KR20180035752A - Surface coated porous silicon based anode active material and preparation method thereof - Google Patents

Abstract

According to an embodiment of the present invention, there is provided a porous silicon-based particle including a plurality of pores; And a carbon coating layer on the surface of the porous silicon-based particles, wherein the carbon coating layer covers the entirety of the porous silicon-based particles and includes a portion separated between the carbon-coating layer and the porous silicon-based particles. do.
In the anode active material according to an embodiment of the present invention, the carbon coating layer covers the entire porous silicon-based particles and thus has excellent electrical conductivity, and the reaction can be uniform during charging and discharging. In addition, since the volume expansion of the negative electrode active material is sufficiently absorbed by the spaced apart portions, that is, the pores included in the negative electrode active material, the performance of the secondary battery can be further improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a surface-coated porous silicon-based anode active material and a method for manufacturing the same. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to a surface-coated porous silicon-based anode active material and a method of manufacturing the same.

Recently, a lithium secondary battery, which is attracting attention as a power source for portable electronic devices, has a high energy density by using an organic electrolytic solution and exhibiting a discharge voltage twice higher than that of a conventional battery using an aqueous alkaline solution.

 Although graphite is mainly used as a negative electrode material of a lithium secondary battery, the capacity per unit mass of graphite is as small as 372 mAh / g, making it difficult to increase the capacity of the lithium secondary battery.

(Lithium alloying material) that forms an electrochemical alloy with lithium, such as silicon, tin, and their oxides, which exhibit a higher capacity than graphite, has a high capacity of about 1000 mAh / g or more and a low capacity of 0.3 to 0.5 V Charge / discharge potential, and is attracting attention as an anode active material for a lithium secondary battery.

However, when these materials are electrochemically alloyed with lithium, there arises a problem that the volume of the material is expanded due to a change in the crystal structure. In this case, physical contact loss between the active material of the prepared electrode or the active material and the current collector is generated by coating the powder during charging / discharging, and the capacity of the lithium secondary battery is greatly decreased due to the progress of the charge / discharge cycle.

Further, studies have been made to form pores on the surface and inside of the silicon-based anode active material in order to suppress volume expansion and improve lifetime characteristics when the silicon-based anode active material is used. However, it has been difficult to control the size and uniformity of the pores, and the degree of porosity of the surface and the interior, thereby achieving the performance of a desired battery.

Therefore, in order to increase the capacity of the lithium secondary battery, it is necessary to newly develop a silicone-based material capable of effectively controlling the volume change, and it is possible to control the size and uniformity of the pores of the silicon anode active material, Capacity, efficiency, and cycle life characteristics of the cathode.

Korea Patent Publication No. 2013-0016727

The present invention is intended to solve the above-mentioned problems.

A first object of the present invention is to provide an anode active material capable of improving the life characteristics of a secondary battery by improving electrical contact between particles and particles and capable of improving electric conductivity and uniformly performing a charge / .

A second technical object of the present invention is to provide a method for manufacturing the negative electrode active material.

According to an embodiment of the present invention, there is provided a porous silicon-based particle including a plurality of pores; And a carbon coating layer on the surface of the porous silicon-based particles, wherein the carbon coating layer covers the entirety of the porous silicon-based particles and includes a portion separated between the carbon-coating layer and the porous silicon-based particles. do.

According to an embodiment of the present invention, there is also provided a method of manufacturing a semiconductor device, comprising the steps of: mixing porous silicon particles with a polymer filler; And a second heat treatment of mixing the obtained product with a carbon precursor. The present invention also provides a method for manufacturing a negative electrode active material.

Further, according to an embodiment of the present invention, there is provided a negative electrode and a lithium secondary battery including the negative active material.

According to an embodiment of the present invention, a carbon coating layer is formed on a surface of a porous silicon-based particle including a plurality of pores, the carbon coating layer covers the entire porous silicon-based particles, and the carbon coating layer and the porous silicon- It is possible to improve the electrical contact between the particles and the particles, so that the lifetime characteristics of the secondary battery can be improved. In addition, the carbon coating layer covers the entire porous silicon-based particles and has excellent electric conductivity, so that the reaction can be made uniform during charging and discharging.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a schematic view of a negative electrode active material including a porous silicon-based particle according to an embodiment of the present invention and a carbon coating layer formed on the particle surface.
2 is a SEM photograph of the porous silicon-based particles before the formation of the carbon coating layer prepared in Production Example 1. FIG.
3 is a SEM photograph of the negative electrode active material prepared in Example 1 according to an embodiment of the present invention.
FIG. 4 is a SEM photograph of the negative electrode active material prepared in Comparative Example 1. FIG.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The anode active material according to an embodiment of the present invention includes porous silicon-based particles including a plurality of pores; And a carbon coating layer on the surface of the porous silicon-based particles, wherein the carbon coating layer covers the entire porous silicon-based particles and includes a portion separated between the carbon-coated layer and the porous silicon-based particles.

The negative electrode active material according to an embodiment of the present invention includes a carbon coating layer formed in a thin film shape on the surface of particles and includes a portion separated between the carbon coating layer and the porous silicon based particles, In particular, since the carbon coating layer covers the entire porous silicon-based particles, the electrical conductivity is excellent and the reaction can be uniformized during charging and discharging. In addition, since the volume expansion of the negative electrode active material is sufficiently absorbed by the plurality of pores included in the negative electrode active material, volume expansion can be minimized.

As shown in the schematic diagram of FIG. 1, the negative electrode active material produced by the method according to an embodiment of the present invention includes porous silicon-based particles including a plurality of pores; And a carbon coating layer on the surface of the porous silicon-based particles. The carbon coating layer may be formed to cover the whole of the porous silicon-based particles and may include a portion separated between the carbon-coated layer and the porous silicon-based particles, wherein the spaced portion is a pore formed on the surface of the porous silicon- desirable.

In the anode active material according to an embodiment of the present invention, the carbon coating layer covers the entire porous silicon-based particles and thus has excellent electrical conductivity, and the reaction can be uniform during charging and discharging. In addition, since the volume expansion of the negative electrode active material is sufficiently absorbed by the spaced apart portions, that is, the pores included in the negative electrode active material, the volume expansion is minimized, and the performance of the secondary battery can be further improved.

According to an embodiment of the present invention, the carbon coating layer may have a thickness of 5 nm to 500 nm. When the thickness of the carbon coating layer is less than 5 nm, the effect of increasing the electrical conductivity due to the carbon coating layer is insignificant, and the initial efficiency may be lowered due to high reactivity with the electrolyte solution when the anode active material is applied. If the thickness of the carbon coating layer exceeds 500 nm, the thickness of the carbon coating layer may excessively increase and the resistance of the lithium ion mobility may be impaired.

In addition, the average particle diameter (D ₅₀ ) of the negative electrode active material according to an embodiment of the present invention may be 0.1 μm to 50 μm, preferably 0.5 μm to 20 μm.

If the average particle diameter of the negative electrode active material is less than 0.1 탆, it may be difficult to disperse in the negative electrode active material slurry or aggregation of the negative electrode active material in the electrode. If the average particle diameter exceeds 50 탆, One reaction is difficult, so that the lifetime characteristics and the thickness expansion inhibition characteristics can be greatly reduced.

In the present invention, the average particle diameter of the particles can be defined as the particle diameter at the 50% of the particle diameter distribution of the particles. The average particle diameter (D ₅₀ ) of the particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of a particle diameter of several millimeters from a submicron region, resulting in high reproducibility and high degradability.

The specific surface area (BET-SSA) of the negative electrode active material according to an embodiment of the present invention is preferably from 2 m 2 / g to 80 m 2 / g, and the negative electrode active material satisfying the specific surface area in the above range is applied to a lithium secondary battery , The rate characteristics of the lithium secondary battery can be improved.

If the specific surface area of the negative electrode active material is more than 2 m 2 / g, it may be difficult to control the side reaction with the electrolyte due to its wide specific surface area. If the specific surface area is less than 80 m 2 / g, sufficient pores are not formed in the negative electrode active material, It may be difficult to effectively accommodate the volume expansion during charging / discharging of the battery.

According to an embodiment of the present invention, the specific surface area of the negative electrode active material may be measured by a BET (Brunauer-Emmett-Teller) method. For example, it can be measured by a BET 6-point method by a nitrogen gas adsorption / distribution method using a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini).

The negative electrode active material of the present invention may further include a graphite based material, and the graphite based material may include at least one selected from the group consisting of natural graphite, artificial graphite and mesocarbon microbeads (MCMB). The content of the further graphite-based material may be, for example, 30 wt% to 99 wt%, preferably 50 wt% to 98 wt%, based on the total weight of the negative electrode active material.

The present invention can provide a method of manufacturing the negative electrode active material.

A method of manufacturing an anode active material according to an embodiment of the present invention includes: a first heat treatment step (I) of mixing a porous silicon-based particle with a polymer filler; And a second heat treatment (Step II) of mixing the obtained product with a carbon precursor.

Generally, in the case of porous silicon-based particles containing a large number of pores, particularly porous silicon-based particles existing on the surface of the particles, the area of the portion where the particles and the particles come into contact with each other is reduced due to the pores formed on the surface of the particles, The electrical contactability can be lowered.

Accordingly, in the present invention, the polymeric filler is filled in the pores present in the porous silicon-based particles by mixing the porous silicon-based particles with the polymer filler and performing a first heat treatment (Step I), and the obtained product is mixed with the carbon precursor , A smooth carbon coating layer including pores (pores) spaced between the carbon coating layer and the porous silicon-based particles can be formed while pyrolyzing and volatilizing the polymer filler that has been filled in the pores with the monomer Step II).

Specifically, according to the method of manufacturing an anode active material according to an embodiment of the present invention, the step I may include a step of mixing the porous silicon-based particles with a polymer filler and performing a primary heat treatment.

The step I may be a step for filling the filler into the pores of the porous silicon-based particles by the first heat treatment.

The polymer filler that can be used according to one embodiment of the present invention is not particularly limited as long as the pyrolysis temperature of the polymer precursor and the carbonization temperature of the carbon precursor have a similar range. For example, the polymer filler may include a polyacrylate polymer.

More specifically, the polyacrylate-based polymer may be selected from the group consisting of polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA), and polybutyl methacrylate (PBMA) , Or a mixture of two or more thereof, and most preferably polymethyl methacrylate may be used.

The primary heat treatment may be performed at a temperature higher than the melting temperature of the filler so that the filler can penetrate into the pores while being melted.

Specifically, when a polymethacrylate-based polymer is used as the polymer filler, the first heat treatment may be performed at a temperature of 150 ° C or higher, preferably 150 ° C to 500 ° C, 20 hours, preferably 30 minutes to 10 hours.

In the method of manufacturing an anode active material according to an embodiment of the present invention, the amount of the filler to be used may vary depending on the internal porosity of the porous silicon-based particles. For example, the density of the silicon- It may be an amount satisfying the porosity.

When the amount of the polymer filler is excessively used in comparison with the pores existing in the porous silicone-based particles, the filler is melted to excess not only the pores but also the surface of the porous silicon-based particles, or the entire pores can not be filled, . ≪ / RTI > As a result, the electrical contact between the particles and the particles may be lowered and the lifetime characteristics may be deteriorated. In addition, the reaction can not be uniformed during charging / discharging, and the resistance of the lithium ion may be increased due to the obstruction of the lithium ion mobility.

According to an embodiment of the present invention, the internal porosity of the porous silicon-based particles is preferably 5% to 90% with respect to the total volume of the porous silicon-based particles.

When the internal porosity of the porous silicon-based particles is less than 5%, the volume expansion during charging and discharging may not be suppressed. When the porosity exceeds 90%, the mechanical strength of the porous silicon-based particles is lowered due to a large amount of pores, Slurry mixing, pressing after coating, etc.), the porous silicon-based particles may be destroyed.

Here, the porosity can be defined as follows:

Porosity = pore volume per unit mass / (specific volume + pore volume per unit mass)

The porosity can be measured by, for example, a BET (Brunauer-Emmett-Teller) measurement method or a Hg porosimetry method according to an embodiment of the present invention without particular limitation.

In the method for manufacturing the negative electrode active material according to an embodiment of the present invention, the porous silicon-based particles may be manufactured by using commercially available porous silicon-based particles, or by preparing porous silicon-based particles having pores formed on the surface, .

Specifically, the step of preparing the porous silicon-based particles includes, for example, mixing a fluorine-based solution with a metal precursor solution, and then introducing the silicon-based particles into the mixed solution to deposit metal particles on the surface of the silicon-based particles (step ii) of contacting the silicon particles with the metal particles deposited thereon with an etching solution (step ii), and removing the metal particles by contacting the etched silicon particles themselves with a metal removing solution (step iii) .

According to one embodiment of the present invention, the silicon-based particles are not particularly limited as long as the content of x satisfies the above-described range, but SiO _x (when 0? _X ? 2) particles can be used.

More specifically, when Si or SiO ₂ particles are used, or SiO _x (where 0 <x <2) is used, the molar ratio of Si and SiO ₂ is controlled to be mixed and then mechanically alloyed , SiO _x can be obtained.

Here, mechanical alloying is the application of a mechanical force to produce a mixed composite of uniform composition. Such a mechanical alloying method is not particularly limited, but can be performed using, for example, a Mechano fusion apparatus known in the art. Examples of the mechanofusion apparatus include a high energy ball mill apparatus, a planetary mill apparatus, a stirred ball mill apparatus, a vibrating mill apparatus, and the like. Of these, mechanical alloying may be performed in a high energy ball mill, but is not limited thereto. When 0 <x <2 in the SiO _x particles produced by the above method, the content of x may vary depending on the amount of Si and SiO ₂ mixed in the mechanical alloying.

Meanwhile, the average particle size (D ₅₀ ) of the porous silicon-based particles may be 100 nm to 20 탆.

When the average particle diameter of the porous silicon-based particles is less than 100 nm, dispersion in the negative electrode active material slurry may be difficult, and when the average particle diameter exceeds 20 m, expansion of particles due to charging of lithium ions becomes severe, The bondability between the particles and the bondability between the particles and the current collector are deteriorated and the lifetime characteristics can be greatly reduced.

Specifically, in the method of manufacturing an anode active material according to an embodiment of the present invention, in step i) of the porous silicon-based particles, the fluorine-based solution is mixed with the metal precursor solution, and then the silicon- And electrodepositing the metal particles on the surface of the silicon-based particles.

At this time, the fluorine-based solution causes the silicon-based particles to emit electrons. The electrons emitted are absorbed by the metal ions in the solution, and the metal ions are reduced and electrodeposited on the surface of the silicon-based particles. Once the metal particles are electrodeposited on the surface of the silicon-based particles, the metal particles themselves become the catalytic sites and the continuous electrodeposition occurs.

The fluorine-based solution may be at least one selected from the group consisting of hydrogen fluoride (HF), silicic fluoride, and ammonium fluoride (NH ₄ F). The metal precursor solution may be silver (Ag) , Platinum (Pt), and copper (Cu).

According to an embodiment of the present invention, the fluorine-based solution and the metal precursor solution may be mixed at a weight ratio of 10 to 90: 90 to 10. When the fluorine-based solution is mixed in an amount of less than 10 parts by weight, the amount of the metal particles electrodeposited on the surface of the silicon-based particles is small and the reaction rate is very low, which may result in a long manufacturing time. In addition, when the fluorine-based solution is mixed in a ratio of more than 90 wt%, the rate of electrodeposition of the metal particles on the surface of the silicon-based particles is very high, so that uniform and small-sized metal particles can not be deposited on the silicon-based particles.

Further, the amount of the metal particles electrodeposited on the silicon-based particles can be controlled according to the concentration of the fluorine-based solution and the contact time between the silicon-based particles and the metal precursor solution. The silicon-based particles may be added in an amount of 0.001 to 50 parts by weight based on 100 parts by weight of the mixed solution of the fluorine-based solution and the metal precursor solution.

In the method of manufacturing an anode active material according to an embodiment of the present invention, in the step of producing the porous silicon-based particles, the step ii) may be a step of etching the silicon-based particles electrodeposited with the metal particles, have.

That is, the step of contacting the silicon-based particles deposited with the metal particles obtained in step i) with the etching solution to etch the silicon-based particles to form pores on the surface or the surface and inside of the silicon-based particles. Through this etching process, nanopores, mesopores and macropores can be formed.

The etching of the silicon-based particles is as follows. For example, the metal particles are oxidized to become metal ions by H ₂ O ₂ , and at the interface between the silicon-based particles and the metal particles, the silicon-based particles are continuously dissolved while transferring electrons to the metal particles. Reduction of oxidized metal ions occurs in electrodeposited metal particles. In this way, the silicon-based particles in contact with the metal particles can be continuously etched to form at least a honeycomb-like porous structure on the surface. By controlling the type of metal particles and the reaction time, the pore size Can be adjusted.

The etching solution may be a mixed solution of a hydrogen fluoride (HF) solution and a hydrogen peroxide (H ₂ O ₂ ) solution. The amount of the hydrogen fluoride solution included may vary depending on the degree of etching. The hydrogen fluoride (HF) Solution and a hydrogen peroxide (H ₂ O ₂ ) solution may be mixed at a weight ratio of 10 to 90:90 to 10. At this time, the content of H ₂ O ₂ plays an important role in pore formation in the silicon-based particles.

Further, the etching may be performed for 30 minutes to 24 hours depending on the concentration of the etching solution. When the etching is performed for less than 30 minutes, pore generation is insufficient. When the etching is performed for more than 24 hours, the silicon particles are excessively etched and the mechanical properties of the active material deteriorate.

In the method for manufacturing an anode active material according to an embodiment of the present invention, in the step of producing the porous silicon-based particles, the step iii) includes a step of removing the metal particles by contacting the etched silicon- .

The metal removing solution may include at least one selected from the group consisting of nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), and hydrochloric acid (HCl).

In the method of producing the porous silicon-based particles according to an embodiment of the present invention, the etching method may form pores without changing the crystal structure of the silicon-based particles.

According to the method of manufacturing an anode active material according to an embodiment of the present invention, the step II may include a step of mixing the product obtained in the step I with a carbon precursor and then performing a secondary heat treatment.

In the step II, the polymer filler, which has been filled in the pores, is volatilized by the thermal decomposition of the monomer by the secondary heat treatment, and at the same time, the carbon coating layer can be formed on the surface of the porous silicon-based particles.

The temperature of the second heat treatment may be higher than the temperature range in which the polymer filler is pyrolyzed and volatilized by the monomer, and may be performed at a temperature range of, for example, 300 ° C to 1300 ° C, preferably 400 ° C to 1000 ° C And the heat treatment time may be about 20 minutes to 20 hours, preferably 30 minutes to 10 hours.

If the temperature of the second heat treatment is less than the above range, the polymer filler may not be completely volatilized due to insufficient pyrolysis of the monomer, so that the internal porosity decreases due to the presence of the polymer filler, have. In addition, if it exceeds the above range, it is not preferable because there is no economic benefit due to excess temperature or time. In some cases, the crystal structure of the particles may change due to high temperature even though the pore structure of the porous silicon-based particles is not changed.

The secondary heat treatment is preferably performed in an inert atmosphere in which a nitrogen gas, an argon gas, a helium gas, a krypton gas, or a xenon gas is present.

The carbon precursor which can be used according to an embodiment of the present invention may be any one that can generate carbon by heat treatment. For example, the carbon precursor may be a carbon-containing gas, amorphous or low-crystalline carbon.

Specifically, saccharides such as glucose, fructose, galactose, maltose, lactose or sucrose; Resins such as phenol resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan resin, cellulose resin, epoxy resin, polystyrene resin, resorcinol resin or fluoroglucinol resin; And a mixture of two or more selected from the group consisting of coal-based pitch, petroleum pitch, tar, low-molecular-weight heavy oil, and the like.

More preferably, saccharides such as glucose, fructose, galactose, maltose, lactose or sucrose may be preferable, and sucrose, which is carbonizable as a carbon precursor in a range similar to the thermal decomposition temperature of the polymer filler, is preferable . Since the temperature of the saccharide such as sucrose is very similar to the temperature at which the polymer filler such as polymethyl methacrylate pyrolyzes and volatilizes, the polymer filler is volatilized while being thermally decomposed by the monomer, and at the same time, A carbon coating layer can be formed on the surface.

If the polymeric filler is pyrolyzed and volatilized before the carbonization temperature of the carbon precursor, the carbon precursor may fill the pores of the particles, so that the desired polymeric filler of the present invention may not be effective. Further, even if the carbon precursor has a carbonization temperature higher than the carbonization temperature, if the polymer filler is present inside the particles, it may block pores.

Therefore, according to an embodiment of the present invention, it is most preferable that the thermal decomposition temperature of the polymer filler is similar to the carbonization temperature of the carbon precursor.

According to an embodiment of the present invention, the difference between the pyrolysis temperature of the polymer filler and the carbonization temperature of the carbon precursor is preferably 100 ° C or lower.

The carbon coating layer may be carbonized using, for example, the amorphous carbon precursor. The coating method can be used both dry and wet mixing. In addition, a vapor deposition method such as a chemical vapor deposition (CVD) method using a gas including carbon such as methane, ethane, propane, ethylene, acetylene, etc. may also be used.

The present invention also provides a negative electrode comprising the negative active material.

The cathode may be manufactured by a manufacturing method commonly used in the art. For example, a negative electrode may be manufactured by preparing a slurry by mixing and stirring a binder and a solvent, if necessary, a conductive agent and a dispersant in an anode active material according to an embodiment of the present invention, applying the slurry to a current collector, .

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and polymers in which hydrogen is substituted with Li, Na, or Ca, or Various kinds of binder polymers such as various copolymers can be used. As the solvent, N-methylpyrrolidone, acetone, water and the like can be used.

The conductive agent is not particularly limited as long as it has electrical conductivity without causing any chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The cathode active material, the conductive agent, the binder and the solvent are mixed to prepare a slurry, which is directly coated on the metal current collector or cast on a separate support, and the cathode active material film, which is peeled from the support, The positive electrode can be manufactured by lamination to the current collector.

The separation membrane is interposed between the cathode and the anode, and an insulating thin film having high ion permeability and mechanical strength is used. The current collector, the electrode active material, the conductive material, the binder, the filler, the separator, the electrolyte, the lithium salt, and the like are well known in the art, and a detailed description thereof will be omitted herein.

A battery current collector is formed with a separator interposed between the positive electrode and the negative electrode. The battery current collector is wound or folded into a cylindrical battery case or a prismatic battery case, and then an electrolyte is injected to complete the secondary battery. Alternatively, the battery current collector may be laminated in a bi-cellular structure, then impregnated with an electrolyte, and the resulting product is sealed in a pouch to complete the secondary battery.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells. Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric power storage systems, and the like.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Preparation Example 1: Preparation of porous Si particles

&Lt; Step (i): Preparation of Si-MxSiy alloy powder using metal (M) and Si >

24 mol% of high-purity Ti powder and 76 mol% of Si were used. Powder and balls were filled in a SPEX mill filled with Ar and milled for 15 hours Si-TiSi ₂ alloy powder.

<Step (ii): Step of removing TiSi ₂ to obtain porous silicon-based particles by etching and mixing the Si-TiSi ₂ alloy powder with an etching solution by mixing and stirring>

The Si-TiSi ₂ alloy powder obtained in the above step (i) was heat-treated at about 800 ° C, mixed with 1M hydrogen fluoride, mixed and stirred, and etched for 1 hour, sufficiently washed and filtered. The filtered product was dried in a drying oven at 100 DEG C for 2 hours to obtain porous Si particles.

Example 1: Preparation of negative electrode active material

Step I): Step of filling PMMA inside the pores

After the porous Si particles and the polymethacrylate (PMMA) are mixed, the PMMA is infiltrated into the pores of the porous Si particles by performing heat treatment at a temperature at which the PMMA can be melted, that is, at about 160 ° C for 1 hour Lt; / RTI &gt; The amount of the PMMA was such that the pore size of the porous Si particles prepared in Preparation Example 1 was 48% by using the true density of the porous Si particles and the density of PMMA (1.18 g / cc) Respectively.

Step II): volatilization by thermal decomposition of PMMA and formation of carbon coating layer

Porous Si particles and sucrose solution containing PMMA obtained in the step I) were mixed in a ratio of 65:45 parts by weight to disperse the porous silicon particles in a sucrose solution and heat-treated at about 500 ° C for 3 hours under an argon atmosphere to obtain an anode active material . At this time, the thickness of the carbon coating layer was about 120 nm.

Comparative Example 1

The porous Si particles and sucrose solution obtained in Preparation Example 1 were mixed in a ratio of 65:45 parts by weight to disperse the porous silicon particles in a sucrose solution and heat-treated at about 500 ° C for 3 hours in an argon atmosphere to obtain an anode active material. The thickness of the carbon coating layer was about 80 nm.

&Lt; Production of lithium secondary battery >

Example 2

Carbon black conductive agent, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) were mixed in a weight ratio of 40:60 by mixing the negative electrode active material and spherical natural graphite prepared in Example 1 as a negative electrode active material, ) Were mixed in a weight ratio of 97: 1: 1: 1, and these were mixed with distilled water as a solvent to prepare a slurry. The slurry thus prepared was coated on one surface of the copper current collector to a thickness of 30 탆 and dried and densified at an electrode density of 1.6 g / cc After rolling, the anode was punched to a predetermined size.

10% by weight of fluoroethylene carbonate was added to a mixed solvent containing an organic solvent prepared by mixing ethylene carbonate and diethyl carbonate at a weight ratio of 30:70 and 1.0 M of LiPF ₆ based on the total amount of the electrolytic solution, Thereby preparing an electrolytic solution.

A lithium metal foil was used as a counter electrode. A polyolefin separator was interposed between both electrodes, and the electrolyte was injected into the coin type half cell.

Comparative Example 2

A coin-shaped half-cell was fabricated in the same manner as in Example 2, except that the negative active material prepared in Comparative Example 1 was used in place of the negative active material prepared in Example 1 above.

Comparative Example 3

A coin-shaped half-cell was fabricated in the same manner as in Example 2, except that the negative active material prepared in Preparation Example 1 was used in place of the negative active material prepared in Example 1 above.

Experimental Example 1

<SEM micrograph>

The negative electrode active material obtained in Preparation Example 1, Example 1 and Comparative Example 1 was confirmed by scanning electron microscope (SEM) photograph. The results are shown in Figs.

Specifically, FIG. 2 is a SEM photograph of the surface of the porous Si particles prepared in Production Example 1. FIG. 2, it can be seen that the surface of the porous silicon-based particles prepared in Production Example 1 contains a large number of pores.

3 and 4 are SEM photographs of the surface of the negative electrode active material including the carbon coating layer according to Example 1 and Comparative Example 1, respectively.

As shown in FIG. 3, unlike the SEM image of FIG. 2 showing the state before the carbon coating layer is formed, it can be seen that the carbon coating layer is formed in a thin film shape while completely covering the porous silicon-based particles without forming pores on the surface of the anode active material. It can be seen that the shape of pores hollowed out through the carbon coating layer is reflected. The pores may be spaced apart portions between the carbon coating layer and the porous silicon-based particles.

3, PMMA was used as the polymer filler in the negative electrode active material prepared in Example 1, but PMMA which had been filled in the pores after the carbon coating layer was formed was pyrolyzed and volatilized by the secondary heat treatment, It can be guessed that pores are formed again.

4, unlike the SEM image of FIG. 3 after the formation of the carbon coating layer, the carbon coating layer is not formed so as to cover the entire porous silicon-based particles in the form of a thin film, but is similar to the porous Si particles of Production Example 1 It can be confirmed that it is coated in the form of

That is, the SEM photograph of FIG. 4 shows that the carbon coating layer of the negative electrode active material retains the appearance of the porous Si particles produced in Production Example 1 without including the portion (surface pore portion) spaced between the carbon coating layer and the porous silicon- .

Experimental Example 2: Capacity characteristics

The capacity and charge / discharge cycle capacity of the lithium secondary battery prepared in Example 2 and Comparative Examples 2 and 3 were investigated in terms of the voltage level (V) and the capacities of the batteries prepared in Example 2 and Comparative Examples 2 and 3 The lithium secondary battery was charged at a constant current (CC) condition of 0.1 C and a constant current (CC) condition of 5 mV at a temperature of 23 캜 at 23 캜 and then charged until the current reached 0.005 C under a constant voltage condition (CV) CC) conditions. After the discharge was performed to 1.5V, The dose was measured . This was repeated with 1 to 49 cycles. The results are shown in Table 1 below.

Experimental Example 2: Measurement of life characteristic and thickness change rate

The life characteristics of the lithium secondary battery manufactured in Example 2 and Comparative Examples 2 and 3 were such that the ratio of the 49th cycle discharge capacity to the first cycle discharge capacity was measured. The thickness change rate was measured by dividing the lithium secondary battery in the charged state at the 50th cycle and comparing the electrode thickness with the electrode thickness before the first cycle. The results are shown in Table 1 below.

Capacity (mAh) life span (%) Thickness change ratio (%) Example 2 (Example 1) 503 98 56 Comparative Example 2 (Comparative Example 1) 502 91 75 Comparative Example 3 (Production Example 1) 508 84 82

(Electrode thickness in the 50th cycle in the charged state-electrode thickness before the first cycle) / electrode thickness before the first cycle X 100 (thickness of the electrode before the first cycle): life characteristic: (49th cycle discharge capacity / first cycle discharge capacity)

As can be seen from Table 1, the lithium secondary battery of Example 2 using the negative electrode active material in which the carbon coating layer was formed on the surface of the porous silicon-based particles using the polymer filler exhibited excellent capacity and life characteristics.

On the other hand, in the lithium secondary battery of Comparative Example 2 using the negative electrode active material in which the carbon coating layer was formed using only sucrose without using the polymer filler even in the case of including the carbon coating layer, the comparative example using the negative active material containing no carbon coating layer 3, the capacity and lifetime characteristics were better than those of the lithium secondary battery of Example 2. However,

Specifically, the capacity of the lithium secondary battery of Example 2 was about 1 mAh higher than that of the lithium secondary battery of Comparative Example 2, the lifetime was increased by about 7%, and compared with Comparative Example 3 which did not include the carbon coating layer The capacity increased by about 5 mAh, and the lifetime increased by about 16%.

This is presumably because the carbon coating layer covers the entire porous silicon-based particles and thus has excellent electrical conductivity and uniformity of the reaction during charging and discharging, thereby improving capacity and lifetime characteristics.

As for the thickness change ratio, the thickness of the lithium secondary battery of Example 2 was about 56% before the first cycle, and the electrode thickness in the 50th cycle in the charged state - electrode thickness before the first cycle) was about 56% And 30% to 46%, respectively.

It can be predicted that the volume expansion is minimized by the porous pores of the porous silicon-based particles included in the anode active material and the pores and the particles, which are the separated portions of the carbon coating layer.

Claims (11)

Mixing the porous silicone-based particles with a polymer filler to perform a primary heat treatment; And
And a second heat treatment by mixing the obtained product with a carbon precursor,
Wherein the primary heat treatment is performed at a temperature higher than the melting temperature of the polymer filler.
The method according to claim 1,
Wherein the polymer filler comprises a polyacrylate-based polymer.
The method of claim 2,
The polyacrylate polymer may be selected from the group consisting of polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA), and polybutyl methacrylate (PBMA) Or a mixture of two or more selected from the above.
The method according to claim 1,
Wherein the first heat treatment is performed in a temperature range of 150 ° C to 500 ° C.
The method according to claim 1,
Wherein the polymeric filler is filled in the pores of the porous silicon-based particles by the first heat treatment.
The method according to claim 1,
Wherein the polymeric filler is thermally decomposed and volatilized by the secondary heat treatment to form a carbon coating layer on the surface of the porous silicon-based particles.
The method according to claim 1,
Wherein the secondary heat treatment is performed in a temperature range of 300 ° C to 1300 ° C.
The method according to claim 1,
Wherein the difference between the pyrolysis temperature of the polymer filler and the carbonization temperature of the carbon precursor is 100 ° C or less.
The method according to claim 1,
Wherein the carbon precursor is a carbon-containing gas, amorphous or low-crystalline carbon.
The method of claim 6,
Wherein the carbon coating layer is formed by a method of carbonizing using an amorphous carbon precursor or a chemical vapor deposition method using a gas containing carbon.
The method of claim 9,
The amorphous or low crystalline carbon may be selected from the group consisting of glucose, fructose, galactose, maltose, lactose, sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan resin, Characterized in that it is any one selected from the group consisting of a resin, a resorcinol resin, a fluoroglucinol resin, a coal pitch, a petroleum pitch, tar and a low molecular weight heavy oil or a mixture of two or more thereof A method for producing an active material.

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