KR102690258B1 - Manufacturing method for silicon negative electrode material having a structure of yolk-shell - Google Patents

Abstract

The present invention includes the steps of a) forming a first polymer coating layer containing polymethylmethacrylate on the surface of Si particles; b) forming a second polymer coating layer containing melanin polymer on the first polymer coating layer; and c) removing the first polymer coating layer through heat treatment to form voids and carbonizing the second polymer coating layer to convert it into a carbon layer. A Si cathode with a yolk-shell structure comprising a. It is about a method of manufacturing ash.

Description

Method for manufacturing Si anode material with yolk-shell structure {MANUFACTURING METHOD FOR SILICON NEGATIVE ELECTRODE MATERIAL HAVING A STRUCTURE OF YOLK-SHELL}

The present invention relates to a method of manufacturing a Si anode material with a yolk-shell structure.

Recently, interest in energy storage technology has been increasing. As application areas expand to include mobile phones, camcorders, laptop PCs, and even electric vehicles, efforts to research and develop electrochemical devices are becoming more concrete.

Electrochemical devices are the field that is receiving the most attention in this regard, and among them, the development of secondary batteries capable of charging and discharging has become the focus of attention. Recently, in the development of such batteries, efforts have been made to improve capacity density and energy efficiency. Research and development is underway on the design of new electrodes and batteries.

Among the secondary batteries currently in use, the lithium secondary battery developed in the early 1990s has the advantage of having a higher operating voltage and much higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and lead sulfate batteries that use aqueous electrolyte solutions. is in the spotlight.

Among these, graphite, which is used as a negative electrode material for existing lithium-ion batteries, has reached its limit in capacity (372 mAh/g at 25 ℃), and accordingly, silicon (3580 mAh/g at 25 ℃), which has a higher theoretical capacity than graphite, is being used as an anode material. It is time for development.

This silicon has a capacity of 3600 mAh/g, 10 times that of graphite. However, these silicon (Si) anode materials have not yet been commercialized despite their high capacity. This is because volume expansion and contraction of close to 300% are repeated during charging and discharging, and the SEI layer formed on the surface of the Si cathode material is also created/destructed. This is because battery life deteriorates rapidly as it is repeated.

A Si cathode material with a Yolk-Shell structure has been proposed as a Si cathode material that can accommodate this change in Si volume and prevent repeated creation/destruction of the SEI layer.

As a conventional technology for manufacturing Si anode materials with a yoke-shell structure, a method involves coating the surface of Si particles with silica, coating the surface of the silica with a carbon layer, and then etching the silica with hydrofluoric acid to form a Si@void@C structure. It is known. This method is not only dangerous because it uses hydrofluoric acid, but also has the problem of increasing the manufacturing process cost.

Nano Today (2012) 7, 414―429

In the case of the prior art, a carbon layer was coated on the surface of silica and then the silica was etched with hydrofluoric acid to form a Si@void@C structure, which was not only dangerous but also increased the manufacturing process cost.

Accordingly, after conducting various studies, the present inventors discovered that by forming voids by coating the polymer on the surface of Si and removing it through heat treatment, a yoke-shell (Yolk-shell) with increased initial efficiency and excellent rate characteristics can be obtained in a simple method. It was confirmed that a silicon anode material with a shell structure could be developed.

Therefore, the purpose of the present invention is to provide a method for manufacturing a Si anode material with a yoke-shell structure that increases initial efficiency and has excellent rate characteristics and cycle stability.

In order to achieve the above object, the present invention includes the steps of a) forming a first polymer coating layer containing polymethylmethacrylate on the surface of Si particles; b) forming a second polymer coating layer containing melanin polymer on the first polymer coating layer; and c) removing the first polymer coating layer through heat treatment to form voids and carbonizing the second polymer coating layer to convert it into a carbon layer. A Si cathode with a yolk-shell structure comprising a. Provides a method for producing ash.

Additionally, the present invention provides a Si anode material with a yolk-shell structure manufactured by the above method.

Additionally, the present invention provides a negative electrode for a lithium secondary battery including the negative electrode material.

In addition, the present invention provides the cathode; anode; separation membrane; It provides a lithium secondary battery including; and an electrolyte.

According to the present invention, a Si anode material with a yolk-shell structure can be synthesized to have a volume expansion buffer structure. Accordingly, when applied to a battery, it has the effect of reducing electrolyte penetration, thereby increasing initial efficiency, and has the advantage of excellent rate characteristics and cycle stability.

In addition, according to the present invention, there is an advantage that a Si anode material can be manufactured using a heat treatment method that is more stable and inexpensive than the conventional method.

Figure 1 is a schematic diagram showing the manufacturing process of a Si anode material with a yolk-shell structure according to an embodiment of the present invention.
Figure 2 is an SEM photograph of Si micro particles used in the present invention.
Figure 3 is an IR spectrum graph before and after grafting in Example 1 of the present invention.
Figure 4 is a photograph showing hydrophobicity before and after grafting in Example 1 of the present invention.
Figure 5 is a graph showing the change in PMMA content according to temperature change in an example of the present invention.
Figure 6 is a graph showing the change in PMMA content according to the change in the amount of MMA introduced in the embodiment of the present invention.
Figures 7 to 11 are SEM photographs of Si@PMMA prepared in examples of the present invention.
Figure 12 is a schematic diagram showing step-by-step coating, carbonization, and CVD processes according to an embodiment of the present invention.
Figures 13 to 15 are graphs showing differences in thermogravimetric analysis values according to step-by-step coating, carbonization, and CVD processes according to embodiments of the present invention.
Figures 16 to 18 are graphs showing differences in nitrogen adsorption test results according to step-by-step coating, carbonization, and CVD processes according to embodiments of the present invention.
Figures 19 to 21 are graphs showing the pore distribution of mesopores according to step-by-step coating, carbonization, and CVD processes according to an embodiment of the present invention.
Figures 22 and 23 are graphs measuring XRD of Si@V25@C and Si@V25@G during the CVD process according to an embodiment of the present invention.
Figures 24 and 25 are graphs measuring Raman spectra of Si@V25@C and Si@V25@G during the CVD process according to an embodiment of the present invention.
Figures 26 and 27 are graphs measuring XRD of Si@V45@C and Si@V45@G during the CVD process according to an embodiment of the present invention.
Figures 28 and 29 are graphs measuring Raman spectra of Si@V45@C and Si@V45@G during the CVD process according to an embodiment of the present invention.
Figures 30 to 32 are SEM photographs measuring Si@V45@G according to an embodiment of the present invention.
Figure 33 is a TEM photograph measuring Si@V45@G according to an embodiment of the present invention.
Figures 34 to 36 are graphs showing capacity characteristics according to an embodiment of the present invention.
Figure 37 is a graph showing rate characteristics according to an embodiment of the present invention.
Figures 38 and 39 are graphs showing the results of the capacity characteristics of silicon micro particles to confirm the capacity according to the voltage cut-off.
Figures 40 and 41 are graphs showing the results of voltage cut-off experiments when curing was performed in an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to this specification.

In the drawings, parts unrelated to the description are omitted in order to clearly explain the present invention, and similar reference numerals are used for similar parts throughout the specification. Additionally, the sizes and relative sizes of components shown in the drawings are unrelated to actual scale and may be reduced or exaggerated for clarity of explanation.

How to manufacture Si anode material

The method of manufacturing a Si anode material with a yolk-shell structure of the present invention includes the steps of a) forming a first polymer coating layer containing polymethylmethacrylate on the surface of Si particles; b) forming a second polymer coating layer containing melanin polymer on the first polymer coating layer; and c) removing the first polymer coating layer through heat treatment to form voids and carbonizing the second polymer coating layer to convert it into a carbon layer.

In the present invention, the structure of yoke-shell particles is a term derived from egg and refers to a structure with an empty space between the core and shell, just as an egg has a structure of yolk, white, and shell. To this end, at least a portion of the shell of the yoke-shell structured particle of the present invention is spaced apart from the core.

In the present invention, a Si anode material with a yolk-shell structure can be manufactured through the process shown in FIG. 1. Below, we will look at it in detail.

First, the method of manufacturing a Si anode material with a yolk-shell structure of the present invention includes the steps of a) forming a first polymer coating layer containing polymethylmethacrylate on the surface of the Si particle. Includes.

There is no particular limitation on the Si (silicon) used in step (a), but preferably one commonly used in the industry can be used, preferably with an average particle diameter of 500 nm to 10 μm, more preferably 1 μm to 5 μm. Silicone having can be used. If the size of the silicon particles is less than 500 nm, as the specific surface area increases, the first cycle coulombic efficiency may decrease.

In step (a), the surface of the silicon particle is reacted with methylmetacrylate (MMA), a polymer precursor, to effectively form a first polymer coating layer containing polymethylmethacrylate through a chemical reaction with the acrylic group on the silicon surface. .

Here, before forming the first polymer coating layer, the surface of the Si particle is modified (grafting) with 3-(Trimethoxysilyl)propyl methacrylate (MPS) and then reacted with methylmetacrylate (MMA), -O on the silicon surface. Alternatively, as the -OH group is replaced with an acryl group, the first polymer coating layer containing polymethylmethacrylate can be formed more easily.

When reacting the methylmetacrylate (MMA) with the silicon surface, the reaction can be preferably performed at a temperature of 62 to 70°C, and more preferably at a temperature of 63 to 68°C. When the reaction proceeds in the above temperature range, the amount of PMMA formed on the silicon particles can be formed faster and in greater amounts.

Afterwards, the method of manufacturing a Si anode material with a yolk-shell structure of the present invention includes the step of b) forming a second polymer coating layer containing melanin polymer on the first polymer coating layer. Includes.

In step b), after measuring the charge on the surface of the first polymer coating layer, the surface charge can be adjusted using a CTAB solution to induce a surface-selective polymer reaction to occur.

Afterwards, the method of manufacturing a Si anode material with a yolk-shell structure of the present invention is c) removing the first polymer coating layer through heat treatment to form a void, and the second polymer coating layer is It includes the step of carbonizing and converting into a carbon layer.

Through the heat treatment, the first polymer coating layer containing PMMA, a thermal decomposition polymer, is removed by thermal decomposition to form voids in the yoke-shell structure, and the second polymer coating layer containing melanin polymer is carbonized. It is converted to carbon to form a shell with a yoke-shell structure.

The heat treatment in step c) may be performed in an N ₂ atmosphere at a temperature of 500 to 700°C for 2 to 5 hours. When the above heat treatment conditions are met, there is an advantage in maintaining the yoke-shell structure without reducing voids in the subsequent CVD reaction.

Afterwards, the method of manufacturing a Si anode material with a yolk-shell structure of the present invention is d) using a carbon precursor to block the pores of the carbonized carbon layer using CVD, and then graphitizing it through heat treatment. Steps may be further included. In step d), CH ₃ CN can be deposited on Si@Void@MC (Melanin polymer derived carbon) by CVD, and then heat treatment is performed to block the micropores of the mesoporous carbon, and graphitic carbon is synthesized according to the present invention. It is possible to manufacture Si anode materials with a yolk-shell structure. At this time, the CVD can deposit CH ₃ CN by bubbling Acetonitrile at a temperature increase rate of 20 to 40°C/min and 900 to 1,100°C in an N ₂ atmosphere and maintaining it for 0.5 to 2 hours. When the above CVD conditions are met, the structure of Si@Void@MC is maintained and there is an advantage in that the carbon layer can be converted to a graphite layer.

Additionally, before proceeding with the CVD, curing may be performed at a temperature of 150 to 250° C. for 2 to 5 hours. If curing is performed as above, there is an advantage in reducing the shrinkage process of the polymer and converting to a stable yoke-shell structure without damage to the structure.

When manufactured as described above, the Si anode material of the yoke-shell structure of the present invention may have a specific surface area of 50 m ² /g or less, preferably 5 to 30 m ² /g. As the specific surface area increases, the contact area with the electrolyte increases, so the possibility of a side reaction with the electrolyte increases, which reduces initial efficiency.

Anode for lithium secondary battery

The particles of the yoke-shell structure presented in the present invention can be preferably used as a negative electrode material for a negative electrode for lithium secondary batteries.

The negative electrode includes a negative electrode active material formed on a negative electrode current collector, and the negative electrode active material uses particles with a yoke-shell structure manufactured according to the present invention.

The negative electrode current collector may be specifically selected from the group consisting of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, non-conductive polymer surface-treated with a conductive material, or conductive polymer may be used.

The negative electrode may further include binder resin, conductive material, filler, and other additives.

The binder resin is used to bond the electrode active material and the conductive material and to the current collector. Non-limiting examples of these binder resins include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), and polymethyl methacrylate (PMMA). Amide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), alginic acid, alginate, chitosan, carboxymethyl cellulose ( CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR) ), fluorine rubber, and various copolymers thereof.

The conductive material is used to further improve the conductivity of the electrode active material.　These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and examples include graphite such as natural graphite or artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives, etc. may be used.

Lithium secondary battery

As an embodiment of the present invention, a lithium secondary battery includes the above-described negative electrode; anode; and electrolyte;

The lithium secondary battery according to the present invention includes a positive electrode and a negative electrode, a separator and an electrolyte interposed between them, and uses particles with a yoke-shell structure manufactured according to the present invention as a negative electrode active material.

The yoke-shell structured particles manufactured according to the present invention can alleviate capacity degradation caused by volume expansion of silicon and exhibit excellent electrical conductivity and capacity retention rate.

The configuration of the positive electrode, negative electrode, separator, and electrolyte of the lithium secondary battery is not particularly limited in the present invention and follows what is known in the field.

The positive electrode is used including a positive electrode active material formed on the positive electrode current collector. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, Titanium, fired carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. can be used. At this time, the positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics with fine irregularities formed on the surface to increase adhesion with the positive electrode active material.

The cathode active material constituting the electrode layer can be any cathode active material available in the art. Specific examples of such positive electrode active materials include lithium cobalt-based oxides such as LiCoO ₂ ; Lithium manganese-based oxides such as Li _{1 + x} Mn _{2 - x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; Lithium copper oxide such as Li ₂ CuO ₂ ; Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; LiNi _{1 -} lithium nickel-based oxide expressed as _x M _x O ₂ (where M=Co, Mn, Al, Cu, Fe, Mg, B or Ga and x=0.01 to 0.3); LiMn _{2 - x} MxO ₂ (where M=Co, Ni, Fe, Cr, Zn or Ta, and x=0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M=Fe, Co, Ni, Cu) or Zn); lithium manganese composite oxide expressed as Li(Ni _a Co _b Mn _c )O ₂ (here, 0<a<1, 0<b＜1, 0＜c＜1, a+b+c=1) Lithium-nickel-manganese- cobalt-based oxide; Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Sulfur or disulfide compounds; Phosphates such as LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , and LiNiPO ₄ ; Fe ₂ (MoO ₄ ) ₃ etc. may be mentioned, but it is not limited to these alone.

At this time, the electrode layer may further include binder resin, conductive material, filler, and other additives in addition to the positive electrode active material.

The binder resin is used to bond the electrode active material and the conductive material and to the current collector. Non-limiting examples of these binder resins include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), and polymethyl methacrylate (PMMA). Amide (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), alginic acid, alginate, chitosan, carboxymethyl cellulose ( CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR) ), fluorine rubber, and various copolymers thereof.

The conductive material is used to further improve the conductivity of the electrode active material.　These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and examples include graphite such as natural graphite or artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives, etc. may be used.

As the cathode, the cathode of the present invention described above can be used.

The separator may be made of a porous substrate. Any porous substrate commonly used in electrochemical devices can be used. For example, a polyolefin-based porous membrane or non-woven fabric can be used, but this is not particularly limited. no.

The separator is made of polyethylene, polypropylene, polybutylene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, It may be a porous substrate made of any one selected from the group consisting of polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, or a mixture of two or more of these.

The electrolyte solution of the lithium secondary battery is a non-aqueous electrolyte containing a lithium salt and is composed of a lithium salt and a solvent. The solvent used includes a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte.

The lithium salt is a material that is easily soluble in the non-aqueous electrolyte solution, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiSCN, LiC ₄ BO ₈ , LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiC(CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ )·2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate imide, etc. can be used.

Non-aqueous organic solvents include, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2 -Dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, Diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3- Aprotic organic solvents such as dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

The organic solid electrolyte includes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, Polymers containing secondary dissociation groups, etc. may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitride, halide, sulfate, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ may be used.

Additionally, the non-aqueous electrolyte may further contain other additives for the purpose of improving charge/discharge characteristics, flame retardancy, etc. Examples of the additives include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolyl. Dinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), vinylene carbonate ( VC), etc.

The lithium secondary battery according to the present invention is capable of lamination (stack) and folding processes of separators and electrodes in addition to the general winding process. Additionally, the battery case may be cylindrical, prismatic, pouch-shaped, or coin-shaped.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the attached patent claims.

[Example]

Manufacturing of silicon-carbon anode material

[Example 1]

Step 1: Si@PMMA fabrication (coating the first polymer layer on the Si surface)

As shown in Figure 2, after preparing Si with an average particle size of 10 μm, the surface of the Si particles was subjected to a hydrolysis reaction using an alkoxide to replace it with an acrylate group. In order to induce an effective surface reaction by substituting the relatively hydrophilic surface of Si with an acrylate functional group, which is a unit of PMMA, 100 mg of Si and 0.1 mL of 3-(trimethoxysilyl)propyl methacrylate (MPS) per 100 mL of EtOH were placed in a plastic bottle. After closing the lid, the mixture was stirred at 90°C for 24 hours. Figure 3 shows the IR spectrum before and after the reaction, through which the C=C and =C-H functional groups could be confirmed.

In addition, in order to confirm the hydrophobicity of Si before and after the reaction, Si was immersed in water and MMA, as shown in Figure 4, and through this, it was confirmed that the hydrophobicity was improved by grafting.

Step 2: Si@PMMA@MP (melanin polymer) preparation ( Si on the surface 2nd polymer layer coating)

1) Si@PMMA synthesis using seeded growth reaction

After preparing 50 mL of a 1:1 mixed solution of DI water and EtOH in a 100 mL round bottomed flask, 0.5 mg of Initiator (2,2'-azobis(2-methylpropionamidine) dihydrochloride) and 100 mg of PVP (Poly Vinyl Pyrrolydone) were added. mg was dissolved in order. Afterwards, the flask was placed in a 60°C silicon oil bath and N ₂ bubbling was performed for 1.5 hours. Afterwards, 30 mg of Si was dispersed in 1 mL of MMA, and the solution in which MMA and Si were dispersed was added using a syringe to start the reaction. Afterwards, 1 mL of MMA was added every 15 minutes, and after 3 hours, it was washed with DI water and dried. The Si@PMMA prepared in this way was photographed with SEM equipment, HITACHI's S-4800, and shown in Figures 7 to 11.

2) Si@PMMA@MP (melanin polymer) / Si@void@MC synthesis through surface modification

Afterwards, 50 mg of Si@PMMA prepared above was dispersed in 38 mL of DI water. Afterwards, 0.5 mL of 2 mM CTAB (Cetyl Trimethyl Ammonium Bromide) and 0.02 mL of NH ₃ were added to the solution, and then 94 mg of Melanin was added to proceed with the reaction. Afterwards, after washing with DI water and drying, carbonization was carried out at 600°C for 3 hours at a temperature increase rate of 5°C/min in N ₂ atmosphere.

3) Si@void@G_no curing

Afterwards, the temperature was maintained at 200°C for 3 hours and then carbonization was carried out at 600°C for 3 hours at a temperature increase rate of 5°C/min.

4) CVD (Chemical Vapor Deposition) reaction progresses

A CVD (Chemical Vapor Deposition) reaction was performed to introduce additional graphitic carbon to the surface of the material. Specifically, in an N ₂ atmosphere, acetonitrile bubbling (Flow rate: 500 cc/h) was maintained for 1 hour at a temperature increase rate of 30 ℃/min and 1000 ℃, and Si@PMMA / Si@void@G was synthesized to produce anode material. did.

[Example 2]

In step 2, “1) Si@PMMA synthesis using seeded growth reaction,” the same method as Example 1 except that MMA was added in 0.5 mL increments instead of 1 mL in 15-minute increments. An anode material was manufactured.

[Comparative Example 1]

Step 1: Si@PMMA fabrication (coating the first polymer layer on the Si surface)

It was prepared in the same manner as Example 1.

Step 2: Si@PMMA@MP (melanin polymer) preparation ( Si on the surface 2nd polymer layer coating)

1) Si@PMMA synthesis using seeded growth reaction

It was prepared in the same manner as in Example 1, except that the temperature of the silicon oil bath was set to 65°C, the PVP content was 100 mg, and additional MMA was introduced every 30 minutes.

2) Si@PMMA@MP (melanin polymer) / Si@void@MC synthesis through surface modification

An anode material was prepared by synthesizing Si@void@MC in the same manner as in Example 1, except that 112 mg of melanin was used.

Experimental Example 1: Evaluation of Si@void@C anode material properties

1) Change in PMMA content depending on temperature

In step 2 of the manufacturing process of Example 1 and Comparative Example 1, “1) Si@PMMA synthesis using seeded growth reaction,” the synthesis was performed with the temperature of the silicon oil bath set to 65°C. The change in PMMA content of Si@void@C prepared in Example 1 and Comparative Example 1, which was synthesized at 60°C, and Si@void@C prepared in Comparative Example 1 was measured using thermogravimetry analysis (Thermo Gravimetry Analysis, It was measured using TGA) and is shown in Table 1 and Figure 5 below.

Solvent (mL) EtOH: HO Si (mg) Temp. (oC) Time (h) PVP
(mg) MMA (mL) Initiator
(mg [wt%]) TGA
(wt% of PMMA) line
city
yes
One 100 5:5 30 65 10min 100 One [0.15] 13.7 100 5:5 30 65 20min 100 One [0.15] 17 100 5:5 30 65 30min 100 One [0.15] 23.4 100 5:5 30 65 60min 100 One [0.15] 26

Through Table 1 and Figure 5, it was found that the PMMA content in Example 1, where synthesis was performed at 65°C, increased more rapidly.

2) Change in PMMA content depending on the amount of MMA

In the process of "1) Si@PMMA synthesis using seeded growth reaction" in step 2 of the manufacturing process of Example 2 and Comparative Example 1, 1 mL of MMA was added in Example 1 and 0.5 mL of MMA was added in Example 2. The change in PMMA content of the prepared Si@void@C was measured using Thermo Gravimetry Analysis (TGA), and is shown in Table 2 and Figure 6 below.

Solvent (mL) EtOH: HO Si (mg) Temp. (oC) Time (h) PVP
(mg) MMA (mL) Initiator
(mg [wt%]) TGA
(wt% of PMMA) line
city
yes
One 100 5:5 30 65 10min 100 One [0.15] 13.7 100 5:5 30 65 20min 100 One [0.15] 17 100 5:5 30 65 30min 100 One [0.15] 23.4 100 5:5 30 65 60min 100 One [0.15] 26 line
city
yes
2 100 5:5 30 65 10min 100 0.5 [0.15] 18 100 5:5 30 65 20min 100 0.5 [0.15] 30 100 5:5 30 65 30min 100 0.5 [0.15] 33 100 5:5 30 65 60min 100 0.5 [0.15] 35

Through Table 2 and Figure 6, it was found that the PMMA content in Example 2, where the synthesis was performed by administering 0.5 mL each, increased more rapidly.

3) Seeded growth changes

Based on the results confirmed in Example 1 in Table 1 and Examples 1 and 2 in Table 2, the injection time of additional MMA was fixed at 30 minutes, and Examples 1 and 0.5 mL each of MMA were added. The change in PMMA content of Si@PMMA prepared in 2 was measured using Thermo Gravimetry Analysis (TGA) and is shown in Table 3.

Solvent (mL) EtOH: HO Si (mg) Temp. (oC) Time (h) PVP
(mg) MMA (mL) number Initiator
(mg [wt%]) TGA
(wt% of PMMA) 100 5:5 30 65 3 100 One 0.5*1 [0.15] 38 100 5:5 30 65 3 100 One 0.5*2 [0.15] 42 100 5:5 30 65 3 100 One 0.5*3 [0.15] 38 100 5:5 30 65 3 100 0.5 0.5*1 [0.15] 45 100 5:5 30 65 3 100 0.5 0.5*2 [0.15] 42 100 5:5 30 65 3 100 0.5 0.5*3 [0.15] -

4) Synthesis step by step thermogravity Analytical value measurement

As shown in Figure 12, the differences in thermogravimetric analysis values according to each stage of coating, carbonization, and CVD according to the examples of the present application are shown in Figures 13 to 15.

Specifically, Figures 13, 14, and 15 show the weight percentages of carbon synthesized through thermal reaction and carbon additionally synthesized through CVD through Tg measurements before and after CVD reaction.

5) Nitrogen isothermal adsorption experiment at each stage of synthesis

Likewise, the differences in nitrogen adsorption results according to step-by-step coating, carbonization, and CVD according to the examples of the present application are shown in Figures 16 to 18.

Specifically, Figure 16 shows the comparison of the nitrogen isothermal adsorption curves of Si@V0@C and Si@V0@G, and Figure 17 shows the nitrogen isothermal adsorption curves of Si@V25@C and Si@V25@G. The compared values are shown, and Figure 18 shows the compared nitrogen isothermal adsorption curves of Si@V45@C and Si@V45@G.

6) Pore distribution at each stage of synthesis ( dV / dlogd ) check

Likewise, the differences in mesopore distribution according to each step of coating, carbonization, and CVD according to the examples of the present application are shown in Figures 19 to 21.

Specifically, Figure 19 shows a comparison of the mesopore distributions of Si@V0@C and Si@V0@G, and Figure 20 shows a comparison of the mesopore distributions of Si@V25@C and Si@V25@G. The values are shown, and Figure 21 shows the values comparing the mesopore distribution of Si@V45@C and Si@V45@G.

In addition, the specific surface area (S _BET ) and total volume (V _tot ), pore volume (V _micro ), and TG values were tested for nitrogen adsorption using BEL mini nitrogen adsorption equipment from BEL, and the results were measured and shown in Table 4 below.

Target S _BET ( ^m2 /g) V _tot ( ^cm3 /g) V _micro (cm ³ /g) TG (wt%) Si@V0@C 184 0.13 0.071 44.6 Si@V0@G 14 0.01 0.01 36 Si@V25@C 211 0.16 0.067 50.7 Si@V25@G 11 0.10 - 37.4 Si@V45@C 335.7 0.74 0.063 53.8 Si@V45@G 4 0.006 - 39.1

Through Table 4 above, it can be seen that pore block can be performed through this method as the surface area and micropore volume of the composite decrease before and after the CVD reaction.

7) Sample carbon graphitization Check the degree

Likewise, the degree of graphitization of carbon samples of Si@V25@C, Si@V25@G, Si@V45@C, and Si@V45@G according to step-by-step coating, carbonization, and CVD according to the embodiments of the present application is shown in Figures 22 to 22. Shown in 29.

Through Figures 22 to 29, it was seen that graphitic properties were improved by carbon after CVD reaction.

Additionally, Si@V45@G was photographed with S-4800 from HITACHI, a SEM equipment, and shown in Figures 30 to 32, and photographed with JEM-2100F from JEOL, a TEM equipment, and shown in Figure 33.

Experiment example 2: Half-cell production and charging/discharging conditions testing

The anode material made of Si@V0@C, Si@V0@G, Si@V25@C, Si@V25@G, Si@V45@C and Si@V45@G of Example 1 and Comparative Example 1 was used as a cathode. A battery was manufactured using the active material.

First, the negative electrode active material prepared in Example 1 and Comparative Example 1: binder (Polyamide imide (PAI)): conductive material (Super-P) were mixed in a weight ratio of 6: 2: 2, and NMP was used as a solvent. A slurry was prepared using.

The prepared slurry was applied to Cu foil to a thickness of 40 μm using a doctor blade, and a cathode was manufactured by heat treatment at 350°C for 1.5 hours in an Ar atmosphere to increase the binder effect of PAI.

Afterwards, a coin 2032 type cell was used for the half cell, the electrolyte was mixed at EC: DEC = 30:70 vol%, 10 wt% of FEC was used as an additive, and 1.3M LiPF ₆ was used as a lithium salt to form a half cell. was manufactured.

To create a stable SEI layer, the capacitance characteristics experiment was conducted under the conditions of 0.01-1.5V 0.1C in the first cycle, 0.01-1.0V 0.1C in the second cycle, and 0.01-1.0V 0.5C from the third cycle. proceeded with. At this time, a 0.02C cut off current was used in all cycles.

The rate characteristic experiments were all the same as the cycle characteristics, and were conducted under 0.2C, 0.5C, 1C, 2C, and 5C conditions for 5 cycles each in the 3rd cycle.

In the case of the voltage cut-off experiment, the method was the same as the capacity characteristics experiment, but the 0.02C cut-off current was not introduced in all cycles, and the experiment was conducted by setting the lowest voltage to 0.01, 0.05, 0.1, and 0.15 V depending on the conditions. .

1) Capacity characteristics

The anode material made of Si@V0@C, Si@V0@G, Si@V25@C, Si@V25@G, Si@V45@C and Si@V45@G of Example 1 and Comparative Example 1 was used as a cathode. After manufacturing the battery using the active material, the capacity characteristics of each battery were compared and shown in Figures 34 to 36, and the rate characteristics according to the progress of each cycle are shown in Figure 37.

Through Figures 34 to 37, it can be seen that the capacity retention rate improves as the free space due to PMMA increases, and the capacity and capacity retention rate of the material improve along with the initial efficiency after the CVD reaction progresses.

In addition, the cathode made of Si@V0@C, Si@V0@G, Si@V25@C, Si@V25@G, Si@V45@C, and Si@V45@G of Example 1 and Comparative Example 1 The properties of the ash were compared and shown in Table 5.

TG(Si wt%) S _BET ( ^m2 /g) 1 ^st Cycle CE ^1st Charge ^1st Discharge Capacity maintenance rate @50 cycle Capacity @50cycle(mAh/g) Si - - 74.2 3792 2813 8% 231 Si@V0@C 54.6 184 69.9 2092 1463 24% 361 Si@V0@G 41.2 14 71.9 2062 1483 49% 731 Si@V25@C 50.7 211 75.2 2107 1584 - - Si@V25@G 37.4 11 80.2 2421 1944 - - Si@V45@C 42.3 335.7 77.3 1733 1341 65.2% 1067.1 Si@V45@G 33.9 4 84.9 1709 1451 93.8% 1352.4

Through Table 5 above, it can be seen that the capacity retention rate improves as the free space by PMMA increases, and the capacity and capacity retention rate of the material improve along with the initial efficiency after the CVD reaction progresses.

2) Voltage cut-off experiment

A voltage cut-off experiment was conducted, and the results are shown in Table 6 and Figures 38 to 39 below.

Voltage cut-off Capacity(mah/g) Volume expansion Ideal 4200 400 0.005 3854 363 0.05 2443 232 0.1 1470 140 0.15 1200 113

Through Table 6 and Figures 38 and 39, the capacity at a specific voltage was confirmed through the charging and discharging results for the actual silicon nanoparticles, and the volume expansion rate was calculated by comparing the capacity at this time with the theoretical capacity.

3) In curing Capacity characteristics according to

In Example 1 and Comparative Example 1, a battery was manufactured using Si@V45@G15 and Si@V45@G23 anode materials prepared through a curing process as an anode active material, and then the capacity characteristics of Si@V45@G15 were measured. It is shown in Figure 40, and the capacity characteristics of Si@V45@G23 are shown in Figure 41.

Through Figures 40 and 41, it was seen that the capacity characteristics of the material were improved after curing.

4) Measurement of thickness change rate

In Example 1 and Comparative Example 1, Si@V0@C, Si@V0@G, Si@V25@C, Si@V25@G, Si@V45@C, Si@V45@G prepared without curing process. and Si@V45@G15, the thickness of the electrode upon discharge after 50 cycles is shown in Table 7 by measuring the thickness of the electrode before the cycle.

Thickness change rate ^{1 )} Si@V25@C 12.4 →17.7 (42.7%) Si@V25@G 12.4 →17.5 (41.1%) Si@V45@C 13.6 →16.3 (19.8%) Si@V45@G15 (0.05V) ²⁾ 12.9 →15.7 (21.7%) Si@V45@G15 (0.1V) 12.9 →15.5 (20.1%) Si@V45@G15 (0.15V) 12.9 →16.3 (26.3%) Si@V45@G20 (0.005V) 13.1 →15.8 (20.6%) Si@V45@G20 (0.1V) 13.3 →16.3 (22.5%) Si@V45@G20 (0.15V) 13.3 →16.3 (22.5%)

(1: Unit is um. @50 (discharge) vs 51 (charge) cycle basis

2: Lowest voltage set when charging and discharging)

Through Table 7 above, it can be seen that the thickness change rate decreases as the free space due to PMMA increases, and when the free space is sufficient, a similar thickness change rate can be confirmed regardless of the voltage cut-off.

Claims (12)

a) forming a first polymer coating layer containing polymethylmethacrylate on the surface of the Si particle;
b) forming a second polymer coating layer containing melanin polymer on the first polymer coating layer; and
c) removing the first polymer coating layer through heat treatment to form voids and carbonizing the second polymer coating layer to convert it into a carbon layer; Si anode material with a yolk-shell structure comprising a How to manufacture. According to paragraph 1,
d) blocking the pores of the carbon layer by using a carbon precursor using CVD and then graphitizing it through heat treatment. According to paragraph 1,
Before forming the first polymer coating layer, the surface of the Si particle is modified (grafting) with 3-(Trimethoxysilyl)propyl methacrylate (MPS) and then reacted with methylmetacrylate (MMA) to form the first polymer layer. -Method of manufacturing Si anode material with yolk-shell structure. According to paragraph 1,
In step a), MMA (methylmetacrylate) is reacted with Si particles at a temperature of 62 to 70°C to form polymethylmetacrylate on the surface, a Si cathode material with a Yolk-shell structure. How to manufacture. According to paragraph 1,
In step b), after measuring the charge on the surface of the first polymer coating layer, the surface charge is adjusted through a CTAB solution to induce a surface-selective polymer reaction to occur. Method for manufacturing Si anode material. According to paragraph 1,
Step c) is a method of manufacturing a Si anode material with a yolk-shell structure, which involves heat treatment in an N ₂ atmosphere at a temperature of 500 to 700° C. for 2 to 5 hours. According to paragraph 2,
The CVD is a method of producing a Si cathode material with a yolk-shell structure, wherein CH ₃ CN is deposited. In clause 7,
The CVD is a yolk-shell structure in which CH ₃ CN is deposited by acetonitrile bubbling at a temperature increase rate of 20 to 40° C./min and 900 to 1,100° C. and maintained for 0.5 to 2 hours in an N ₂ atmosphere. Method for manufacturing Si anode material. According to paragraph 2,
A method of manufacturing a Si anode material with a yolk-shell structure, in which curing is performed for 2 to 5 hours at a temperature of 150 to 250 ° C. before proceeding with the CVD. delete delete delete