WO2015199251A1 - Nanoparticle-graphene-carbon composite having graphene network formed therein, preparation method therefor and application thereof - Google Patents

Abstract

The present invention relates to a nanoparticle-graphene-carbon composite having a graphene network formed therein and, more specifically, to an electrode using a nanoparticle-graphene-carbon composite having a graphene network formed therein by dispersing graphene between nanoparticles coated with carbon within the composite, a secondary battery comprising the same, and an electric power storage apparatus comprising the same. The nanoparticle-graphene-carbon composite according to the present invention includes graphene having excellent conductivity and mechanical elasticity and a remarkably large specific surface area, which is uniformly dispersed within the composite, thereby absorbing changes in volume according to charging/discharging, and forming an electrically conductive network within the composite, and thus can be used as an electrode material of a secondary battery having high capacity and a remarkably extended cycle lifespan. In particular, the preparation method of the present invention allows easy mass-production by a sol-gel method.

Description

Nanoparticle-graphene-carbon composites with graphene networks formed therein, methods for their preparation and applications thereof

The present invention relates to a nanoparticle-graphene-carbon composite in which a graphene network is formed therein. Specifically, graphene is dispersed between nanoparticles in the composite, and thus, nanoparticle-graphene-carbon in which a graphene network is formed. An electrode using the composite, and a secondary battery and a power storage device including the same.

Lithium secondary batteries are becoming more important as a power source for portable electronic devices, as well as non-IT power sources such as hybrid cars, plug-in hybrid cars and electric vehicles, and industrial tools and robots. In addition, it is expected to expand its use as a large-capacity energy storage device to improve the power quality due to the intermittent power generation for the widespread distribution of renewable energy such as solar and wind power generation.

Therefore, the performance of the lithium secondary battery is very important for the application of the lithium secondary battery, and compared with the performance of the conventional lithium secondary battery, the storage capacity (active material unit weight or charging capacity per unit volume), output (active material unit weight or discharge rate per unit volume), There is an increasing demand for the development of lithium secondary batteries with improved stability and lifespan (repetitive charge / discharge times while maintaining storage capacity). This property is primarily determined by the properties of the electrode active material used as the electrode material.

Graphite is used as a negative electrode material of a conventional lithium secondary battery, but the maximum storage theoretical capacity is about 372 mAh / g, and the theoretical capacity of the lithium secondary battery is recently exhibited in commercial lithium secondary batteries. In addition, new cathode materials with higher storage capacity than conventional cathode materials are being developed for lithium secondary batteries. Therefore, in order to increase the energy storage capacity of the lithium secondary battery, a negative electrode material having a higher storage capacity than graphite should be developed. Among the candidate materials for lithium secondary batteries that can replace graphite, a group of metals (Si, Sn, As, Ge, Bi, Al, In, Pb, and Ga) that react with lithium electrochemically to form an alloy is of interest. Is dragging. In particular, since silicon has high theoretical capacity (~ 4200 mAh / g), low charge potential (~ 0.2 V vs Li / Li ⁺ ), and is an eco-friendly and abundant resource, much research has been conducted to develop high capacity negative electrode material for next generation lithium secondary battery. ought. However, due to the large volume change (> 300%) that occurs when lithium ions are charged / discharged, polarization and cracking of electrodes occur, and the resulting silicon surface reacts with a new solid-electrolyte-bound layer (solid electrolyte interface). , SEI) is continuously generated to increase the internal resistance has a problem of low efficiency and reduced capacity during cycle repetition, shortening the lifespan. In addition, silicon has a very low electrical conductivity, so a method of manufacturing a conductive material and a composite form is needed.

In order to solve these problems, a method of manufacturing a conductive material including a carbon material and a silicon composite material has been attempted. Among them, a method of coating a silicon structure material with carbon is used as the most typical method. For this purpose, resorcinol-formaldehyde (RF) gel, glucose, high temperature heat treated carbon black, citric acid, polyvinylidene fluoride (PVDF), sucrose Various carbon coating raw materials such as sucrose have been used. However, although the cycle stability is relatively improved by coating the silicon structure material with a carbon material, there is still a problem that the capacity reduction is not completely overcome by the large volume change due to repeated charge / discharge cycles.

Meanwhile, graphene among carbon materials can be mass-produced through chemical oxidation, exfoliation process, and chemical or thermal reduction treatment using natural and synthetic graphite which is rich and cheap. (WS Hummers and RE Offeman, J. Am. Chem. Soc. 1958, 80, 1339; NI Kovtyukhova, PJ Ollivier, BR Martin, TE Mallouk, SA Chizhik, EV Buzaneva, and AD Gorchinskiy, Chem. Mater. 1999 , 11, 771). Graphene is structurally and chemically very stable by strong sp ² bonds between carbon atoms, has high thermal conductivity, and has very good electrical conductivity. In particular, the mechanical strength is more than 200 times stronger than steel, and the hexagonal honeycomb structure allows for a large amount of space, flexibility, and excellent mechanical elasticity. It has a high specific surface area of 2600 m ² / g. Recently, an example of using the graphene material as an additive for an existing electrode active material or forming a composite with a heterogeneous compound as an electrode material for a lithium secondary battery has been reported. This is done to complement the lacking characteristics of the existing electrode material or to induce synergistic effect with the heterogeneous compound property by complexing with the heterogeneous compound.To date, the material used as graphene and the composite material is largely doped with metal. Or composites, composites with carbon or polymer materials, composites with metal oxides, and ceramic composites.

Accordingly, the present inventors have made efforts to develop an electrode material having a high capacity and a long cycle life while solving the reduction of capacity due to the repeated charge / discharge cycles. By forming a composite using graphene having conductivity, it was confirmed that the material exhibits excellent properties as an electrode material, and the present invention was completed.

Accordingly, the present invention provides a nanoparticle-graphene-carbon composite in which a graphene network is formed therein.

In another aspect, the present invention provides a method for producing a nanoparticle-graphene-carbon composite in which a graphene network is formed.

In addition, the present invention is to provide an electrode for a secondary battery using a nanoparticle-graphene-carbon composite having a graphene network formed therein as a problem.

Another object of the present invention is to provide a secondary battery including the secondary battery electrode and the electrolyte, and an electronic device and a power storage device including the secondary battery as a power supply source.

The present invention for solving the above problems, as one aspect, metal nanoparticles reacting with lithium; Carbon coated on the outside of the nanoparticles; And a graphene forming a uniform network among the nanoparticles. The graphene provides a nanoparticle-graphene-carbon composite having a graphene network formed therein.

In another aspect, the present invention to solve the other problem, the step of forming a composite gel by adding a carbon precursor to an aqueous solution containing a metal nanoparticle and a graphene oxide to react with lithium; And heat treating the composite gel. The method provides a method of manufacturing a nanoparticle-graphene-carbon composite having a graphene network formed therein.

In accordance with another aspect, the present invention provides a secondary battery electrode including a current collector coated with a nanoparticle-graphene-carbon composite having graphene dispersed therein.

In another aspect, the present invention provides a secondary battery including the secondary battery electrode and the electrolyte.

In accordance with another aspect of the present invention, there is provided a power storage device and an electronic device including the secondary battery as a power supply source.

In the nanoparticle-graphene-carbon composite according to the present invention, a small amount of graphene is dispersed therein, so that the nanoparticles generate electrical energy through an electrochemical reaction with lithium, and between the nanoparticles coated with carbon. The graphene forms a uniform network, and the graphene forming the network has an effect of absorbing the volume change occurring during the charging / discharging process and providing a conductive passage.

In addition, the composite according to the present invention, by increasing the conductivity while preventing the aggregation between the nanoparticles by the electrochemical reaction of the carbon material and graphene coated with the nanoparticles can be utilized as an excellent electrode material high capacity and cycle There is an effect that can provide a secondary battery having a very long life.

In addition, according to the method for preparing a composite according to the present invention, while forming a composite by the sol-gel method, a small amount of graphene may be evenly dispersed by adding a small amount of graphene oxide. It is dispersed and able to produce a large amount of nanoparticle-graphene-carbon composite having a graphene network therein.

1 shows a manufacturing process chart of the nanoparticle-graphene-carbon composite having a graphene network formed therein according to the present invention, process A is prepared according to Examples 1 to 3 using sodium carbonate as a catalyst for forming a composite gel. Process B, Process B shows a manufacturing process according to Examples 4 to 5 using ammonium hydroxide as a catalyst for forming a complex gel. When ammonium hydroxide is used as a catalyst for forming the composite gel, the composite may be manufactured by heat treatment after direct drying without washing.

FIG. 2 schematically illustrates a mechanism for preparing a nanoparticle-graphene-carbon composite having a graphene network formed therein according to an embodiment of the present invention.

Figure 3a is a functional effect on the electrode using a nanoparticle-graphene-carbon composite having a graphene network therein in accordance with the present invention, Figure 3b is an electrode using a nanoparticle-carbon composite containing no graphene It is a schematic diagram showing the effect.

4 to 6 show transmission electron microscope (TEM) images of silicon-graphene-carbon composites having graphene networks formed therein prepared by Examples 1 to 3 of the present invention.

FIG. 7 shows a transmission electron microscope (TEM) photograph of a silicon-graphene-carbon composite having a graphene network formed therein according to Example 5 of the present invention.

Figure 8 shows a TEM picture of the silicon-carbon composite containing no graphene prepared by Comparative Example 1 of the present invention.

9 is a silicon-graphene-carbon composite having a graphene network formed therein according to Example 2 of the present invention (a, b), a silicon-graphene-carbon composite having a graphene network formed therein according to Example 5 SEM images of the silicon-carbon composites (e, f) of (c, d) and Comparative Example 1 are shown.

10 is a graph showing the results of X-ray diffraction (XRD) analysis of the silicon-graphene-carbon composites prepared by Examples 1 to 5 of the present invention and the silicon-carbon composites prepared by Comparative Example 1. FIG. (a: Examples 1 to 3 and Comparative Examples 1 and b: Examples 4 to 5)

11 is a thermogravimetric analysis (TGA) of a silicon-graphene-carbon composite and a silicon-carbon composite according to Comparative Example 1 having a graphene network formed therein prepared by Examples 1 to 5 of the present invention. A graph showing the results. (a: Example 1, b: Example 2, c: Example 3, d: Example 4, e: Example 5, f: Comparative Example 1)

12 is a lithium secondary battery (lithium metal prepared by using the silicon-graphene-carbon composites prepared by Examples 1 to 3 of the present invention, and the silicon-carbon composite prepared by Comparative Example 1 as an electrode active material It is a graph showing the charge / discharge cycle performance of a half cell made of a standard electrode.

FIG. 13 shows the charging / recharging of a lithium secondary battery (half cell made of lithium metal as a standard electrode) manufactured using the silicon-graphene-carbon composite prepared according to Example 2 of the present invention as an electrode active material. A graph showing discharge cycle performance.

14 is a view of a lithium secondary battery (half cell made of lithium metal as a standard electrode) manufactured by using the silicon-graphene-carbon composite prepared according to Examples 4 to 5 of the present invention as an electrode active material. Graph showing charge / discharge cycle performance.

15 is a lithium secondary battery prepared using a silicon-graphene-carbon composite prepared in Example 2 of the present invention as a negative electrode active material and a Ni-rich NCM positive electrode active material (full lithium secondary battery, full cell) Is a graph showing the charge / discharge voltage and cycle performance. (a: charge / discharge voltage, b: charge / discharge cycle performance).

Hereinafter, the present invention will be described in detail.

The present invention in one aspect,

Metal nanoparticles reacting with lithium; Carbon coated on the outside of the nanoparticles; And a graphene forming a uniform network among the nanoparticles. The present invention relates to a nanoparticle-graphene-carbon composite having a graphene network formed therein.

In the composite of the present invention, graphene having excellent mechanical properties and excellent electrical conductivity is dispersed in the composite, and forms a network between the carbon-coated metal nanoparticles, thereby repeating the charge / discharge cycle. In the event of detachment / cracking of the electrode, the conductive network can be maintained by the graphene to enable reversible charging / discharging, thereby exhibiting excellent characteristics as an electrode material.

At this time, preferably the metal nanoparticles are characterized in that it comprises 20 to 80% by weight of the total weight of the composite.

Also preferably, the metal nanoparticles are Si, Sn, As, Ge, Bi, Al, In, Pb, and Ga, which are nanoparticles having a high storage capacity and a large volume change upon repeated electrochemical charge / discharge with lithium. It is characterized in that the selected one metal nanoparticles or a mixture of one or more metal nanoparticles.

Also preferably the nanoparticles are characterized in that the size of 1 ~ 200 nm.

In the nanoparticle-graphene-carbon composite of the present invention, after dispersing the metal nanoparticles and graphene oxide in water, a carbon precursor and a catalyst are added to form a graphene oxide composite gel, and graphene is subjected to carbonization heat treatment. Evenly dispersed in the composite to form a network between the carbon-coated nanoparticles, it is prepared to form a graphene network inside the composite (see FIGS. 1 and 2).

Therefore, as another embodiment of the present invention, the method comprising: forming a composite gel by adding a carbon precursor to the aqueous solution containing the metal nanoparticles and the graphene oxide to react with lithium; And heat treating the composite gel. Provided is a method of manufacturing a nanoparticle-graphene-carbon composite having a graphene network formed therein.

According to the present invention by forming a complex by the sol-gel method by adding a small amount of graphene oxide evenly dispersed in the graphene inside the composite, to prepare a nanoparticle-graphene-carbon composite having a graphene network therein It becomes possible. That is, in the present invention, the metal nanoparticles and the graphene oxide are dispersed in water by using a graphene oxide that is particularly water-soluble, and then the graphene oxide is mixed by adding a carbon precursor having a chemical functional group similar to the graphene oxide. After forming a composite gel while improving the properties and undergoing a heat treatment, as a result, it is possible to prepare a composite of nanoparticles-graphene-carbon in which graphene forms a network inside the composite.

Preferably, the graphene oxide is characterized in that it comprises 0.05 to 2.0% by weight relative to the weight of the total raw material to form a composite gel.

Also preferably, the metal nanoparticles are Si, Sn, As, Ge, Bi, Al, In, Pb, and Ga, which are nanoparticles having a high storage capacity and a large volume change upon repeated electrochemical charge / discharge with lithium. It is characterized in that the selected one metal nanoparticles or a mixture of one or more metal nanoparticles.

Also preferably, the metal nanoparticles are characterized in that the average particle diameter of 1 ~ 200 nm size. If the average particle diameter is smaller than the lower limit of the metal nanoparticles, it is difficult to evenly disperse the inside of the composite, and if larger than the upper limit, the cycle life may be shortened due to the large volume change.

Also preferably, the carbon precursor is at least one mixture selected from resorcinol-formaldehyde, phenol-formaldehyde or perperyl alcohol.

Also preferably, the catalyst is characterized in that one or more mixtures selected from sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, ammonium chloride or ammonium hydroxide. When ammonium hydroxide is used, the manufacturing process may be simplified since the complex manufacturing process does not include a washing process.

Also preferably, the complex gel is formed at a temperature of 60 to 90 ° C. in a closed reactor.

Also preferably, the heat treatment is performed at an inert gas or a mixed gas atmosphere of inert gas and hydrogen at a temperature range of 600 to 1000 ° C.

In still another aspect, the present invention relates to a secondary battery electrode comprising a current collector coated with a nanoparticle-graphene-carbon composite having a graphene network formed therein, the composite according to the present invention. Graphene with excellent conductivity and mechanical elasticity and very large specific surface area is evenly distributed inside, so it is easy to absorb volume change even during repeated long-term charging / discharging with large volume change. It is to provide a secondary battery electrode having a high capacity and a remarkably long cycle life. In this case, preferably, the current collector is coated with the nanoparticle-graphene-carbon composite using PVA (Poly vinyl acetate) or PAA (Poly acrylic acid) or CMC (Carboxymethyl Cellulose) as a polymer binder. do.

Accordingly, the present invention is another embodiment, the secondary battery electrode including a current collector, the nanoparticle-graphene-carbon composite with a graphene dispersed therein, which is a secondary battery electrode having a high capacity and a remarkably long cycle life. A secondary battery comprising an electrode and an electrolyte. Preferably the electrolyte is characterized in that it comprises 2 to 20vol% of fluoroethylene carbonate or vinylene carbonate.

In still another aspect, the present invention relates to a power storage device and an electronic device including the secondary battery as a power supply source.

Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

<Production of Graphene Oxide>

Graphene oxide (graphene oxide) used in the present invention as a raw material of graphite powder (Asbury Carbons, 230U Grade, High Carbon Natural Graphite 99+) reported by Kovtyukhova et al. (NI Kovtyukhova) , PJ Ollivier, BR Martin, TE Mallouk, SA Chizhik, EV Buzaneva, and AD Gorchinskiy, Chem. Mater. 1999, 11, 771), by the modified Hummers method.

That is, in the first oxidation process, the graphite powder (2 g) was dissolved in potassium persulfate (K ₂ S ₂ O ₈ , 1.0 g) and phosphorus pentoxide (P ₂ O ₅ , 1.0 g) at 80 ° C. sulfuric acid solution (20 mL ) Was added to the beaker with stirring with stirring. The mixture was maintained at 80 ° C. for 4.5 hours, then cooled to room temperature and diluted in 1 L of distilled water. The pretreated product was filtered through a filter and washed until the pH of the water passed through the filter was neutral. The filtered product was dried in air overnight and the dried product was dispersed with stirring in cooled sulfuric acid solution (75 mL) in an ice vessel. Potassium permanganate (KMnO ₄ , 10 g) is slowly added thereto while stirring, so that the temperature rise due to the reaction heat is 20 ° C. or less. Thereafter, the dark green mixture was left at 35 ° C. for 2 hours, and distilled water (160 mL) was added to obtain a dark brown mixture. When distilled water was added, the temperature of the mixture was kept below 50 ° C. while distilled water was added in small portions to prevent foam formation due to exotherm. The mixture to which distilled water was added was further stirred for 2 hours, followed by dilution with distilled water (500 mL), and hydrogen peroxide (H ₂ O ₂ , 30%, 8.3 mL) was slowly added thereto to obtain a light yellow mixture. After the mixture was precipitated overnight, the upper solution was removed and 10% aqueous hydrochloric acid (HCl) solution (800 mL) was added to the remaining precipitate to give a brown mixture which was stirred for 3-5 hours. After that, it is allowed to settle overnight and the supernatant is removed. The remaining precipitate is washed with distilled water using a centrifuge and repeated until the pH of the wash solution is neutral. The obtained graphene oxide was diluted in distilled water and stored in a place where the light is blocked. In the subsequent use, by dispersing with ultrasonic waves for about 1 hour to form a uniform graphene oxide concentration, the concentration was measured and used to collect the required amount.

<Example 1> Preparation of silicon-graphene-carbon composite 1

A small amount of graphene oxide and silicon nanoparticles (KCC, average particle size of 10 ~ 50 nm) prepared above were put in distilled water and completely dispersed by ultrasonic vibration. Resorcinol and formaldehyde were dissolved in distilled water in which graphene oxide and silicon nanoparticles were completely dispersed, and then dissolved at room temperature. A small amount of sodium carbonate standard solution (0.2M Na ₂ CO ₃ aqueous solution) was added as a catalyst. . At this time, the content of graphene oxide in the total mixture is 0.08 wt%. The mixture was placed in a fully sealed reactor and stirred until a gel was produced in the temperature range of 70-90 ° C. And the carbon gel containing the graphene oxide and silicon nanoparticles obtained by this reaction was maintained for an additional 16 hours at 90 ℃. Thereafter, the obtained composite gel was washed repeatedly with distilled water to remove the catalyst, and the solvent was exchanged with isopropyl alcohol. Dried overnight in a dryer at 80 ℃, put the dried gel in a crucible into a tubular furnace, heat-treated for 2 hours at 850 ℃ in an argon gas atmosphere and then naturally cooled.

Example 2 Preparation of Silicon-Graphene-Carbon Composites 2

In this example, a silicon-graphene-carbon composite was prepared in the same manner as in Example 1 except that the content of graphene oxide was 0.37 wt%.

Example 3 Preparation of Silicon-Graphene-Carbon Composites 3

In this example, a silicon-graphene-carbon composite was prepared in the same manner as in Example 1 except that the graphene oxide content was 0.88 wt%.

Example 4 Preparation of Silicon-Graphene-Carbon Composites 4

A small amount of graphene oxide prepared above and silicon nanoparticles (KCC, average particle size of 10 to 50 nm) were put in distilled water and completely dispersed by ultrasonic vibration. Resorcinol and formaldehyde were dissolved in distilled water in which graphene oxide and silicon nanoparticles were completely dispersed, and then dissolved at room temperature. A small amount of aqueous ammonium hydroxide solution (0.5 wt% NH ₄ OH) was added as a catalyst. At this time, the content of graphene oxide in the total mixture is 0.1 wt%. The mixture was placed in a fully sealed reactor and stirred until a gel was produced in the temperature range of 70-90 ° C. And the carbon gel containing the graphene oxide and silicon nanoparticles obtained by this reaction was maintained for an additional 16 hours at 90 ℃. Thereafter, the obtained composite gel was dried overnight in a dryer at 80 ° C., and the obtained gel was placed in a crucible, placed in a tubular furnace, heat-treated at 850 ° C. for 2 hours in an argon gas atmosphere, and then naturally cooled.

Example 5 Preparation of Silicon-Graphene-Carbon Composites 5

In this example, a silicon-graphene-carbon composite was prepared in the same manner as in Example 4, except that the amounts of carbon precursors resorcinol, formaldehyde, and an aqueous ammonium hydroxide solution were different (see Table 1). .

Comparative Example 1 Preparation of Silicon-Carbon Composite

Silicon nanoparticles (KCC Co., Ltd., average particle size 10-50 nm) were put into distilled water, and it disperse | distributed completely by the ultrasonic vibration. Resorcinol and formaldehyde were dissolved in distilled water in which silicon nanoparticles were completely dispersed, and then dissolved at room temperature. Then, sodium carbonate standard solution (0.2 M Na ₂ CO ₃ aqueous solution) was added as a catalyst. The mixture was placed in a fully sealed reactor and stirred until a gel was produced in the temperature range of 70-90 ° C. Then, when the carbon gel containing silicon nanoparticles is formed it was maintained for an additional 16 hours at 90 ℃. The obtained composite gel was washed repeatedly with distilled water to remove the catalyst, and the solvent was replaced with isopropyl alcohol. The gel was dried overnight at 80 ° C., placed in an alumina crucible, placed in a tubular furnace, heat-treated at 850 ° C. for 2 hours in an argon gas atmosphere, and then naturally cooled to prepare a silicon-carbon composite including silicon.

The compositions of the raw materials used in the preparation of Examples 1 to 5 and Comparative Example 1 are shown in Table 1 below.

Table 1 Raw material (unit) Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Silicon nanoparticles (g) 0.28 0.35 0.40 0.35 0.35 0.28 Resorcinol (g) 0.65 0.76 0.79 0.81 0.54 0.66 Formaldehyde (g) 0.39 0.47 0.51 0.49 0.32 0.40 0.2 M aqueous sodium carbonate solution (mL) 0.59 0.69 0.71 - - 0.60 0.5 wt% NH ₄ OH aqueous solution (mL) - - - 0.16 0.10 - Graphene oxide (g) 0.02 0.10 0.25 0.02 0.02 - Distilled Water (mL) 21.23 24.73 25.69 18.94 18.94 20.32 Gross weight (g) 23.15 27.10 28.35 20.77 20.27 22.25 Graphene Oxide Content (wt%) 0.08 0.37 0.88 0.10 0.10 0.00

<Physical and Chemical Characterization of Prepared Complexes>

The physical and chemical properties of the composites prepared in Examples 1 to 5 and Comparative Example 1 were analyzed. At this time, the particle size and structure were determined by transmission electron microscope (TEM) (JEOL JEM-2010, 200.0kV) and X-ray diffraction (XRD) (Rigaku model D / MAX-50kV, Cu). -K radiation, = 1.5418). The silicon content of the prepared composite was analyzed by a method of increasing the temperature to 10 / min up to 800 under air flow using thermogravimetric analysis (TGA).

 TEM analysis results of the silicon-graphene-carbon composite prepared in Example 1 are shown in FIG. 4. Referring to FIG. 4, it can be seen that carbon surrounds the silicon particles, and the silicon nanoparticles coated with carbon are in intimate contact with the expanded graphene surface. XRD analysis (FIG. 10A) revealed diffraction peaks of silicon crystals (peaks at 2θ = 28.3 °, 47.2 ° and 56.1 ° correspond to Si (111), (220), and (311) planes, respectively). Graphite crystal peaks (2θ = 26.4 °) which appeared when graphene was layered were not observed. This indicates that a small amount of graphene is evenly dispersed within the composite. As a result of TGA analysis (FIG. 11A), the silicon content was 45 wt% and the total carbon content including graphene was 55 wt%.

  TEM analysis results of the silicon-graphene-carbon composite prepared in Example 2 are shown in FIG. 5. Referring to FIG. 5, the silicon nanoparticles were coated with carbon, and graphene dispersed well around the silicon / carbon particles was clearly observed. In addition, SEM results are shown in FIGS. 9A and 9B, and it can be clearly seen that graphene forms a network with carbon nanoparticles coated with carbon in the composite. XRD analysis (FIG. 10A) revealed diffraction peaks of silicon crystals (peaks at 2θ = 28.3 °, 47.2 ° and 56.1 ° correspond to Si (111), (220), and (311) planes, respectively). Graphite crystal peaks (2θ = 26.4 °) were observed when graphene was layered, and it was confirmed that graphene was evenly dispersed in the composite material. As a result of TGA analysis (FIG. 11B), the silicon content was 46 wt% and the total carbon content including graphene was 54 wt%.

TEM analysis results of the silicon-graphene-carbon composite prepared in Example 3 are shown in FIG. 6. Referring to FIG. 6, it can be seen that carbon surrounds silicon particles and silicon is well dispersed within carbon. It can also be seen that the carbon coated silicon particles are in intimate contact with the wide graphene plane. XRD analysis (FIG. 10A) revealed diffraction peaks of silicon crystals (peaks at 2θ = 28.3 °, 47.2 ° and 56.1 ° correspond to Si (111), (220), and (311) planes, respectively). Graphite crystal peaks (2θ = 26.4 °) that appear when the graphene layered were not observed, indicating that the graphene was evenly dispersed within the composite. As a result of TGA analysis (FIG. 11C), the silicon content was 46 wt% and the total carbon content including graphene was 54 wt%.

In addition, in Examples 4 and 5, resorcinol and formaldehyde were added as carbon precursors to the silicon nanoparticles and the graphene oxide dispersion solution, and a small amount of ammonium hydroxide was used as the complex gel formation catalyst. 1), by using ammonium hydroxide as a catalyst, the ammonium hydroxide catalyst was easily removed during the heat treatment of the composite gel to form a silicon-graphene-carbon composite in which a graphene network was formed without a separate washing process.

XRD analysis results of the silicon-graphene-carbon composite prepared in Example 4 (FIG. 10b), diffraction peaks (2θ = 28.3 °, 47.2 ° and 56.1 ° peaks of silicon crystals were Si (111), ( 220), and (311) plane), but the graphite crystal peaks (2θ = 26.4 °) when graphene is layered are not observed. It can be seen that it is dispersed. As a result of TGA analysis (FIG. 11D), the content of silicon was 43.5 wt% and the total carbon content including graphene was 56.5 wt%.

In addition, the TEM analysis results of the silicon-graphene-carbon composite prepared in Example 5 are shown in FIG. 7. Referring to Figure 7, it can be seen that the silicon particles coated with carbon are present in the vicinity of the graphene. As shown in the SEM analysis results in FIGS. 9c and d, carbon coated silicon particles were observed, and a graphene layer was observed between the particles, indicating that a graphene network was formed inside the composite. That is, in the case of using ammonium hydroxide as a catalyst, the process of the manufacturing process is omitted, thereby simplifying the process, but forming a silicon-graphene-carbon composite in which a graphene network is formed inside the same structure as in Examples 1 to 3. It could be confirmed. XRD analysis (FIG. 10b) revealed diffraction peaks of silicon crystals (peaks at 2θ = 28.3 °, 47.2 °, and 56.1 ° corresponding to Si (111), (220), and (311) planes, respectively). Graphite crystal peaks (2θ = 26.4 °) that appear when the graphene layered were not observed, indicating that the graphene was evenly dispersed within the composite. As a result of TGA analysis (FIG. 11e), the silicon content was 52.2 wt% and the total carbon content including graphene was 47.8 wt%.

TEM analysis results of the silicon-carbon composite not including graphene prepared in Comparative Example 1 are shown in FIG. 8. Referring to FIG. 8, it can be seen that the silicon is evenly dispersed in the carbon, and the carbon is surrounded by the silicon particles having the size of 10 to 50 nm. 9E and f show SEM results, and the composite shows a shape in which silicon nanoparticles coated with carbon are aggregated. XRD analysis (FIG. 10A) shows diffraction peaks of silicon crystals (peaks at 2θ = 28.3 °, 47.2 ° and 56.1 ° correspond to Si (111), (220), and (311) planes, respectively). . TGA analysis of the silicon-carbon composite in the air atmosphere (FIG. 11F) showed that the silicon content was 44 wt% and the carbon content was 56 wt%.

Preparation Example 1 Fabrication of Lithium Secondary Battery

Composites prepared in Examples 1 to 5 and Comparative Example 1 as electrode active materials, carbon black as a conductive material, and 5 wt% solution dissolved in polyvinyl acetate, DMSO (dimethyl sulfoxide) as a polymer binder Mixing was performed at a weight ratio of 80:10:10 to obtain a slurry mixture. The slurry was applied at 45 μm on a thin copper plate current collector having a thickness of 9 μm, dried at 80 ° C. for 2 hours, and compressed into 36 μm in a compressor. Then, after vacuum drying overnight at 80 ℃, cut to 1.54cm ² to prepare an electrode.

In the argon glove box, the composite working electrode and the lithium metal reference electrode were stacked in a 2016 coin cell, and a 2.54 cm ² polypropylene (PP) separator was interposed therebetween, and ethylene carbonate (ethylene carbonoate) and dimethyl carbonate ( dimethyl carbonate) and fluoroethylene carbonate in which 1.3M LiPF ₆ is dissolved in an electrolyte solution in which 1.0M LiPF ₆ is dissolved in a solution containing 30:40:30 in a volume ratio of 30:40:30. Was injected to produce a lithium secondary battery. At this time, the content of phloethylene carbonate in the total electrolyte was set to 10 vol%.

Lithium secondary battery (half cell) Analysis of Electrochemical Properties of

In order to analyze the electrochemical characteristics of the manufactured lithium secondary battery, charge / discharge cycle characteristics were analyzed by a constant current method in a voltage range of 0.02 to 1.5V. In order to analyze the electrochemical characteristics of the prepared composite electrode active material, the charge / discharge cycle characteristics were analyzed at various current densities based on the electrode active material in a voltage range of 0.02 to 1.5V.

12 shows the results of analyzing the charge / discharge cycle characteristics of the composites prepared in Examples 1 to 3 and Comparative Example 1 as the electrode active material, the initial three cycles at a current density of 100 mA / g, After 100 cycles, the charge / discharge cycles were analyzed under the current density of 500 mA / g.

Referring to FIG. 12, Example 1 contains a very small amount of graphene oxide, which is used in the total raw material mass of the electrode active material composite, at 0.08 wt%, at an initial three cycles at a current density of 100 mA / g. The charging capacity ranged from 680 to 700 mAh / g, and then the capacity retention rate was about 420 mAh / g until 100 cycles after the charging capacity was gradually reduced to 465 mAh / g up to 10 cycles under severe current density of 500 mA / g. Indicated.

In addition, Example 2, the content of the graphene oxide used in the total raw material mass of the electrode active material composite is 0.37 wt%, the charge capacity in the initial three cycles with a current density of 100 mA / g is 770 ~ 825 mAh / g In the severe current density condition of 500 mA / g, no decrease in capacity was observed from the fourth cycle, and the capacity was 561 mAh / g in the next 100 cycles, showing an excellent capacity retention of 83.3%.

In addition, Example 3, the content of the graphene oxide used in the total raw material mass of the electrode active material composite is 0.88 wt%, the charge capacity in the initial three cycles of the current density of 100 mA / g conditions is 890 ~ 930 mAh / g In the severe current condition of 500 mA / g, no decrease in capacity was observed from the fourth cycle, and the capacity was 633 mAh / g in 100 cycles afterwards, which was about 80.8% at the current density of 500 mA / g. Dose retention was shown.

On the other hand, the charge / discharge cycle characteristics of the secondary battery manufactured by using the silicon-carbon composite containing no graphene according to Comparative Example 1 as the electrode active material, the charge at the initial three cycles with a current density of 100 mA / g The capacity ranged from 800 to 815 mAh / g, and then gradually decreased from 672 mAh / g to 10 cycles to 582 mAh / g under severe current density of 500 mA / g. After the 10th cycle, the charge capacity remained in the range of 550-580 mAh / g, but after the 50th cycle, the capacity was reduced, and at 100 cycles the capacity was significantly reduced to about 200 mAh / g.

In addition, Table 2 below shows the capacity retention rate according to the characterization of the charge / discharge cycle of the composite prepared in Examples 1 to 3 and Comparative Example 1 as the electrode active material.

TABLE 2 Current density (mA / g) Cycle characteristics comparison item <unit> Example 1 Example 2 Example 3 Comparative Example 1 100 Discharge Capacity (3rd Cycle) <mAh / g> 700 826 930 825 500 Discharge capacity (5th cycle) <mAh / g> 548 675 766 648 500 5 to 50 cycle capacity retention <%> 81 90 89 84 500 50 to 100 cycle capacity retention <%> 95 93 93 36 500 5 to 100 cycle capacity retention <%> 77 83 83 30

As shown in Table 2, in the initial cycle, the capacity retention rate was found to be insignificant in Examples 1 to 3 and Comparative Example 1, but in the case of the silicon-graphene-carbon composite prepared in Examples 1 to 3 It can be seen that the 50-100 cycle capacity retention rate is 90% or more, and the average capacity retention rate of 5-100 cycles is 77% or more. On the other hand, in Comparative Example 1, which does not form a network between silicon-carbon particles, the capacity retention rate of 50 to 100 cycles is only 36%, and the average capacity retention rate of 5 to 100 cycles is only 30%. Could confirm.

FIG. 13 shows the results of analyzing the electrochemical characteristics of the secondary battery produced using the composite according to Example 2 as an electrode active material with respect to current densities different from those described above. At this time, the charge / discharge cycle characteristics were analyzed at the current density of 100 mA / g in the first three cycles and at the current density of 200 mA / g until the next 100 cycles, and the current density was 1000 mA / g from 100 cycles to 200 cycles. Cycle characteristics were analyzed at harsh conditions of g.

Referring to FIG. 13, the charging capacity in the initial three cycles under the current density of 100 mA / g was 730-740 mAh / g, and then decreased to 657 mAh / g in the fourth cycle under the current density of 200 mA / g. . Since then, at the 100th cycle under the same current density of 200 mA / g, the capacity was 674 mAh / g, showing very stable cycle characteristics without capacity reduction. Afterwards, under the high current density of 1000 mA / g, the initial capacity was 437 mAh / g, and after the 200th cycle, the capacity was maintained at 429 mAh / g, resulting in an excellent capacity of 98.2% during 100 cycles under 1000 mA / g. Retention rate is shown. In addition, the Coulombic efficiency was low about 54% in the first cycle, but greatly increased to 92.5% in the second cycle, and after the fifth cycle, the very high charge / discharge efficiency was maintained. Could.

In addition, Figure 14 shows the electrochemical characteristics of the secondary battery produced using the composite according to Example 4 and Example 5 as the electrode active material. The graphene oxide content in the total active material mass of the electrode active material composite is 0.1 wt%, and represents a silicon-graphene-carbon composite prepared using ammonium hydroxide as a catalyst for forming a composite gel.

In the composite according to Example 4, the charging capacity was 735 to 859 mAh / g at the initial 10 cycles at a current density of 100 mA / g, and then at the 11 th to 15th cycles at a harsh current density of 500 mA / g. The capacity was 601 mAh / g at 60 cycles after the reduction of the capacity, resulting in an excellent capacity retention of about 94.6% at 500 mA / g current density during the 15th to 60th cycles when the capacity was stable.

The composite according to Example 5 had a charge capacity of 1373 to 1586 mAh / g at an initial 10 cycle under a current density of 100 mA / g, and then 11 to 15 cycles under a severe current density of 500 mA / g. The capacity was reduced to 785 mAh / g at 60 cycles after the reduction of the capacity to about 90.1% at the current density of 500 mA / g during the 15th to 60th cycle where the capacity was stable.

Production Example 2 Lithium Secondary Battery (full cell) Manufacture

When the silicon nanoparticle-graphene-carbon composite having a graphene network formed therein prepared in Examples 1 to 5 is used as a real lithium secondary battery (full cell) anode, lithium secondary battery performance and electrochemical characteristics As an example to analyze the silicon nanoparticle-graphene-carbon composite having a graphene network formed therein according to Example 2 as a negative electrode, Ni-rich LNCM (Li [Ni _0.75 Co _0.1 Mn _0.15 ] O ₂ , 1C = 200 mA / g) to produce a full cell (lithium secondary battery full cell) using a positive electrode. Composite according to Example 2 was prepared by the method according to Preparation Example 1. The electrode prepared from the composite according to Example 2 was pretreated by a method of contacting with lithium metal in the electrolyte for about 1 hour to lower initial irreversibility, and then used to prepare a complete paper. Li-rich LNCM cathode active material, carbon black as a conductive material, PVDF (5 wt% solution dissolved in Polyvinylidene fluoride, N-methylpyrrolidinon (NMP)) as a polymer binder was prepared in order to manufacture a positive electrode at a weight ratio of 85: 7.5: 7.5. Mixing yielded a slurry mixture. The slurry was applied on an aluminum plate current collector, pressed, and then dried overnight at 120 ° C. in a vacuum.

In the glove box of the argon atmosphere, the composite cathode and the Ni-rich LNCM anode according to the pre-treated Example 2 were stacked in a coin cell at a capacity ratio of 1.2 (N / P ratio = 1.2), and the same separator used in Preparation Example 1, A lithium secondary battery full cell was prepared using an electrolyte solution.

Lithium secondary battery (full cell) Analysis of Electrochemical Properties of

For the electrochemical characterization of the prepared lithium secondary battery (full cell, full cell), the electrochemical characteristics and charge by a constant current method (1C = 200 mA / g) in the voltage range of 2.7 ~ 4.2V, room temperature (25 ℃) The discharge cycle characteristics were analyzed. The results are shown in FIG.

15A shows the charge / discharge voltage of a lithium secondary battery complete battery at a current density of 0.1 C relative to the positive electrode. The first charge and first discharge capacities were 206 and 196 mAh / g, respectively, indicating 95% charge / discharge efficiency.

15B shows charge / discharge cycle characteristics of the lithium secondary battery complete battery. The discharge capacity was 180 mAh / g in the second cycle under current density of 0.5C compared to the anode, and the discharge capacity was 170 mAh / g in the third cycle under current density of 1.0C. After the third cycle, the charge / discharge efficiency was higher than 98.5%. From the third cycle up to 750 cycles, the capacity retention was found to be very high at 88.4% under 1.0 C current density.

Therefore, the silicon-graphene-carbon composite in which a small amount of graphene is added to form a graphene network therein according to Examples 1 to 5 according to the present invention reacts with lithium, such as silicon, to produce a metal having a large volume change. When used as a lithium secondary battery negative electrode active material it can be seen that it is very effective to improve the cycle stability. In addition, the silicon-graphene-carbon composite having a graphene network formed therein was used as a cathode corresponding to a high-capacity cathode, and thus, it was confirmed that a lithium secondary battery complete battery having a very high energy density could be manufactured.

As a result of the analysis of the charge / discharge cycle characteristics, the graphene is dispersed in the interior prepared in Examples 1 to 5 according to the present invention to form a graphene network to form a graphene network as an electrode active material In this case, it showed excellent cycle stability. As the graphene having excellent conductivity, specific surface area, and mechanical elasticity is dispersed in the composite, it easily absorbs volume change even in repeated charge / discharge cycles and provides a conductive passage inside the electrode material. By forming and maintaining the conductive network, the stability of the charge / discharge cycle of the electrode is greatly improved, thereby greatly improving cycle life characteristics as the lithium secondary battery active material (see FIG. 3A). However, in the case of Example 1, Examples 4 and 5, the electrode active material of the silicon-graphene-carbon composite prepared from a raw material containing a small amount of graphene oxide of about 0.08 ~ 0.1 wt% has a low graphene content As in the case of Comparative Example 1, a capacity decrease was observed until the initial about seventh cycle under the current density of 500 mA / g (see FIGS. 12 and 14). On the other hand, in Examples 2 to 3, wherein the electrode active material is a silicon-graphene-carbon composite prepared from a raw material containing about 0.37 wt% to 0.88 wt% of graphene oxide, Comparative Examples 1 and 1 Unlike in the case of Examples 4 and 5, no large capacity reduction was observed until the initial about seventh cycle under the current density of 500 mA / g (see FIGS. 12 and 14).

On the other hand, when the silicon-carbon composite containing no graphene of Comparative Example 1 as an electrode active material, the initial capacity is high, but the charge / discharge cycle stability is low, there is a problem that the life of the electrode shortened after 50 cycles This is interpreted as a result of the loss of the conductive network due to the detachment of the electrode active material from the current collector or the cracking between the electrode active materials due to the large volume change caused by the repeated charge / discharge cycle characteristics of the silicon-based electrode active material (FIG. 3b). Reference).

According to the present invention, when a silicon-graphene-carbon composite having a graphene dispersed therein to form a graphene network is used as an electrode active material, it is industrially used as an electrode material for secondary batteries having high capacity and significantly extending cycle life. There is a high possibility, and especially according to the production method of the present invention, it is expected that mass production can be easily performed by the sol-gel method.

Claims (15)

Metal nanoparticles reacting with lithium; Carbon coated on the outside of the nanoparticles; And Graphene to form a uniform network between the nanoparticles; including, nanoparticle-graphene-carbon composite formed with a graphene network therein. The method of claim 1, The metal nanoparticles, characterized in that it comprises 20 to 80% by weight of the total weight of the composite, nanoparticle-graphene-carbon composite with a graphene network formed therein. The method of claim 1, The metal nanoparticles, Si, Sn, As, Ge, Bi, Al, In, Pb and Ga, characterized in that the graphene network therein, characterized in that the mixture of one or more metal nanoparticles or one or more metal nanoparticles. Formed nanoparticle-graphene-carbon composite. The method of claim 1, The nanoparticles are characterized in that the average particle diameter of 1 ~ 200 nm size, nanoparticle-graphene-carbon composite formed with a graphene network therein. Forming a composite gel by adding a carbon precursor and a catalyst to an aqueous solution containing metal nanoparticles reacting with lithium and graphene oxide; And Heat-treating the composite gel; and a method for producing a nanoparticle-graphene-carbon composite comprising: The nanoparticle-graphene-carbon composite is characterized in that the composite according to any one of claims 1 to 4, wherein the graphene network formed nanoparticle-graphene-carbon composite method. The method of claim 5, The metal nanoparticles, Si, Sn, As, Ge, Bi, Al, In, Pb and Ga, characterized in that the graphene network therein, characterized in that the mixture of one or more metal nanoparticles or one or more metal nanoparticles. Method for producing a nanoparticle-graphene-carbon composite is formed. The method of claim 5, The graphene oxide is characterized in that it comprises 0.05 to 2.0% by weight relative to the weight of the total raw material to form a composite gel, a graphene network formed nanoparticle-graphene-carbon composite therein. The method of claim 5, The carbon precursor is a nanoparticle-graphene-carbon composite having a graphene network formed therein, characterized in that one or more mixtures selected from resorcinol-formaldehyde, phenol-formaldehyde or perperyl alcohol. Manufacturing method. The method of claim 5, The catalyst is sodium carbonate, sodium hydrogen carbonate, sodium hydroxide, ammonium chloride or ammonium hydroxide, characterized in that the production of nanoparticle-graphene-carbon composites with a graphene network formed therein, characterized in that one or more Way. The method of claim 5, The composite gel formation is characterized in that at a temperature of 60 ~ 90 ℃ in a closed reactor, the graphene network formed nanoparticle-graphene-carbon composite method therein. The method of claim 5, The heat treatment is characterized in that the inert gas or a mixed gas atmosphere of inert gas and hydrogen is carried out at a temperature range of 600 ~ 1000 ℃, graphene network formed nanoparticle-graphene-carbon composite therein. The secondary battery electrode, characterized in that it comprises a current collector coated with the nanoparticle-graphene-carbon composite according to any one of claims 1 to 4. The method of claim 11, The current collector is characterized in that the nanoparticle-graphene-carbon composite is coated with PVA (Poly vinyl acetate) or PAA (Poly acrylic acid) or CMC (Carboxymethyl Cellulose) as a polymer binder, the secondary battery electrode. A secondary battery comprising the secondary battery electrode and the electrolyte according to claim 11. Power storage device and electronic device comprising a secondary battery according to claim 11 as a power supply source.

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