KR101426521B1 - Negative active material for rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same, wherein the negative electrode active material includes hollow microparticles including hollow and metal oxide nanoparticles surrounding the hollow and forming an external angle.
The negative electrode active material for a lithium secondary battery including the hollow microparticles facilitates diffusion of lithium ions during charge and discharge of lithium ions and controls the volume expansion of the transition metal oxide particles through the internal space to prevent the active material from being separated from the electrode The capacity characteristics and lifetime characteristics of the battery can be remarkably improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a negative active material for a lithium secondary battery, and a lithium secondary battery comprising the negative active material and a lithium secondary battery including the same. BACKGROUND ART [0002]

The present invention relates to a lithium secondary battery which can facilitate the diffusion of lithium ions during charging and discharging and controls the volume expansion of transition metal oxide particles through the internal space to prevent the active material from being separated from the electrode, To a negative electrode active material for a secondary battery and a lithium secondary battery including the same.

The negative electrode of a lithium secondary battery has been developed mainly based on a carbon-based material, and graphite is commercialized and is continuously used commercially. Graphite has advantages such as low discharge voltage, moderate capacity (372 mAh / g) and a certain level of lifetime. However, in order to be used for electric vehicles and electric power storage, . In recent years, tin or silicon-based complexes and transition metal oxides having larger capacity than graphite as an anode active material have attracted attention.

The current graphite material has a theoretical specific capacity of 372 mAh / g and a density of 2.62 g / ml. However, recently developed silicon has a remarkably high theoretical capacity of 4200 mAh / g and a density of 2.33 g / ml. However, due to the rapid volume change (300%, Li ₂ Si ₅ ) due to the insertion and desorption of lithium ions, cracking occurs, and due to the side reaction with the electrolyte due to the desorption of the electrode and the destruction of the SEI layer, Lt; / RTI > The use of transition metal oxides as negative active materials has also resulted in a study of transition metal oxides that are less expensive than silicon and tin and relatively easy to synthesize, although they exhibit short life characteristics due to volumetric changes. Research has been carried out on composite materials coated with carbon on the surfaces of particles such as iron oxide and copper oxide or using graphene sheets. Research on controlling the structure of particles as another technique has also been focused on.

Therefore, one embodiment of the present invention facilitates the diffusion of lithium ions during charging and discharging and controls the volume expansion of the transition metal oxide particles through the internal space to prevent the active material from being separated from the electrodes, A negative electrode active material for a lithium secondary battery and a method of manufacturing the same.

Another embodiment of the present invention is to provide a negative electrode and a lithium secondary battery including the negative electrode active material.

According to an embodiment of the present invention, there is provided a negative active material for a lithium secondary battery comprising a hollow microparticle and a hollow microparticle surrounding the hollow and including metal oxide nanoparticles forming an external angle.

The metal oxide may be an oxide including a metal selected from the group consisting of Fe, Cu, Si, Sn, Ga, Zr, Mo and V. Preferably, the metal oxide is Fe ₂ O ₃ , Fe ₃ O ₄ , it may be selected from _{CuO, SiO 2, SnO, SnO} 2, Ga 2 O 3, ZrO 2, MoO 3, VO 2 , and mixtures thereof.

The metal oxide may have a particle size of 0.01 to 0.1 mu m.

The outer angle of the metal oxide may have an average thickness of 0.2 to 0.5 mu m.

The hollow may have a diameter of 0.6 to 2 탆.

The hollow microparticles may contain a metal oxide in a loading amount of 30 to 50% by weight per unit volume.

The hollow microparticles may be prepared by adsorbing the metal oxide particles on the surface of the hydrogel polymer particles by an electrostatic attraction and then heat-treating them to remove the hydrogel polymer particles.

According to another embodiment of the present invention, a hydrogel polymer particle-containing dispersion prepared by dispersing hydrogel polymer particles in an expandable solvent is mixed with a metal oxide particle-containing dispersion prepared by dispersing metal oxide particles in a dispersion medium, Preparing composite particles of a gel polymer particle core / metal oxide shell, and heat-treating the composite particles of the hydrogel polymer particle core / metal oxide shell to prepare hollow microparticles. ≪ / RTI >

The hydrogel polymer may be selected from the group consisting of polymethacrylic acid, polyacrylic acid, polyacrylamide, polyamine, 2-acrylamido-2-methyl-1-propanesulfonic acid and combinations thereof.

The inflatable solvent may be selected from the group consisting of water, alcohols, and mixtures thereof.

The metal oxide particles may have a zeta potential difference of 20 to 45 mV with the hydrogel polymer.

The metal oxide particle-containing dispersion may further comprise a surfactant selected from the group consisting of dialkyldimethylammonium salts, imidazolium salts, alkyldimethylbenzylammonium salts, alkylmethylammonium bromide, and mixtures thereof.

The surfactant may be included in an amount of 0.5 to 1 part by weight based on 100 parts by weight of the metal oxide particles.

The hydrogel polymer particle-containing dispersion and the metal oxide particle-containing dispersion may be mixed such that the hydrogel polymer particles and the metal oxide particles are in a weight ratio of 1:10 to 1:20.

The manufacturing method may further include a step of adjusting the pH to 6 to 11 during a mixing step of the hydrogel polymer particle-containing dispersion and the metal oxide particle-containing dispersion.

An alcohol may be further added during the mixing step of the hydrogel polymer particle-containing dispersion and the metal oxide particle-containing dispersion.

The heat treatment may be performed at a temperature of 400 to 700 ° C.

According to another embodiment of the present invention, there is provided a negative electrode for a lithium secondary battery comprising the above negative electrode active material for a lithium secondary battery.

According to another embodiment of the present invention, there is provided a lithium secondary battery including the negative electrode.

Other details of the embodiments of the present invention are included in the following detailed description.

The negative electrode active material for a lithium secondary battery including the hollow microparticles facilitates diffusion of lithium ions during charge and discharge of lithium ions and controls the volume expansion of the transition metal oxide particles through the internal space to prevent the active material from being separated from the electrode The capacity characteristics and lifetime characteristics of the battery can be remarkably improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram schematically illustrating a process for producing a negative electrode active material including hollow microparticles according to an embodiment of the present invention. FIG.
FIG. 2A is an optical microscope (OM) photograph of the hydrogel polymer particles obtained immediately after the precipitation polymerization process in Production Example 1, and FIG. 2B is a photograph of the hydrogel polymer particles obtained after the drying process for the precipitation- FIG. 2C is a scanning electron microscopy (SEM) observation image of the polymer particles. FIG. 2C is a graph showing the results of Fourier transform infrared spectroscopy (FT-IR) observation of the hydrogel polymer particles prepared in Production Example 1 Fig.
FIGS. 3A to 3E are photographs showing the expansion behavior of the hydrogel polymer particles prepared in Preparation Example 1 by an optical microscope, and FIG. 3F is a graph showing changes in particle diameter according to pH during the production of the hydrogel polymer particles.
4A is an optical microscope photograph of a composite particle comprising the hydrogel polymer core / nano iron oxide shell prepared in Example 1, and Fig. 4B is a photograph of a composite particle comprising the hydrogel polymer core / nano iron oxide shell prepared in Example 2 2 is an optical microscope photograph of the composite particle.
FIG. 5A is a SEM photograph of a composite particle including a hydrogel polymer core / nano iron oxide shell prepared in Example 1, and FIG. 5B is a SEM image of a composite particle including the hydrogel polymer core / FIG. 5C is a SEM photograph of a section of the composite particle including the hydrogel polymer core / nano iron oxide shell. FIG.
FIG. 6 is a graph showing a result of a thermal gravimetry analysis (TGA) plot of the composite particles including the hydrogel polymer core / nano iron oxide shell prepared in Example 1 during heat treatment,
7A to 7C are cross-sectional views of the composite particles at 200 DEG C, 300 DEG C, and 400 DEG C during the heat treatment process for the composite particles comprising the hydrogel polymer core / nano iron oxide shell prepared in Example 1, (FIB-SEM) using a microscope (Focused Ion Beam-scanning electronic microscopy).
FIG. 8A is a transmission electron microscopy (TEM) photograph showing a cross section of a composite particle including a hydrogel polymer core / nano iron oxide shell prepared in Example 1 before heat treatment, and FIG. 8B is a cross- FIG. 8C is a FIB-SEM photograph of the cross-section of the composite particles after heat treatment. FIG.
FIG. 9 is a graph showing the X-ray diffraction (XRD) patterns observed for the composite particles comprising the hydrogel polymer core / nano iron oxide shell prepared in Example 1 after heat treatment.
10 is a graph showing a result of evaluating charge-discharge characteristics of the negative electrode active material prepared in Example 1. FIG.
11 is a graph showing the results of evaluating the reversible capacitive characteristics of the electrode including the negative electrode active material prepared in Example 1. FIG.
12 is a graph showing the results of evaluating the non-capacity characteristics at various rates of the battery including the negative electrode active material prepared in Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In the present invention, nano-sized transition metal oxide particles are adsorbed on the hydrogel polymer particles by an electrical attraction, and then the hydrogel polymer is removed through heat treatment, and fusion of the transition metal oxide nanoparticles is induced to form metal oxide nanoparticles Hollow microparticles that form a hollow outer shell are prepared and used as an anode active material of a lithium secondary battery to facilitate diffusion of lithium ions during charging and discharging of lithium ions, To thereby improve the capacity characteristics and life characteristics of the lithium secondary battery.

That is, an anode active material for a lithium secondary battery according to an embodiment of the present invention includes a hollow microparticle including a hollow and metal oxide nanoparticles surrounding the hollow and forming an external angle.

As the metal oxide, lithium ions can be reversibly intercalated / deintercalated, and at the same time, the hydrogel polymer particles used in the production and the zeta potential difference of 40 to 45 are electrostatically adsorbed on the surface of the hydrogel polymer particles An oxide containing a metal selected from the group consisting of Fe, Cu, Si, Sn, Ga, Zr, Mo and V can be used. Preferably, a material selected from the group consisting of Fe ₂ O ₃ , Fe ₃ O ₄ , CuO, SiO ₂ , SnO ₂ , Ga ₂ O ₃ , ZrO ₂ , MoO ₃ , VO ₂ , have.

The metal oxide preferably has a particle size of 0.01 to 0.1 mu m, more preferably 0.2 to 0.05 mu m. When the metal oxide has a particle size within the above range, a dense metal oxide shell can be formed.

It is preferable that the metal oxide is included in a loading amount of 30 to 50 wt% per unit volume of the hollow microparticles. Structural stability can be effectively maintained when included in the above range of contents.

In addition, the outer angle of the metal oxide may have an average thickness of 0.2 to 0.5 占 퐉. Within this range, the mobility of lithium movement is improved, and high-rate characteristics can be obtained.

The hollows contained in the hollow microparticles serve as a buffer when the hollow microparticles are applied to the negative electrode active material in the volume expansion of the active material upon charging and discharging. The hollow microparticles preferably have a diameter of 0.6 to 2 탆, Has a diameter of 1 to 1.5 mu m. And exhibits high structural stability when the hollow has a diameter within the above range.

The particle diameter ratio of the hollow and the metal oxide fine particles is preferably 20: 1 to 30: 1.

The negative electrode active material containing the hollow microparticles may be prepared by mixing a hydrogel polymer particle dispersion prepared by dispersing hydrogel polymer particles in an expandable solvent with a metal oxide containing dispersion prepared by dispersing metal oxide particles in a dispersion medium Comprising the steps of: preparing composite particles of a hydrogel polymer particle core / metal oxide shell; and heat treating the composite particles of the hydrogel polymer particle core / metal oxide shell.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram schematically illustrating a process for producing a negative electrode active material including hollow microparticles according to an embodiment of the present invention. FIG. Will be described in detail below with reference to FIG. FIG. 1 is only one example for explaining the present invention, and the present invention is not limited to FIG.

First, the hydrogel polymer particle-containing dispersion is mixed with a metal oxide particle-containing dispersion to prepare a composite particle 10 of hydrogel polymer particle (11) core / metal oxide particle (12) shell (S1).

The hydrogel polymer particle-containing dispersion is prepared by dispersing hydrogel polymer particles (11) in an expandable solvent

As the hydrogel polymer, any polymer capable of exhibiting (+) or (-) charge depending on pH can be used without particular limitation. Specific examples thereof include polyacrylic acid, polyacrylic acid, polyacrylamide, polyamines and 2-acrylamido-2-methyl-1-propanesulfonic acid. 2-methyl-1-propanesulfonic acid, AMPS).

The preparation of the particles using the hydrogel polymer can be carried out according to a conventional polymer particle production method such as a precipitation polymerization method. For example, when the hydrogel polymer particles are prepared by the precipitation polymerization method, they can be prepared by polymerizing and polymerizing hydrogel polymer-forming monomers in a mixed solvent prepared by mixing an organic solvent such as acetonitrile with water. As a specific example, methacrylic acid and ethylene glycol dimethacrylate may be used as monomers in the production of polymethacrylic acid particles. As the polymerization initiator, a hydrophobic initiator may be used. Specific examples thereof include benzoyl peroxide, lauryl peroxide, o-chlorobenzoyl peroxide, o-methoxybenzoyl peroxide butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, dioctanoylperoxide, dide Azo bis (2-methylbutyronitrile), and 2,2-azobis (2,4-dimethylvaleronitrile), which is a group consisting of 2,2-azobisisobutyronitrile, Can be used. At this time, the size of the hydrogel polymer particles 11 to be manufactured can be easily controlled by the mixing ratio of the organic solvent and water and the content of the crosslinking agent.

The hydrogel polymer particles 11 are evaporated during the subsequent heat treatment process to form a hollow. Therefore, it is preferable to use the hydrogel polymer particles 11 having an appropriate particle size according to the intended hollow size. Specifically, it is preferable to use those having particle sizes of (1) to (5) micrometer.

The hydrogel polymer particles (11) are dispersed in a dispersion medium. The dispersion medium used herein is not particularly limited as long as the hydrogel polymer particles are expandable. Specifically, the swellable solvent includes water; Alcohols such as methanol and ethanol; And a mixture thereof can be used.

Since the adsorption of the metal oxide particles 12 to the hydrogel polymer particles 11 is carried out by the electrostatic attraction force, the pH-adjusted buffer solution is used as a solvent so that the hydrogel polymer particles 11 have a proper charge It is possible.

Separately from the hydrogel polymer particle-containing dispersion, metal oxide particles are dispersed in a dispersion medium to prepare a dispersion containing metal oxide particles.

The metal oxide particles 11 are the same as those described above, and it is preferable to select and use appropriate metal oxide nanoparticles according to the surface charge of the hydrogel polymer particles so that adsorption to the surface of the hydrogel polymer particles is possible. Also, the surface potential of the metal oxide nanoparticles can be controlled by using a cationic surfactant. Therefore, it is preferable that the surface potential of the metal oxide nanoparticles is controlled so that the difference in zeta potential between the hydrogel polymer and the metal oxide nanoparticles becomes 20 to 45 by controlling the amount of the cationic surfactant.

The metal oxide particles can be prepared according to a conventional production method, specifically, by dissolving a precursor of the metal oxide in a mixed solvent of polyethylene glycol and water, and reacting the solution with hydrogen peroxide water under a nitrogen atmosphere .

The precursor of the metal oxide may be an alkoxide, a hydroxide, a hydrate, an oxide, a nitride, a nitrate, a carbonate, a sulfate, a metal, or the like including a metal selected from the group consisting of Fe, Cu, Si, Sn, Ga, Zr, Or chloride may be used. One of them may be used alone, or two or more of them may be used in combination. Specifically, ferrous sulfate heptahydrate, ferric sulfate heptahydrate, ferric chloride hexahydrate, and the like can be used.

The dispersion medium may be any solvent selected from the group consisting of water, alcohols, electrolytes, and mixtures thereof, so long as the metal oxide particles are charged.

If the metal oxide particles do not exhibit charge in the dispersion medium, it is possible to make the charge using a surfactant.

The surfactant usable herein may be selected from the group consisting of dialkyldimethylammonium salts, imidazolium salts, alkyldimethylbenzylammonium salts, alkylmethylammonium bromides, and mixtures thereof. Specific examples thereof include cetyltrimethylammonium bromide, n -Dodecyl pyridinium chloride, linear diamine, and mixtures thereof.

In the above, alkyl means C1 to C25 alkyl.

The surfactant serves to increase the dispersibility of the metal oxide particles and to increase the dispersibility of the metal oxide particles. When the surfactant is used in an amount of 100 to 1000 parts by weight based on 100 parts by weight of the metal oxide particles, So that the electrical adsorption can be facilitated.

The hydrogel polymer particle-containing dispersion prepared above and the metal oxide particle-containing dispersion are mixed.

The mixing process may be carried out according to a conventional method. More specifically, a dispersion containing metal oxide particles is dropped into the hydrogel polymer particle-containing dispersion to form the metal oxide particles 11 in the hydrogel polymer particles 12) surface.

When mixing the hydrogel polymer particle-containing dispersion and the metal oxide particle-containing dispersion, the mixing ratio of the two dispersions is such that the hydrogel polymer particles 11 and the metal oxide particles 12 are mixed at a weight ratio of 1: 1 to 1: 2 . When mixed in the above-mentioned content ratio range, a metal oxide shell having a strongest structural characteristic can be obtained.

In addition, since the surface charge of the gel polymer particles exhibits a stronger (-) charge as the pH of the solution becomes more basic, stronger adsorption can be exhibited in a strong base atmosphere. Accordingly, in order to increase the adsorption of the metal oxide particles 12 to the polymer hydrogel particles 11, a strongly basic solution such as NaOH is added to the mixed solution to adjust the pH to 6 to 14, more preferably 11 to 14 . ≪ / RTI >

When the mixing is completed, alcohol such as ethanol is added to shrink the hydrogel polymer particles 11 on which the metal oxide particles 12 are adsorbed to produce the composite particles 10 of the hydrogel polymer particle core / metal oxide shell.

The alcohol serves to help shrinkage of the hydrogel particles therein, and is preferably used in an amount of 100 to 200 parts by weight based on 100 parts by weight of the solvent into which the composite particles are sprayed.

Next, the composite particles 10 of the hydrogel polymer particle core / metal oxide shell prepared above are heat-treated to produce hollow microparticles 20 containing metal oxide nanoparticles (S2).

The heat treatment is preferably performed at a temperature of 400 to 700 ° C. It is preferable that the crystal phase of the iron oxide is not changed when it is carried out in the above temperature range. At this time, it is preferable to heat at a rate of 2 to 5 占 폚 / m.

It is preferable that the heat treatment process is performed for 3 to 5 hours in the temperature range. When the reaction is carried out within the above-mentioned time range, the metal oxide fine particles can be fused to each other without changing the phase of the metal oxide.

More preferably 2 to 5 占 폚 / min, and the heat treatment process is performed at a temperature of 400 to 500 占 폚 for 4 to 5 hours.

The heat treatment is preferably performed in an inert atmosphere such as nitrogen.

 The anode active material including the hollow 21 by the heat treatment process and containing the hollow microparticles 20 surrounding the metal oxide nanoparticles 22 is manufactured.

The method of the present invention can easily adjust the electrical strength between the hydrogel core particles and the metal oxide fine particles according to the concentration of the ionic surfactant, and the amount of the fine particles adsorbed through the adjustment of the electrical strength, The thickness can be adjusted.

The present invention provides a lithium secondary battery having a negative electrode including the negative active material.

The lithium secondary battery includes a negative electrode including the negative electrode active material, a positive electrode including a positive electrode active material, and an electrolyte impregnated into the negative electrode and the positive electrode.

The negative electrode may be prepared by mixing the negative electrode active material, a binder and a solvent to prepare a slurry for forming an anode, directly applying the slurry on the current collector, and drying the slurry, or by casting the slurry for forming a negative electrode on a separate support And then laminating a film obtained by peeling from the support onto a current collector.

The negative electrode active material is the same as that described above, and it is preferable that the negative active material is contained in an amount of 60 to 80% by weight based on the total weight of the composition for forming a negative electrode.

The composition for forming an anode is a negative electrode active material, which is used in combination with the hollow microparticles to form a lithium metal, a metal material that can be alloyed with lithium, a transition metal oxide, a material capable of doping and dedoping lithium, Or a material capable of reversibly intercalating / deintercalating lithium ions, and the like.

The binder functions as a paste for the active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, buffering effect on expansion and contraction of the active material, and the like. Specifically, polyvinylidene fluoride (PvdF) Polytetrafluoroethylene (PTFE), copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), polyacrylonitrile, polymethyl methacrylate Planetary binders such as polymethylmethacrylate; Or an aqueous binder such as carboxymethylcellulose (CMC) or styrene-butadiene rubber (SBR) may be used, and it is preferable to use a binder.

The binder is preferably contained in an amount of 20% by weight or less based on the total weight of the composition for forming a negative electrode.

As the solvent, N-methylpyrrolidone, acetone, tetrahydrofuran, decane and the like can be used. At this time, the content of the cathode active material, the conductive agent, the binder and the solvent can be used at a level commonly used in a lithium secondary battery.

The negative electrode active material composition may further contain a conductive agent, if necessary.

The conductive agent is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Specific examples include carbon materials such as mesoporous carbon, carbon nanotubes, carbon fibers, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; A conductive polymer such as a polyphenylene derivative, or a mixture thereof. Among these, a carbon material having a porous structure capable of providing a large reaction area with a large specific surface area is preferably used.

The collector collects electrons generated by the electrochemical reaction of the active material or supplies electrons necessary for an electrochemical reaction. Specifically, the collector collects electrons generated by the electrochemical reaction of the active material such as stainless steel, aluminum, nickel, iron, copper, titanium, In addition to the resin, a surface of copper or stainless steel treated with carbon, nickel, or titanium may be used. The shape of the current collector is not particularly limited, and specifically, a thin shape, a plate shape, a mesh (grid) shape and a foam (sponge) shape may be mentioned.

 The positive electrode is prepared by mixing a positive electrode active material, a binder, a conductive agent and a solvent in the same manner as the negative electrode to prepare a slurry for forming the positive electrode and then applying the slurry directly to the current collector or cast on a separate support, And then laminating the film to an aluminum current collector.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, at least one of lithium, cobalt, manganese, nickel, or a composite oxide of a metal and lithium in combination thereof can be used.

The conductive agent, the binder, the solvent and the current collector may be the same as those described for the cathode.

As the electrolyte to be charged into the lithium secondary battery, a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous quasicone solvent, or a known solid electrolyte can be used.

In the non-aqueous electrolyte, the non-aqueous organic solvent is not particularly limited, and examples thereof include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and? -Butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Amides such as dimethylformamide and the like can be used. These may be used alone or in combination of two or more, and it is preferable to use a mixed solvent of cyclic carbonate and chain carbonate.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCl, and LiI may be used. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has an appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and the lithium ion can effectively move.

As the solid electrolyte, a gel polymer electrolyte in which an electrolyte is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

The lithium secondary battery having the above-described structure may further include a separator which intercepts electron conduction between the cathode and the anode and is capable of conducting lithium ions.

For example, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more thereof may be used. The separator may be a polyethylene / polypropylene 2 Layered separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc. may be used.

The shape of the lithium secondary battery according to the present invention having such components can be any shape such as a coin type, a button type, a sheet type, a laminate type, a cylindrical type, a flat type, a square type, and the like by a person skilled in the art Designed to fit properly.

Since the lithium secondary battery according to an embodiment of the present invention includes the negative electrode active material including the hollow microparticles, the lithium ion can be easily diffused during charging and discharging of the lithium ion and the volume expansion of the metal oxide particles through the internal space So that the active material can be prevented from desorbing from the electrode. As a result, compared with the lithium battery using the graphite as the negative electrode active material, the capacity characteristics and life characteristics of the battery can be remarkably improved.

Accordingly, the lithium secondary battery of the present invention can be widely used in portable electronic devices such as portable information terminals such as mobile phones and notebook computers, camcorders, small-sized power storage devices for household use, motorcycle, electric vehicles, and hybrid electric vehicles.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Preparation Example 1: Preparation of polymethacrylic acid particles

Polymethacrylic acid particles were prepared by precipitation polymerization.

Specifically, a solvent prepared by adding 12 g of purified water to 68 g of acetonitrile was added with 3.76 g of methacrylic acid, 0.24 g of ethylene glycol dimethacrylate (EGDMA) and 0.22 g of 2,2'-azo-bis-isobutyronitrile To prepare a mixed solution. The resulting mixed solution was placed in a reactor having a capacity of 250 ml and allowed to stand at 80 DEG C for 40 minutes. The resulting particles were washed several times with ethanol and dried at 25 캜 under vacuum to obtain polymethacrylic acid particles.

Production Example 2: Preparation of Iron Oxide Nanoparticles

A mixed solution prepared by dissolving 70 g of polyethylene glycol and 3 g of ferrous sulfate heptahydrate in 140 ml of purified water was placed in a 250 ml capacity reactor equipped with a reflux condenser, a nitrogen purging system and a mechanical stirrer, and then 0.6 ml of 40% hydrogen peroxide The aqueous solution was added and reacted at 50 ° C and pH 13 for 6 hours. At this time, the pH of the mixed solution was adjusted with a 3M aqueous solution of sodium hydroxide. As a result, the obtained magnetic fluid was separated and separated by a magnet, and then purified with purified water several times to obtain iron oxide nanoparticles.

Example 1: Preparation of hollow iron oxide microparticles

0.2 g of the polymethacrylic acid particles prepared in Preparation Example 1 was added to 200 ml of a pH buffer solution (Samchun Pure Chemical Co., LTD.) And stirred for 2 hours to prepare a dispersion containing polymethacrylic acid particles Respectively. Separately, in a round flask, 198 ml of a pH 11 buffer solution and 2 g of cetyltrimethylammonium bromide were added and completely dissolved to prepare a solution. After 0.2 g of the iron oxide nanoparticles prepared in Example 1 was added, the mixture was stirred at 200 rpm and ultrasonically dispersed for 2 hours A dispersion containing iron oxide nanoparticles was prepared.

The dispersion containing the iron oxide nanoparticles was slowly added to the polymethacrylic acid particle-containing dispersion prepared above using a dripping funnel. When the addition was completed, 200 ml of ethanol was added to shrink the polymethacrylic acid particles adsorbed on the iron oxide nanoparticles. The resulting composite particles of the polymethacrylic acid core / iron oxide shell were purified several times with ethanol, and then dried under vacuum at 25 캜. The dried particles were heat-treated at 500 ° C for 5 hours in a nitrogen atmosphere to prepare hollow iron oxide microparticles. The rising temperature during the heat treatment was set at 5 캜 / minute.

Example 2: Preparation of hollow iron oxide microparticles

0.2 g of the polymethacrylic acid particles prepared in Preparation Example 1 was added to 200 ml of a pH 11 buffer solution and stirred for 2 hours to prepare a polymethacrylic acid particle-containing dispersion. Separately, in a round flask, 198 ml of a pH 11 buffer solution and 2 g of cetyltrimethylammonium bromide were added and completely dissolved to prepare a solution. After 0.2 g of the iron oxide nanoparticles prepared in Example 1 was added, the mixture was stirred at 200 rpm and ultrasonically dispersed for 2 hours A dispersion containing iron oxide nanoparticles was prepared.

The dispersion containing the iron oxide nanoparticles was slowly added to the polymethacrylic acid particle-containing dispersion prepared above using a dripping funnel. When the addition was completed, 200 ml of ethanol was added to shrink the polymethacrylic acid particles adsorbed on the iron oxide nanoparticles. The resulting composite particles of the polymethacrylic acid core / iron oxide shell were purified several times with ethanol, and then dried under vacuum at 25 캜. The dried particles were heat-treated at 500 ° C for 5 hours in a nitrogen atmosphere to prepare hollow iron oxide microparticles. The rising temperature during the heat treatment was set at 5 캜 / minute.

Test 1: Evaluation of Hydrogel Polymer Particles

In the preparation of the hydrogel polymer particles in Production Example 1, the hydrogel polymer particles obtained immediately after the precipitation polymerization process and after the drying process were observed using an optical microscope (OM). The hydrogel polymer particles prepared in Preparation Example 1 were subjected to Fourier transform infrared spectroscopy (FT-IR). The results are shown in FIGS. 2A to 2C, respectively.

As can be seen from FIGS. 2A to 2C, it was confirmed that spherical cross-linked hydrogel polymer particles were formed, and that the material prepared through FT-IR was a copolymer of MAA and EGDMA.

The expansion behavior of the hydrogel polymer particles prepared in Preparation Example 1 was observed with an optical microscope (OM), and the results are shown in Figs. 3A to 3E.

As can be seen from FIGS. 3A to 3E, it can be confirmed that the diameter of the hydrogel polymer particles decreases as the pH of the solvent decreases.

The pH of the hydrogel polymer particles is varied by adding an appropriate aqueous hydrochloric acid solution, aqueous sodium hydroxide solution or pH buffer solution (pH 3, pH 5, pH 7, pH 9, pH 11) to vary the pH of the hydrogel polymer particles Respectively. The results are shown in FIG.

From FIG. 3f, it is possible to confirm a rapid particle size change between pH 3 and 5, and the change in diameter from pH 7 to pH 11 is relatively unstable.

Test Example 2: Evaluation of Composite Particles Containing Hydrogel Polymer Core / Nano Iron Oxide Shell and Hollow Microparticles Prepared Therefrom

Composite particles comprising the respective hydrogel polymer core / nano iron oxide shells prepared in Examples 1 and 2 were observed with an optical microscope (OM), and the results are shown in FIGS. 4A and 4B, respectively.

As shown in FIGS. 4A and 4B, a core-shell structure formed by adsorbing iron oxide nanoparticles on a polymer core and an iron oxide shell formed on the surface of shrunken particles at a high density can be confirmed by lowering the pH of the solvent.

The composite particles comprising the hydrogel polymer core / nano iron oxide shell prepared in Example 1 and the surface and cross section thereof were observed by SEM and the results are shown in Figs. 5A to 5C, respectively.

As shown in FIGS. 5A to 5C, it can be seen that the formation of the core-shell structure and the formation of a rugged surface are observed.

The composite grains comprising the hydrogel polymer core / nano iron oxide shell prepared in Example 1 were subjected to a thermal gravimetry analysis (TGA) plot while heating at 30 ° C to 900 ° C at a rate of 5 ° C / min under a nitrogen atmosphere. Were observed. The results are shown in Fig.

As a result of measurement, the mass percentage of the composite particles including the hydrogel polymer core / nano iron oxide shell prepared in Example 1 decreased gradually as the heat treatment temperature was increased up to 350 ° C., but the mass decrease was abruptly observed at about 350 to 450 ° C. Showed almost constant mass% after 450 ° C. Since the TGA plot of the hydrogel polymer prepared in Production Example 1 in which metal oxide particles were not adsorbed exhibits 0 mass% at 450 ° C, all of the hydrogel polymer was removed at 450 ° C, and the mass% (Fe ₃ O ₄ content at 450 ° C: 23.2% by mass).

The cross section of the composite particles at 200 ° C, 300 ° C and 400 ° C during the heat treatment process for the composite particles comprising the hydrogel polymer core / nano iron oxide shell prepared in Example 1 was measured using a Focused Ion Beam scanning electron microscopy (FIB-SEM), and the results are shown in Figs. 7A to 7C, respectively.

From Figs. 7A to 7C, it can be seen that decomposition of the polymer phase takes place from the inside.

In addition, the cross section of the composite particles including the hydrogel polymer core / nano iron oxide shell prepared in Example 1 before heat treatment was observed by transmission electron microscopy (TEM), and after the heat treatment, Sections were observed with TEM and FIB-SEM, respectively. The results are shown in Figs. 8A to 8C.

8A to 8C show that after the heat treatment, the hollow structure is formed.

In addition, X-ray diffraction (XRD) patterns of the composite particles including the hydrogel polymer core / nano iron oxide shell prepared in Example 1 were observed and the results are shown in FIG. 9 .

9, A is the XRD pattern of the composite particles after the heat treatment, and B is the XRD pattern of the composite particles after the heat treatment.

It can be seen from Fig. 9 that the crystallinity is constant even after the heat treatment.

Test Example  3: Electrochemical Characterization

Manufacture of lithium secondary battery

The hollow iron oxide microparticles prepared in the above examples were used as the negative electrode active material, Super P carbon as the conductive material, carboxymethyl cellulose (CMC, manufactured by Daicel Fine Chem Co.) and styrene butadiene rubber (SBR, Zeon Co.) Were mixed at a weight ratio of 60: 20: 10: 10 to prepare a negative electrode active material slurry, which was then applied to a Cu foil, dried and rolled to produce a negative electrode.

As the electrolyte, a mixed solvent of ethylene carbonate and diethyl carbonate (1: 1 by volume, manufactured by Techno Semichem Co., Ltd.) in which 1 M LiPF ₆ was dissolved was used, and a porous polyethylene membrane (Celgard 2300, Thickness: 25 mu m) was used as a separator.

A 2032 coin type cell was prepared using the prepared negative electrode and the electrolyte solution and using lithium foil having a thickness of 1 mm as a counter electrode.

The battery thus prepared was charged and discharged twice at 0.05 C in a potential range of 0.02 V to 3 V at 30 캜 and subjected to a formation step. After charging and discharging at a rate of 100 C at 0.1 C, Life characteristics were measured. The results are shown in Fig. 10 and Fig.

From the results shown in Figs. 10 and 11, it can be seen that the life characteristics are excellent.

After charging and discharging at 0.05 C for evaluation of high rate characteristics, the characteristics were confirmed by charging and discharging 10 times at 0.1 C, 10 times at 0.2 C and 10 C at 0.5 C, respectively. The results are shown in Fig.

From the results of FIG. 12, it can be seen that the high-rate characteristics are excellent.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

Claims (20)

Hollow and
The metal oxide nanoparticles surrounding the hollow and forming an outer angle
And a hollow microparticle comprising the hollow microparticles,
The hollow microparticles are formed by mixing a hydrogel polymer particle-containing dispersion containing hydrogel polymer particles and a metal oxide particle-containing dispersion containing metal oxide particles, followed by heat treatment,
The metal oxide particle-containing dispersion further comprises a surfactant selected from the group consisting of dialkyldimethylammonium salts, imidazolium salts, alkyldimethylbenzylammonium salts, alkylmethylammonium bromide, and mixtures thereof,
Wherein the metal oxide particles have a zeta potential difference of 20 to 40 mV with the hydrogel polymer particles
Negative electrode active material for lithium secondary battery. The method according to claim 1,
Wherein the metal oxide is an oxide including a metal selected from the group consisting of Fe, Cu, Si, Sn, Ga, Zr, Mo and V. The method according to claim 1,
Wherein the metal oxide is selected from the group consisting of Fe ₂ O ₃ , Fe ₃ O ₄ , CuO, SiO ₂ , SnO, SnO ₂ , Ga ₂ O ₃ , ZrO ₂ , MoO ₃ , VO ₂ , Negative active material. The method according to claim 1,
Wherein the metal oxide has a particle size of 0.01 to 0.1 占 퐉. The method according to claim 1,
Wherein an outer angle of the metal oxide has an average thickness of 0.2 to 0.5 占 퐉. The method according to claim 1,
And the hollow has a diameter of 0.6 to 2 占 퐉. The method according to claim 1,
Wherein the hollow microparticles contain a metal oxide in a loading amount of 30 to 50% by weight per unit volume of the negative electrode active material for a lithium secondary battery. The method according to claim 1,
The hollow microparticles are prepared by adsorbing metal oxide particles on the surface of hydrogel polymer particles by electrostatic attraction and then removing the hydrogel polymer particles by heat treatment. A dispersion of hydrogel polymer particles prepared by dispersing hydrogel polymer particles in an expandable solvent is mixed with a dispersion of metal oxide particles prepared by dispersing metal oxide particles in a dispersion medium to form a composite of hydrogel polymer particle core / Producing particles; and
A step of heat treating the composite particles of the hydrogel polymer particle core / metal oxide shell to prepare hollow micro particles
Lt; / RTI >
Wherein the metal oxide particle-containing dispersion further comprises a surfactant selected from the group consisting of dialkyldimethylammonium salts, imidazolium salts, alkyldimethylbenzylammonium salts, alkylmethylammonium bromides, and mixtures thereof.
A method for producing a negative electrode active material for lithium secondary batteries. 10. The method of claim 9,
Wherein the hydrogel polymer is selected from the group consisting of polymethacrylic acid, polyacrylic acid, polyacrylamide, polyamine, and 2-acrylamido-2-methyl-1-propanesulfonic acid. 10. The method of claim 9,
Wherein the expandable solvent is selected from the group consisting of water, alcohols, and mixtures thereof. 10. The method of claim 9,
Wherein the metal oxide particles have a zeta potential difference of 20 to 40 mV with the hydrogel polymer. delete 10. The method of claim 9,
Wherein the surfactant is used in an amount of 0.5 to 1 part by weight based on 100 parts by weight of the metal oxide particles. 10. The method of claim 9,
Wherein the hydrogel polymer particle-containing dispersion and the metal oxide particle-containing dispersion are mixed so that the hydrogel polymer particles and the metal oxide particles are in a weight ratio of 1:10 to 1:20. 10. The method of claim 9,
Further comprising the step of adjusting the pH to 6 to 11 during a mixing step of the hydrogel polymer particle-containing dispersion and the metal oxide particle-containing dispersion. 10. The method of claim 9,
Wherein the alcohol is further added in the mixing step of the hydrogel polymer particle-containing dispersion and the metal oxide particle-containing dispersion liquid. 10. The method of claim 9,
Wherein the heat treatment is performed at a temperature of 400 to 700 ° C. 9. An anode for a lithium secondary battery comprising the anode active material for a lithium secondary battery according to any one of claims 1 to 8. 20. A lithium secondary battery comprising a negative electrode according to claim 19.

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