbon nanotube dispersion, and the pretreated carbon nanotube dispersion is in a liquid crystal form It is characterized in that self-assembly is possible.

In the present invention, the carbon nanotube, single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (double-walled carbon nanotube, DWCNT) and multi-walled carbon nanotube (multi-walled carbon) nanotube, MWCNT), characterized in that at least one of them.

In the present invention, the metal salt compound is any one or more of nitrate, sulfate and phosphate, wherein the nitrate is sodium nitrate (NaNO ₃ ), potassium nitrate (KNO ₃ ) and calcium nitrate (Ca(NO ₃ ) ₂ ). at least one selected from the group, wherein the sulfate is sodium sulfate (Na ₂ SO ₄ ), potassium sulfate (K ₂ SO ₄ ), sodium hydrogen sulfate (NaHSO ₄ ) and potassium hydrogen sulfate (KHSO ₄ ) Selected from the group consisting of It is at least one, and the phosphate salt is characterized in that at least one selected from the group consisting of dipotassium phosphate (K ₂ HPO ₄ ) and potassium phosphate (KH ₂ PO ₄ ).

In the present invention, the step of preparing the liquid crystal phase is characterized in that the shear stress is applied by stirring for 30 minutes to 3 hours at a rotation speed of 100 to 2,000 rpm.

In the present invention, the step of preparing the liquid crystal phase is characterized in that the shear stress is applied using any one or more of an impeller, a paste mixer, and a Kuett-Taylor reactor.

In the present invention, the step of preparing the liquid crystal phase is characterized in that the shear stress is applied using any one or more of an impeller, a paste mixer, and a Kuett-Taylor reactor.

In the present invention, in the step of preparing the liquid crystal phase, the carbon nanotubes and the metal salt compound are mixed in a weight ratio of 1:0.1 to 10 to form a composite powder.

In the present invention, the step of preparing the carbon nanotube into which the oxygen-containing functional group is introduced is characterized in that the liquid crystal phase is heated at 25 to 150°C.

In the present invention, in the step of preparing the carbon nanotube into which the oxygen-containing functional group is introduced, an oxidizing agent is further added to the liquid crystal phase and stirred, and then the liquid crystal phase is heated to introduce the oxygen-containing functional group. characterized in that it is manufactured.

In order to solve the above other technical problems, the present invention provides a composite prepared by the above method.

In order to solve the another technical problem, the present invention, a positive electrode; a negative electrode including the composite; a separator provided between the anode and the cathode; and an electrolyte; provides a secondary battery comprising.

According to the method for producing a composite for an anode material comprising a pretreated carbon nanotube of the present invention by means of solving the above problems, an oxygen-containing functional group that is an epoxy group or a hydroxy group is included on the surface, and an oxygen-containing functional group that is a lactol group or a carboxyl group There is an effect that can be reduced through heat treatment in an air atmosphere in a temperature range showing the thermal stability of high heat-resistant graphene oxide by using high-heat-resistant graphene oxide that does not exist on the surface and shows thermal stability.

In addition, since a large number of sp ² bonds exist on the surface of graphene oxide, and hydroxyl and epoxy groups having a relatively lower oxidation degree than carboxyl and lactol groups exist on the surface, most of the hydroxyl and epoxy groups are removed at 170 to 250 ° C. After heat treatment, deterioration proceeds very slowly, and as it has thermal stability to minimize deterioration, heat treatment, which was conventionally performed at a high temperature of 500 to 1,000 ° C under an inert gas atmosphere, can be performed at a low temperature and in air, resulting in a process unit cost It has the effect of lowering the cost and significantly improving the convenience and efficiency of the process.

In addition, since the metal salt compound can be co-intercalated between adjacent interlayers of the carbon nanotubes to form a self-assembled structure of the carbon nanotubes, the dispersibility of the carbon nanotubes is improved and eventually the aggregation of the carbon nanotubes is reduced. It has a resolving effect.

In addition, since the use of graphene oxide and carbon nanotubes, which can be reduced without heat treatment under a high temperature inert gas atmosphere due to minimized defects, is used, there is an effect of improving the electrical conductivity of a silicon-based anode material for a secondary battery.

1 is a flowchart showing a method of manufacturing a composite for an anode material including a carbon nanotube pretreated according to the present invention.
2 is a chemical structure showing a conventional graphene oxide in which a lactol group or a carboxyl group is present on the surface.
3 is a chemical structure showing high heat resistance graphene oxide having an epoxy group or a hydroxyl group on the surface according to the present invention.
Figure 4 (a) is a graph showing the ¹³ C solid-state NMR analysis result of high heat-resistant graphene oxide according to the present invention, Figure 4 (b) is a graph showing the ¹³ C solid-state NMR analysis result of the conventional graphene oxide.
5 is a graph showing the analysis of ¹³ C solid-state NMR calculated as the area ratio (area%) of FIG. 4(a).
6 is a graph showing thermogravimetric analysis (TGA) results of high heat-resistant graphene oxide according to the present invention and conventional graphene oxide.
7 is a graph showing the results of ultraviolet-visible light spectroscopy of high heat-resistant graphene oxide according to the present invention and conventional graphene oxide.
8 is a flowchart showing a method for preparing a carbon nanotube dispersion using the pretreated carbon nanotubes according to the present invention.
9 is a schematic diagram showing the rotation and revolution according to the present invention.
10 is a SEM photograph showing a carbon nanotube dispersion pretreated according to the present invention.
11 is a SEM photograph showing a carbon nanotube dispersion that has not been pretreated.
12 is a schematic view showing a composite for an anode material according to the present invention.
13 is a graph showing the thermal behavior of the carbon oxide nanotube according to Example 2.
14 is an SEM photograph showing Example 3.
15 is a graph showing the thermogravimetric analysis (TGA) results of Example 3.
16 is a graph showing the results of Raman spectroscopy of Example 3.
17 is a graph showing a capacity retention rate according to a charge/discharge cycle of an electrode.
18 is a graph showing the coulombic efficiency according to the charge/discharge cycle of the electrode.
19 is a graph showing the rate characteristics according to the charge/discharge cycle of the electrode.

Hereinafter, the present invention will be described in detail.

1 is a flowchart showing a method of manufacturing a composite for an anode material including a carbon nanotube pretreated according to the present invention. Referring to FIG. 1 , the composite for anode material including carbon nanotubes pretreated according to the present invention is prepared by preparing a mixed solution including graphene oxide, silicon-based particles, carbon nanotubes and a solvent (S10) and mixing; A step (S20) of preparing composite particles in which graphene oxide is coated to surround silicon-based particles, and carbon nanotubes are bonded to graphene oxide as the solvent is evaporated by spray-drying the solution, and graphene oxide by heat-treating the composite particles Through the step of reducing the and carbon nanotubes (S30), it can be prepared into a high heat-resistance graphene-silicon-carbon nanotube composite.

According to the above-described manufacturing method, first, a mixed solution containing graphene oxide, silicon-based particles, carbon nanotubes, and a solvent is prepared (S10).

Graphene oxide contains an oxygen-containing functional group that is an epoxy group or a hydroxyl group on the surface, but an oxygen-containing functional group with a high degree of oxidation such as a lactol group or a carboxyl group does not exist on the surface. The heat treatment is performed in air in a temperature range showing the thermal stability of graphene oxide. Accordingly, heat treatment, which was conventionally performed at a high temperature of 500 to 1,000° C. under an inert gas atmosphere, can be performed at a low temperature and in air, thereby remarkably improving the process.

In relation to this, FIG. 2 shows a chemical structure of graphene oxide having a conventional lactol group or a carboxyl group on the surface, and FIG. 3 is a chemical structure of graphene oxide having high heat resistance having an epoxy group or a hydroxyl group on the surface according to the present invention. will be.

As shown in FIG. 2, conventional graphene oxide oxidizes graphite using a strong acid and an oxidizing agent to produce graphite oxide, and then peels off the surface and edges to have good chemical reactivity, such as epoxy groups, carbonyl groups, carboxyl groups, hydroxyl groups, and lactol groups. It has a structure in which all oxygen-containing functional groups are introduced. In other words, as oxygen-containing functional groups are introduced through oxidation of graphite, carboxyl groups and lactol groups, which have a relatively higher oxidation degree than epoxy groups and hydroxyl groups, exist on the surface of graphene oxide, so they are easily deteriorated at high temperatures such as 400° C. or higher, resulting in thermal stability. It can be seen that this is lacking.

On the other hand, the high heat-resistant graphene oxide according to the present invention as shown in FIG. 3 has an epoxy group and a hydroxyl group on the surface, and the carboxyl group and lactol group having a relatively high degree of oxidation do not exist on the surface, so heat resistance that is not easily deteriorated at high temperature shows stability.

4 is a graph showing the ¹³ C solid-state NMR analysis results of high heat-resistant graphene oxide according to the present invention and conventional graphene oxide, FIG. 4 (a) is a ¹³ C solid-state NMR of high heat-resistant graphene oxide used in the present invention The analysis result, Figure 4 (b) is a graph showing the ¹³ C solid-state NMR analysis result of the conventional graphene oxide.

Referring to this, it can be confirmed that the high heat-resistant graphene oxide shown in FIG. 4(a) has a carbon-carbon double bond, a hydroxyl group, and an epoxy group emerging from the graphite structure, and a carboxyl group and a lactol group do not exist on the surface, and FIG. It is confirmed that the conventional graphene oxide shown in 4(b) has a hydroxyl group and a carbonyl group, a carboxyl group, and a lactol group, which have a relatively higher oxidation degree than that of epoxy.

Figure 5 shows a graph analyzing ¹³ C solid NMR calculated as the area ratio (area%) of Figure 4(a). Referring to this, the hydroxyl group is 47.3%, the epoxy group is 32.6%, and the oxidation degree is 79.9% in total. is confirmed to be high, and the ratio of carbon-carbon double bonds is 20.1%.

6 is a graph showing thermogravimetric analysis (TGA) results of high heat-resistant graphene oxide according to the present invention and conventional graphene oxide, line 1 of FIG. 6 is conventional graphene oxide, and line 2 is oxidation of the present invention graphene is shown. However, the measurement of the solid content of graphene oxide as in FIG. 6 may be performed at 0.5 to 5° C./min in air by thermogravimetric analysis.

This indicates how much solid content is left by burning graphene oxide in air while the temperature is raised from 100°C to 450°C starting at room temperature. It was found that the solid content was maintained at 95% by weight or more at 200°C, and the solid content remained in an amount of 65 to 80% by weight or less at 400°C. On the other hand, it is confirmed that the conventional graphene oxide (line 1) has a solid content of 80% by weight or less at 200°C, and a lot of oxidation occurs in air at 400°C, and the solid content drops rapidly to 60% by weight or less.

That is, conventional graphene oxide having an oxygen-containing functional group is easily deteriorated in air and burns due to its characteristics, and the high heat-resistant graphene oxide used in the present invention has thermal stability to withstand such heat up to about 450°C. Specifically, high heat-resistant graphene oxide (line 2) is maintained in a state close to 100% by weight because the solid content does not decrease at a relatively low temperature range of 100 to 170°C, and at 170 to 250°C, the oxygen-containing functional group is removed and the weight is It can be seen that the pattern is rapidly decreased, and the solid content is maintained in an amount of 65 to 80% by weight or less at 250 to 450° C. and stabilized again.

The reason for showing a high solid content of 95% by weight or more even at 200°C in the present invention as shown in FIG. 6 is that the carboxyl group and lactol group, which have a relatively high degree of oxidation than the epoxy group and the hydroxyl group, do not exist on the surface, resulting in a relative temperature of 170 to 250°C. At a low temperature, only the epoxy group and the hydroxyl with a low oxidation degree are removed and reduced to graphene having a hexagonal structure having an sp ² bond structure. % or more will be maintained.

In addition, Figure 7 shows the ultraviolet-visible spectroscopic analysis graph of the high heat-resistant graphene oxide according to the present invention and the conventional graphene oxide, where peak 1 is high heat-resistant graphene oxide used in the present invention, and peak 2 is conventional oxidation represents graphene. Referring to this, in peak 1, unlike peak 2, polycyclic aromatic hydrocarbons (PAHs) that form sp ² bonds between carbon atoms appear. After the hydroxyl group is removed at 200 to 250 ℃, it is formed by reduction with a polycyclic aromatic hydrocarbon.

From the results of FIGS. 2 to 7 as described above, the high heat-resistant graphene oxide used in the present invention does not have a lactol group and a carboxyl group with a high degree of oxidation on the surface, so it has a lot of the original graphene structure after heat treatment, Since there is no inducing structure, it can be confirmed that the thermal stability is not easily deteriorated in the temperature range of 250 to 450 °C.

Preferably, in the present invention, the high heat-resistant graphene oxide has a structure in which an oxygen-containing functional group that is an epoxy group or a hydroxyl group is included on the surface, and an oxygen-containing functional group that is a lactol group or a carboxyl group does not exist on the surface, so that graphite and chlorate (chlorate, ClO ₃ ^- )-based oxidizing agent is mixed in a powder state, and graphite oxide is prepared by oxidizing by adding concentrated nitric acid, and in alkaline conditions of pH 10 or higher with a basic solution that does not contain metal ions, By peeling the prepared graphite oxide, a high heat-resistant graphene oxide dispersion solution can be prepared.

More specifically, graphite and a chlorate-based oxidizing agent are mixed in a powder state, and then a small amount of a strong acid such as concentrated nitric acid is added to oxidize at room temperature, and then the graphite oxide is substituted with an oxygen-containing functional group on the surface or edge to form graphite oxide. Thereafter, by controlling the pH to 10 or more with a basic solution that does not contain metal ions in graphite oxide and applying temperature to peel it, lactol groups and carboxyl groups, which have a relatively higher degree of oxidation than epoxy groups and hydroxyl groups, are removed from the surface. can be excluded. Through this, the lactol group and the carboxyl group are not removed through a separate treatment process from graphene oxide in which an epoxy group, a hydroxyl group, a lactol group, and a carboxyl group are bonded to the surface and edges. This results in the formation of graphene oxide that does not exist.

That is, the conventional graphene oxide contains a large number of oxygen-containing functional groups with a high oxidation degree as the graphite is oxidized using a strong oxidizing agent such as sulfuric acid and potassium permanganate, whereas the graphene oxide with high heat resistance of the present invention is used when the graphite is oxidized. The chlorate-based oxidizing agent used is to give a property that prevents the formation of a lactol group and a carboxyl group. Here, when the graphite oxide is separated or peeled off, it is made under alkaline conditions using a basic solution that does not contain metal ions, so that lactol and carboxyl groups are not formed and metal ions are not contained so that oxidation of the metal does not occur, resulting in heat resistance stability will have

When graphite oxide is peeled off, if it is made under alkaline conditions using a basic solution containing metal ions such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), it oxidizes itself due to the metal, and metals such as sodium ions or potassium ions Since the ions are attached to the surface of the graphene oxide, the metal ions in the graphene oxide are easily deteriorated and thus thermal stability cannot be exhibited. Furthermore, in the process of synthesizing graphene oxide using graphite in the conventional graphene oxide, an oxygen-containing functional group is introduced into graphene as graphite is oxidized. An empty space is created. At this time, the oxygen-containing functional group is easily introduced into the empty space, and it starts to burn from here and rapidly deteriorates at a high temperature such as 400° C. or higher, so that high heat resistance cannot be stably achieved.

On the other hand, as described above, graphene oxide with high heat resistance used in the present invention is oxidized by a chlorate-based oxidizing agent to prepare graphite oxide in which lactol groups and carboxyl groups are not formed, and a basic solution containing no metal ions is used. By exfoliating the graphite oxide to form graphene oxide, the original graphene structure in which the carbon-carbon double bond forms an sp ² hybrid orbital can be generated without forming empty spaces.

However, the graphene oxide of the present invention includes an oxygen-containing functional group that is an epoxy group or a hydroxyl group on the surface, but a high-heat-resistant graphene oxide exhibiting thermal stability because an oxygen-containing functional group with a high degree of oxidation such as a lactol group or a carboxyl group does not exist on the surface In addition to fins, commercially available graphene oxide is also applicable.

The silicon-based particle is a silicon-based metal particle, and may be variously applied as long as it is a nano- or micro-sized silicon-based metal particle. That is, silicon-based particles of any one or more of silicon, silicon alloy, and silicon oxide may be used. Metal elements included in the silicon alloy are Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, and may be at least one selected from the group consisting of Po.

Carbon nanotubes may be formed by preparing a carbon nanotube that has been pretreated to increase dispersibility of the carbon nanotubes without using a dispersant, and using this to prepare a carbon nanotube dispersion.

In relation to this, FIG. 8 is a flowchart showing a method for preparing a carbon nanotube dispersion using the pretreated carbon nanotube according to the present invention, and the pretreated carbon nanotube of the present invention is prepared, and the carbon nanotube is used A method of preparing a dispersion is a composite powder in which carbon nanotubes and a metal salt compound are mixed in a solid state, and an acid solution is mixed while applying a shear stress, and the metal salt compound is co-intercalated between adjacent layers of carbon nanotubes. Co-intercalation) preparing a carbon nanotube liquid crystal phase (S1) and heating the carbon nanotube liquid crystal phase to prepare a carbon nanotube into which an oxygen-containing functional group that is a carboxyl group or a hydroxyl group is introduced by a metal salt compound and an acid solution (S2), washing and filtering the carbon nanotube into which the oxygen-containing functional group is introduced, to prepare a pretreated carbon nanotube (S3), and dispersing the pretreated carbon nanotube in a solvent to the carbon nanotube and preparing a dispersion (S4).

However, the pretreatment described in the present invention is a process in which the metal salt compound is co-intercalated between adjacent interlayers of the carbon nanotubes through shear stress, and oxygen-containing functional groups are introduced into the carbon nanotubes through heat treatment. .

In order to pre-treat the carbon nanotubes, first, the carbon nanotubes and the metal salt compound are mixed in a solid state to form a composite powder, and the composite powder and acid solution thus formed are mixed while applying a shear stress, so that the metal salt compound is the carbon nanotube. A carbon nanotube liquid crystal phase co-intercalated between adjacent layers is prepared (S1).

Prior to the description, carbon nanotubes are single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (DWCNT), and multi-walled carbon nanotube (MWCNT). ), any one or more of them may be used.

Among them, single-walled carbon nanotubes have a diameter of only 1 nm, so they do not exist alone, and exhibit characteristics of agglomeration due to van der Waals attraction. Due to these characteristics, single-walled carbon nanotubes originally have a bundle structure, but in the past, many techniques have been made in the direction of dismantling the bundle structure of single-walled carbon nanotubes. In other words, when the bundle of single-walled carbon nanotubes grows, dispersion is not good, so in terms of the dispersion concept, the bundle is made smaller to improve dispersibility and to minimize the bundle size to maximize electrical conductivity. Also, in the prior art, there was only a method of using a super acid to make a single-walled carbon nanotube into a liquid crystal phase, so it was difficult to treat the super acid in the air, so it had to be treated in a glove box.

In the case of multi-walled carbon nanotubes, aggregation occurs due to their large diameter, but rather shows similar characteristics to the entanglement of polymer chains. and some having a large diameter have properties similar to those of multi-walled carbon nanotubes.

Although carbon nanotubes with these characteristics are in the spotlight as a conductive material due to their unique electrical, thermal, and physicochemical properties, it is difficult to secure dispersion stability due to aggregation such as bundling or entanglement. In particular, since the aggregation of carbon nanotubes is difficult to physically treat, it has been difficult to prepare a carbon nanotube dispersion.

Therefore, in order to prevent the carbon nanotubes from being aggregated or precipitated in the solvent and to disperse them in a stable state, a method for pre-treating the carbon nanotubes is required. In this step, the carbon nanotubes are mixed with a metal salt compound in a solid state. A composite powder is prepared, and then the composite powder and the acid solution are mixed while applying a shear stress to prepare a carbon nanotube liquid crystal phase.

The metal salt compound used for preparing the liquid crystal phase may be any one or more of nitrate, sulfate, and phosphate. The nitrate may be at least one selected from the group consisting of sodium nitrate (NaNO ₃ ), potassium nitrate (KNO ₃ ), and calcium nitrate (Ca(NO ₃ ) ₂ ), and the sulfate is sodium sulfate (Na ₂ SO ₄ ), sulfuric acid At least one may be selected from the group consisting of potassium (K ₂ SO ₄ ), sodium hydrogen sulfate (NaHSO ₄ ) and potassium hydrogen sulfate (KHSO ₄ ), and the phosphate is dipotassium phosphate (K ₂ HPO ₄ ) and potassium phosphate. (KH ₂ PO ₄ ) At least one selected from the group consisting of may be used through mixing. The acid solution may be at least one selected from the group consisting of sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), hydrogen peroxide (H ₂ O ₂ ), and hydrochloric acid (HCl). However, the metal salt compound and the acid solution are not limited to the above types, and various materials can be used as long as they can be included in the metal salt compound and the acid solution.

The reason that the carbon nanotubes and the metal salt compound are first mixed in a powder state using a mixer or the like before adding the acid solution that functions as a solvent and an oxidizer is that the metal salt compound can easily penetrate between adjacent layers of the carbon nanotubes. This is to increase functionalization efficiency by creating a co-intercalation structure.

At this time, it is preferable to form a liquid crystal phase by minimizing the amount of the metal salt compound in the composite powder. Usually, the metal salt compound is added in excess of about 10 times the amount of carbon nanotubes, and since shear stress is used in this step, it is sufficient that the metal salt compound is mixed in a ratio of 0.1 to 10 weight ratio to 1 weight ratio of carbon nanotubes.

If the metal salt compound is less than 0.1 weight ratio, it is difficult to functionalize the inside, the surface and the terminal of the carbon nanotube with an oxygen-containing functional group such as a carboxyl group or a hydroxyl group. As a result, the oxygen-containing functional groups introduced into the carbon nanotubes are reduced, and eventually, the carbon nanotubes cannot be self-assembled in the carbon nanotube dispersion and are inevitably dispersed in a disorderly direction. In order to form a self-assembly of the carbon nanotubes by introducing an oxygen-containing functional group to the carbon nanotubes by applying a shear stress, it is preferable that the metal salt compound be at least 0.1 weight ratio relative to 1 weight ratio of the carbon nanotubes. On the other hand, if the metal salt compound exceeds 10 weight ratio with respect to 1 weight ratio of carbon nanotubes, it is impossible to minimize the metal ions in the carbon nanotube dispersion.

On the other hand, the carbon nanotube liquid crystal phase forms a structure in which the metal salt compound is co-intercalated between adjacent interlayers of the carbon nanotubes through shear stress. That is, when a shear stress is applied to the composite powder and the acid solution, the metal salt compound is co-intercalated between adjacent layers in the carbon nanotube, and the metal salt compound is solvated by the acid solution between adjacent layers of the carbon nanotube. can be placed between them. The carbon nanotube liquid crystal phase co-intercalated so that the metal salt compound is positioned between the layers of the carbon nanotube can be self-assembled in the form of a liquid crystal phase when it is later formed into a carbon nanotube dispersion.

The shear stress is applied according to the rpm control, which is the stirring speed, and it is preferable to apply the shear stress while stirring at a rotation speed of 100 to 2,000 rpm. If the rotational speed is less than 100 rpm, it is insufficient to create a co-intercalation structure in which a metal salt compound is disposed between adjacent interlayers of the carbon nanotubes. It is difficult to sufficiently make an oxygen-containing functional group such as a hydroxyl group. If it is rotated at a speed exceeding 2,000 rpm, it is undesirable because the carbon nanotube may be re-aggregated by causing a shape deformation of the carbon nanotube.

In addition, the shear stress is preferably applied within the range of 30 minutes to 3 hours. If a shear stress is applied for less than 30 minutes, the time for the metal salt compound to be located between the layers of carbon nanotubes in the liquid crystal phase is insufficient, and the metal salt compound not located between the layers of the carbon nanotubes remains disorderly in the liquid crystal phase. Therefore, it is not efficient to prepare a carbon nanotube dispersion. When the shear stress is applied for more than 3 hours, it is inefficient in terms of the process because it does not exhibit a better intercalation action compared to the case where it is carried out for a time less than that.

As a method of applying the shear stress, any one or more of an impeller, a Couette-Taylor reactor, and a paste mixer capable of rotation and revolution can be used. The stronger the shear stress, the shorter the time to form the liquid crystal phase be able to do

For example, stirring can be performed by double rotation of rotation and revolution using a paste mixer, which can be seen through FIG. 9 schematically showing rotation and revolution according to the present invention. Referring to FIG. 9 , after injecting a composite powder and an acid solution in which carbon nanotubes and a metal salt compound are mixed in a powder state into at least one container 100 , the container is tilted at a preset angle with respect to the rotation axis R1 . At the same time as it rotates around the orbital axis (R2), centrifugal force and shear stress are generated, and a carbon nanotube liquid crystal phase forming a structure in which the metal salt compound is intercalated between adjacent interlayers of the carbon nanotube will be formed. can

That is, the revolution of the plurality of containers 100 radially connected to the orbital axis R2 about the orbital axis R2, which can be the central rotational axis, and the rotation by the rotational axis R1 of the center of each container 100 are simultaneously performed By proceeding, the stirring force is improved, so that a carbon nanotube liquid crystal phase having a co-intercalation structure can be prepared between the adjacent interlayers of the carbon nanotube with the metal salt compound.

The rotation speed by the rotation axis (R1) of the container 100 and the rotation speed by the rotation axis (R2), which is the central rotation axis, may be in a ratio of 0.1 to 10: 1. If the rotational speed is less than 0.1, the rotational speed is too slow compared to the orbital speed, so that the centrifugal force and shear stress enough to form a cointercalation structure on the liquid crystal are not generated, so that the carbon nanotube dispersion does not have a self-assembled structure. When the rotation speed exceeds the ratio of 10, the rotation speed is too fast than the revolving speed, so that the metal salt compound cannot be stably positioned between the carbon nanotube layers, which is also not suitable for forming a co-intercalation structure in the liquid crystal phase.

The rotation axis (R1) may be rotated in the same direction as the orbital axis (R2) based on the rotational motion of the orbital axis (R2), but in order to form a cointercalation structure in the liquid crystal phase, the rotation axis (R1) and the orbital axis (R2) ) can be rotated in opposite directions. When the rotation shaft (R1) and the orbital shaft (R2) are rotated in opposite directions to each other, the rotational shaft (R1) and the orbital shaft (R2) are rotated at the same speed to split the power.

If the carbon nanotube liquid crystal phase is not formed first by applying a shear stress, and the composite powder in which the carbon nanotubes and the metal salt compound are mixed, and the acid solution are directly heated, the metal salt compound is converted into carbon in the carbon nanotube dispersion. Since the nanotubes can be transformed into oxygen-containing functional groups without being positioned between adjacent interlayers of the nanotubes, a composite powder in which the carbon nanotubes and the metal salt compound are mixed in a solid state before heating the carbon nanotube liquid crystal phase, and an acid It can be said that it is an important process to first apply a shear stress to the solution to form a liquid crystal phase.

Then, the carbon nanotube liquid crystal phase is heated to prepare a carbon nanotube into which an oxygen-containing functional group, which is a carboxyl group or a hydroxyl group, is introduced by a metal salt compound and an acid solution (S2).

Prior to this, stirring may be performed by further adding an oxidizing agent to the liquid crystal phase, and if the oxidizing agent can be added before heat treatment through heating, it may be carried out. That is, an oxidizing agent (eg, sulfuric acid, nitric acid, etc.) can be added to the liquid crystal phase, which means that when oxidation by the metal salt compound used in the process of forming the carbon nanotube liquid crystal phase is insufficient, an oxidizing agent can be further added.

When heat treatment is performed after oxidation treatment using an additional oxidizing agent, the metal salt compound positioned in a solvated state by an acid solution between the adjacent interlayers of the carbon nanotube, and the inside, surface, or surface of the carbon nanotube by the acid solution An oxygen-containing functional group such as a carboxyl group and a hydroxyl group may be introduced at the terminal.

The heat treatment may be carried out at 150° C. or less, preferably in the range of 25 to 150° C. In addition, the heat treatment is preferably performed for 30 minutes to 24 hours, most preferably 1 hour to 10 hours.

When the carbon nanotube liquid crystal phase is heated at less than 25° C. or less than 30 minutes, a lot of time is consumed until oxygen-containing functional groups are formed in the carbon nanotubes, and when the carbon nanotube liquid crystal phase exceeds 150° C. or exceeds 24 hours, the carbon nanotube liquid crystal In the case of heating the phase, it does not take much time for the oxygen-containing functional group to be sufficiently introduced into the carbon nanotubes, so the process time can be reduced, but rather, the defect structure is excessively formed in the carbon nanotubes, which reduces the electrical conductivity. This is undesirable because it may cause a phenomenon.

Then, the carbon nanotube into which the oxygen-containing functional group is introduced is washed and filtered to prepare a pretreated carbon nanotube (S3).

That is, neutralization and washing are performed to obtain only pure carbon nanotube powder by removing the acid, metal salt compound, and oxidizing agent that may be added in the carbon nanotube dispersion. For this purpose, an excess of distilled water is added to the carbon nanotube into which the oxygen-containing functional group is introduced, washed, and the acid and metal salt compound are removed by filtering through a process such as centrifugation, thereby obtaining a purified carbon nanotube. The obtained carbon nanotube powder has dispersibility by introducing an oxygen-containing functional group from the carbon nanotube liquid crystal phase.

Then, the pretreated carbon nanotubes are dispersed in a solvent to prepare a carbon nanotube dispersion (S4).

A carbon nanotube dispersion solution can be prepared by dispersing the carbon nanotubes that have been pre-treated in one or more solvents of water (H ₂ O), dimethylformamide (DMF), and N-methylformamide (NMP). can

In particular, the pretreated carbon nanotube dispersion can be self-assembled in the form of a liquid crystal phase, which is a carbon nanotube liquid crystal phase having a structure in which a metal salt compound is co-intercalated between adjacent interlayers of carbon nanotubes through shear stress. As oxygen-containing functional groups are introduced into the carbon nanotubes through heat treatment, dispersibility of the carbon nanotubes in a solvent may be improved, and thus the carbon nanotubes may self-assemble.

Self-assembly refers to a process in which carbon nanotubes in a solvent form an organized structure as a result of specific local interactions between carbon nanotubes themselves without external influence. That is, the self-assembly is to form a new structure by spontaneously aligning the carbon nanotubes in the solvent, and the self-assembly of the carbon nanotubes is induced through the pretreatment as in the present invention, thereby increasing the dispersibility of the carbon nanotubes in the solvent. It means that it is formed in the same structure as the liquid crystal phase. If the pretreatment is not performed as in the present invention, the carbon nanotubes are dispersed in disordered and random directions in the solvent, and dispersion stability cannot be improved.

10 is a SEM photograph showing the carbon nanotube dispersion pretreated according to the present invention. Referring to FIG. 10, the carbon nanotube dispersion formed by redispersing pure carbon nanotube powder in a polar solvent was measured at 10.0 kV and enlarged at a magnification of 20,000 to represent a scanning electron microscope photograph, wherein the metal salt compound is the carbon nanotube. Since co-intercalation occurs between adjacent layers, it is confirmed that the self-assembled structure is formed in the form of a liquid crystal phase when formed as a carbon nanotube dispersion.

Unlike FIG. 10, FIG. 11 shows an SEM photograph of a carbon nanotube dispersion that has not been pretreated. Referring to FIG. 10, as a carbon nanotube dispersion prepared using a liquid crystal phase prepared by a general stirring method using a magnetic bar rather than a shear stress method in the liquid crystal phase manufacturing process, the carbon nanotubes are not self-assembled in the liquid crystal phase form It can be seen that they exist in a chaotic random direction.

Next, by spray-drying the mixed solution, as the solvent evaporates, the graphene oxide is coated to surround the silicon-based particles, and carbon nanotubes are bonded to the graphene oxide to prepare composite particles (S20).

As the solvent in the mixed solution evaporates with water through spray drying, a composite layer composed of a composite structure of graphene oxide and carbon nanotubes is coated on a single silicon-based particle or a plurality of silicon-based particles, thereby forming composite particles. At this time, since the mixed solution is in a state in which graphene oxide and carbon nanotubes are uniformly mixed with each other, graphene oxide may be coated on silicon-based particles in a state in which carbon nanotubes are embedded. That is, as the solvent evaporates during spray drying, small-sized graphene oxide and carbon nanotubes are coated on relatively large silicon-based particles by van der Waals force and some hydrogen bonds.

However, since the step of preparing the composite particles is before heat treatment in an air atmosphere, the carbon nanotubes may be carbon oxide nanotubes before reduction.

Finally, the composite particles are heat-treated to reduce graphene oxide and carbon nanotubes (S30).

It is heat-treated in an air atmosphere at 170 to 450° C. so that the carbon oxide nanotubes can be reduced while having a temperature range showing the thermal stability of high heat-resistant graphene oxide. Preferably, it can be heat-treated at 400° C. or lower in air, and it is also possible at 300° C. or lower.

In particular, since hydroxy among oxygen-containing functional groups may be introduced on the surfaces of graphene oxide and carbon oxide nanotubes, graphene oxide and carbon nanotubes may form a non-covalent bond with each other by hydrogen bonding. Accordingly, after the graphene oxide and carbon oxide nanotubes are reduced by heat-treating the composite particles, they are non-covalent due to the π-π interaction between the sp ² hexagonal structures (the attraction between the two when the molecules are adjacent to each other). bonding becomes possible.

The structure of the composite prepared by this process is confirmed through FIG. 12 schematically showing the composite for an anode material according to the present invention. That is, silicon-based particles 10 of any one or more of silicon, silicon alloy, and silicon oxide are positioned as a core, and high heat-resistance graphene 20 as a shell completely surrounding the outside of the silicon-based particles 10 is formed. At the same time as the coating, a portion of the carbon nanotubes 30 is embedded or embedded in the coated high heat-resistant graphene 20 and is formed.

Here, the high heat-resistant graphene constituting the composite is reduced to a graphene structure in which the high heat-resistant graphene oxide is removed from the surface of the epoxy group and the hydroxyl group at 200 to 250° C. or less to form an sp ² bond between carbon atoms while having conductivity As such, it has high-temperature heat resistance stability that is non-combustible at more than 250° C. and 450° C. or less, and in particular, the solid content at 400° C. in air may be 65 to 80% by weight.

However, in the present invention, the heat treatment for reducing graphene oxide and carbon oxide nanotubes is preferably performed in an air atmosphere, but in some cases chemical reduction, reduction in an inert gas, thermal reduction using plasma, Various reduction methods such as thermal reduction in hydrogen mixed gas may be applied.

According to the above-described manufacturing method, the present invention spray-drying a mixed solution containing high heat-resistant graphene oxide, silicon-based particles, carbon oxide nanotubes and a solvent to wrap high-heat-resistant graphene oxide on the outside of silicon-based particles, and high heat-resistant oxidation By preparing composite particles bonded in a state where a part of carbon oxide nanotubes are embedded on graphene, and heat-treating the composite particles prepared in this way at 170 to 450° C. in air, not in a high-temperature inert gas atmosphere, sp ³ bonding The high heat-resistant graphene oxide that was formed was reduced to a high heat-resistant graphene structure forming an sp ² bond, and the carbon oxide nanotube was reduced to a carbon nanotube, eventually resulting in a high heat-resistant graphene-silicon-carbon nanotube composite for anode material. can be synthesized.

As such, even without heat treatment in a high-temperature inert gas atmosphere, high heat-resistant graphene oxide and carbon oxide nanotubes are reduced to improve electrical conductivity, and thus, there is an advantage that can be applied to anode materials for secondary batteries.

Hereinafter, an embodiment of the present invention will be described in more detail as follows. However, the following examples are merely illustrative to help the understanding of the present invention, and the scope of the present invention is not limited thereby.

<Example 1> Preparation of high heat-resistant graphene oxide dispersion solution

First, a high heat-resistant graphene oxide dispersion solution for wet spinning was prepared as follows. 10 g of graphite and 75 g of sodium chlorate (NaClO ₃ ) were mixed in a powder state, and then 50 mL of fuming nitric acid was added in a small amount, and the oxidation process was performed at room temperature for 1 to 3 hours. Then, 1 L of distilled water was added to neutralize, 1 L of 1 M hydrochloric acid solution was added, and the process of centrifugation at 1,000 rpm was repeated twice to prepare purified graphite oxide. Then, it was peeled off with graphene oxide using an ultrasonic disperser under alkaline conditions by controlling the pH to 10 or higher with an ammonia solution. Then, distilled water was added and centrifuged to prepare an aqueous graphene oxide dispersion solution.

After freeze-drying the prepared graphene oxide dispersion solution and drying at 80° C., thermogravimetric analysis was performed, which was described above with graphene oxide prepared using the conventional potassium permanganate and sulfuric acid as in FIG. 6, and Examples 1, it was possible to confirm the thermal properties of the prepared graphene oxide. Existing graphene oxide shows a rapid mass decrease at 200° C. or less, but the high heat-resistant graphene oxide prepared by Example 1 is thermally reduced by removing the epoxy group and the hydroxyl group introduced to the graphene surface in the range of 200 to 350° C. was able to confirm

<Example 2> Preparation of carbon nanotube dispersion

A composite powder was prepared by mixing 5 g of single-walled carbon nanotubes and 5 g of nitrate in a powder state. A carbon nanotube liquid crystal phase was prepared by mixing the prepared composite powder and 1,000 ml of the sulfuric acid solution while stirring at 1,000 rpm for 40 minutes using a paste mixer capable of rotation and revolution. Then, the carbon nanotube liquid crystal phase was heated at 100° C. for 20 hours to introduce a carboxyl group to the carbon nanotube, and then washed with excess distilled water and centrifuged to obtain a pretreated carbon nanotube through filtering. A carbon nanotube dispersion liquid was prepared by dispersing the carbon nanotubes that had been pre-treated into powder in water and N-methylprollidone.

13 is a graph showing the thermal behavior of the carbon oxide nanotube according to Example 2, and at a temperature of 300° C. or less, a chemical functional group introduced to the end and surface of the carbon nanotube, that is, an oxygen-containing functional group is removed, so that water, CO ₂ , it was confirmed that gas was generated in the form of CO. As such, it was found that carbon oxide nanotubes, like graphene oxide, can be thermally reduced at a temperature of 300° C. or less, and furthermore, at a temperature of 250° C. or less.

<Example 3-1> Preparation of graphene oxide-silicon composites

A silicon alloy is mixed in water at 1 wt%, and 0.12 wt% of the high heat-resistant graphene oxide dispersion solution prepared in Example 1 is mixed, so that the silicon alloy is 1 wt% and the graphene oxide dispersion solution is 0.12 wt% was prepared. Silicon alloy microparticles coated with graphene oxide were prepared by using a spray dryer with the thus-prepared mixed solution. The prepared particles were treated in an oven at 300° C. in air to prepare reduced graphene-coated silicon alloy composite particles.

<Example 3-2> Preparation of high heat-resistance graphene-silicon-carbon nanotube composite

1 wt% of silicon alloy is mixed with water, and 1 wt% of silicon alloy is mixed with the high heat-resistant graphene oxide prepared in Example 1 and the single-walled carbon nanotube dispersion solution prepared in Example 2, and high heat-resistant graphene oxide A mixed solution was prepared so that the fins were 0.08% by weight and the single-walled carbon nanotubes were 0.04% by weight. Silicon alloy composite particles in which graphene oxide and single-walled carbon nanotubes were uniformly coated were prepared by using the thus-prepared mixed solution using a spray dryer. The prepared particles were treated in an oven at 300° C. in air to prepare silicon alloy composite particles coated with reduced graphene and bonded with single-walled carbon nanotubes.

14 is a SEM photograph of Example 3, FIG. 14A is a SEM photograph of the silicon alloy itself according to Examples 3-1 and 3-2, and FIG. 14B is an SEM photograph according to Example 3-1. The graphene oxide-coated silicon alloy composite particles are shown as an SEM photograph, and FIG. 14c is a SEM photograph of the silicon alloy composite particles coated with graphene oxide and single-walled carbon nanotubes according to Example 3-2, 14D is an enlarged SEM photograph of FIG. 14C.

With respect to Example 3-1, referring to FIG. 14b, it was confirmed that graphene was introduced to the surface of the silicon alloy particle. With respect to Example 3-2, referring to FIG. 14c , it was confirmed that graphene was introduced into the surface of the silicon alloy particle.

15 is a graph showing the thermogravimetric analysis (TGA) results of Example 3. Referring to FIG. 15 , it was confirmed that 6.1 wt% of graphene was introduced into the silicon alloy in Example 3-1 through thermogravimetric analysis. In addition, it was confirmed that the composite layer composed of 6.8 wt% of graphene and single-walled carbon nanotubes was coated on the surface of the silicon alloy particles in Example 3-2.

16 is a graph showing the results of Raman spectroscopy in Example 3. Referring to FIG. 16 , the presence of graphene and single-walled carbon nanotubes can be confirmed.

<Test Example 1>

In this test example, the characteristics of the negative electrode material according to the present invention when actually applied to a secondary battery were analyzed. For this, the high heat-resistant graphene-silicon-carbon nanotube composite prepared according to Example 3-2: carbon black (conductive material): polyacrylic acid (water-soluble binder) was mixed in an aqueous solution in a weight ratio of 8: 1: 1 to prepare a slurry, which was coated on a copper current collector to form a negative electrode layer, and then dried at 100° C. to remove moisture. Using the thus prepared electrode, a CR2032 standard coin cell was fabricated inside a glove box in an argon atmosphere. In this case, a lithium metal foil was used as the counter electrode. A polyolefin separator was interposed between both electrodes. 1M LiPF ₆ was used as the electrolyte, and a mixed solution of ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate was used as the solvent. Let this be sample A.

For comparative analysis, a slurry of the silicon alloy composite particles coated with reduced graphene according to Example 3-1 was prepared in the same manner as in Sample A, and then a battery sample was prepared. Let this be sample B.

In addition, a battery sample was prepared after preparing a slurry using the silicon alloy alone in the same manner as in Sample A. Let this be the C sample.

In addition, instead of the single-walled carbon nanotube used in Example 3-2, the high heat-resistance graphene-silicon-carbon nanotube composite prepared using the multi-walled carbon nanotube was prepared as a slurry in the same manner as in Sample A. After that, a battery sample was prepared. Let this be the D sample.

In this way, using the coin cells of each sample A, B, C, and D, the capacity retention rate and the coulombic efficiency compared to the charge/discharge cycle were measured, and the results are shown in FIGS. 17, 18 and 19 . That is, FIG. 17 is a graph showing the capacity retention rate according to the charge/discharge cycle of the electrode. In the case of sample C to which the silicon alloy alone is applied, the electrical conductivity is low and the volume changes during charging and discharging, so the capacity retention rate of only 4.7% after 50 repeated tests In the case of sample B, in which only graphene is complexed to a silicon alloy, a capacity retention rate of 74.7% after 50 repeated tests is shown, whereas in the case of sample A to which a high heat-resistance graphene-silicon-carbon nanotube composite is applied, the test is repeated 50 times. After that, it showed a significantly improved capacity retention rate of 89.5%.

In particular, in the case of using multi-walled carbon nanotubes with many defect structures, an improved effect was not obtained compared to the capacity retention rate of 74.7%, which is seen in the case of composite particles coated with a silicon alloy using high heat-resistant graphene oxide.

18 is a graph showing the coulombic efficiency according to the charge/discharge cycle of the electrode. Referring to FIG. 18 , in the case of sample A to which the high heat resistance graphene-silicon-carbon nanotube composite is applied, it can be confirmed that the high coulombic efficiency is maintained even after 50 repeated tests while showing a very high coulombic efficiency of 98.4% from the beginning.

19 is a graph showing the rate characteristics according to the charge/discharge cycle of the electrode. Referring to FIG. 19 , it can be confirmed that sample A to which the high heat-resistance graphene-silicon-carbon nanotube composite is applied exhibits high rate characteristics even at charge and discharge rates.

In summary, the present invention relates to a method for manufacturing a composite for an anode material including a pretreated carbon nanotube, and spray-drying a mixed solution containing graphene oxide, silicon-based particles, carbon nanotubes and a solvent to remove the silicon-based particles from the outside. It is characterized in that the graphene oxide and carbon nanotubes can be reduced through heat treatment that does not require a high-temperature inert gas atmosphere for composite particles in which graphene oxide and carbon nanotubes are combined.

As such, graphene oxide as in the present invention includes an oxygen-containing functional group that is an epoxy group or a hydroxy group on the surface, but does not have an oxygen-containing functional group that is a lactol group or a carboxyl group on the surface, so that it exhibits thermal stability. As graphene oxide with high heat resistance, It is meaningful in that heat treatment can be performed in an air atmosphere in a temperature range showing the thermal stability of high heat-resistant graphene oxide.

In addition, in the carbon nanotube as in the present invention, a shear stress is applied to a composite powder in which the carbon nanotube and a metal salt compound are mixed in a solid state and an acid solution, so that the metal salt compound is co-intercalated between adjacent interlayers of the carbon nanotube. After forming a liquid crystal phase of the carbon nanotube having a structure of It is meaningful in that an oxygen-containing functional group is introduced from the carbon nanotube liquid crystal phase to have dispersibility.

Therefore, according to the present invention, it is expected that the electrical conductivity of the anode material for a silicon-based secondary battery can be improved by the graphene oxide and carbon nanotubes, which can be reduced without heat treatment under a high temperature inert gas atmosphere because defects are minimized. do.

The above description is merely illustrative of the technical idea of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to illustrate, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

10: silicon-based particles
20: high heat resistance graphene
30: carbon nanotube
100: courage
R1: rotation axis
R2: orbital shaft

Claims (16)

Preparing a mixed solution containing graphene oxide, silicon-based particles, carbon nanotubes and a solvent;
preparing composite particles in which the graphene oxide is coated to surround the silicon-based particles as the solvent evaporates by spray-drying the mixed solution, and the carbon nanotubes are bonded to the graphene oxide; and
Reducing the graphene oxide and the carbon nanotubes by heat-treating the composite particles;
The carbon nanotubes are
A composite powder in which carbon nanotubes and a metal salt compound are mixed, and an acid solution are mixed while applying a shear stress to produce a carbon nanotube liquid crystal phase in which the metal salt compound is co-intercalated between adjacent layers of the carbon nanotubes to do;
heating the carbon nanotube liquid crystal phase to prepare a carbon nanotube into which an oxygen-containing functional group is introduced by the metal salt compound and an acid solution; and
Washing and filtering the carbon nanotube into which the oxygen-containing functional group is introduced; According to claim 1,
The graphene oxide includes an oxygen-containing functional group that is an epoxy group or a hydroxy group on the surface, but an oxygen-containing functional group that is a lactol group or a carboxyl group does not exist on the surface, so it is high heat-resistant graphene oxide showing thermal stability,
The heat treatment is a method of manufacturing a composite for a negative electrode material comprising a pretreated carbon nanotube, characterized in that made in a temperature range showing the thermal stability of the high heat-resistant graphene oxide. 3. The method of claim 2,
The graphene oxide is a high heat-resistant graphene oxide exhibiting thermal stability at 170 to 450 °C,
In the heat treatment of the composite particles, the method for producing a composite for a negative electrode material comprising a pretreated carbon nanotube, characterized in that the reduction by heat treatment of the high heat-resistant graphene oxide at 170 to 450 ℃. According to claim 1,
The graphene oxide is prepared by mixing graphite and a chlorate-based oxidizing agent in a powder state, adding concentrated nitric acid to oxidize the graphite oxide, and using a basic solution that does not contain metal ions, the graphite oxide in alkaline conditions of pH 10 or higher. A method for producing a composite for a negative electrode material comprising a pretreated carbon nanotube, characterized in that it is a high heat-resistant graphene oxide dispersion solution prepared by exfoliation. According to claim 1,
The silicon-based particles, but any one or more of silicon, silicon alloy and silicon oxide,
Metal elements included in the silicon alloy are Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re , Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb , Bi, S, Se, Te, and a method of manufacturing a composite for a negative electrode material comprising a pretreated carbon nanotube, characterized in that at least one selected from the group consisting of. According to claim 1,
The carbon nanotube is prepared by further comprising; dispersing the pretreated carbon nanotube in a solvent to prepare a carbon nanotube dispersion;
A method of manufacturing a composite for a negative electrode material comprising a pretreated carbon nanotube, characterized in that the pretreated carbon nanotube dispersion can be self-assembled in a liquid crystal form. According to claim 1,
The carbon nanotube, single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (double-walled carbon nanotube, DWCNT) and multi-walled carbon nanotube (multi-walled carbon nanotube, MWCNT) of A method of manufacturing a composite for an anode material comprising a pretreated carbon nanotube, characterized in that at least one. According to claim 1,
The metal salt compound is any one or more of nitrate, sulfate and phosphate,
The nitrate is at least one selected from the group consisting of sodium nitrate (NaNO ₃ ), potassium nitrate (KNO ₃ ) and calcium nitrate (Ca(NO ₃ ) ₂ ),
The sulfate is at least one selected from the group consisting of sodium sulfate (Na ₂ SO ₄ ), potassium sulfate (K ₂ SO ₄ ), sodium hydrogen sulfate (NaHSO ₄ ) and potassium hydrogen sulfate (KHSO ₄ ),
The phosphate is dipotassium phosphate (K ₂ HPO ₄ ) and potassium phosphate (KH ₂ PO ₄ ) Method for producing a composite for a negative electrode material comprising a pretreated carbon nanotube, characterized in that at least one selected from the group consisting of . According to claim 1,
In the step of preparing the liquid crystal phase, the method for producing a composite for a negative electrode material comprising pretreated carbon nanotubes, characterized in that the shear stress is applied by stirring for 30 minutes to 3 hours at a rotation speed of 100 to 2,000 rpm . According to claim 1,
The preparing of the liquid crystal phase comprises applying the shear stress using any one or more of an impeller, a paste mixer, and a Kuett-Tayler reactor. Way. According to claim 1,
The preparing of the liquid crystal phase comprises applying the shear stress using any one or more of an impeller, a paste mixer, and a Kuett-Tayler reactor. Way. According to claim 1,
The step of preparing the liquid crystal phase comprises mixing the carbon nanotubes and the metal salt compound in a weight ratio of 1:0.1 to 10 to form a composite powder. manufacturing method. According to claim 1,
The preparing of the carbon nanotube into which the oxygen-containing functional group is introduced is a method of manufacturing a composite for a negative electrode material including a pretreated carbon nanotube, characterized in that the liquid crystal phase is heated at 25 to 150°C. According to claim 1,
In the step of preparing the carbon nanotube into which the oxygen-containing functional group is introduced, an oxidizing agent is further added to the liquid crystal phase and stirred, and then the liquid crystal phase is heated to prepare the carbon nanotube into which the oxygen-containing functional group is introduced. A method of manufacturing a composite for an anode material comprising a pretreated carbon nanotube. A composite prepared by the method of any one of claims 1 to 14. anode;
A negative electrode comprising the composite according to claim 15;
a separator provided between the anode and the cathode; and
A secondary battery comprising; an electrolyte.

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