KR20130016727A - Negative active material for rechargeable lithium battery, method of preparing the same, and negative electrode and rechargeable lithium battery including the same - Google Patents

Abstract

PURPOSE: A lithium secondary battery with improved lifetime by suppressing the volume change of a negative electrode active material. CONSTITUTION: A negative electrode active material(1) for a lithium secondary battery comprises: a core(2) which comprises a porous silicon particle or a porous silicon-based compound particle; and a coating layer which surrounds the core. The coating layer comprises a carbon particle(3); and amorphous carbon or low crystalline carbon(4) which binds the carbon particle. The core has an average porous size of 2nm-3microns, a porosity of 2-90 volume%, and an average particle size of 0.3-30 microns.

Description

A negative active material for a lithium secondary battery, a method for manufacturing the same, and a negative electrode and a lithium secondary battery including the same.

The present disclosure relates to a negative electrode active material for a lithium secondary battery, a manufacturing method thereof, and a negative electrode and a lithium secondary battery including the same.

BACKGROUND ART [0002] Lithium secondary batteries have been widely used as power sources for electronic devices because they have high voltage and high energy density. Recently, as the performance of electronic devices has been improved and applications of electric vehicles have been expanded, energy density of lithium secondary batteries has been increasingly demanded.

At present, carbon materials including graphite are mainly used as an anode active material composing a cathode of a lithium secondary battery. However, since graphite has a theoretical capacity of about 372 mAh / g corresponding to LiC ₆ , it is necessary to develop a high-capacity negative electrode active material in order to further increase the energy density of the lithium secondary battery.

In order to meet such a demand, metal or metal compounds such as Si that form an alloy with lithium have been studied. However, due to the volume expansion due to the alloying with lithium, cracks are formed in the active material, the lithium battery is undifferentiated, and peeling occurs from the current collector to deteriorate the charge-discharge cycle characteristics.

An embodiment of the present invention is to provide a negative electrode active material for a lithium secondary battery having improved life characteristics of a battery by suppressing a volume change of an active material.

Another embodiment of the present invention is to provide a method of manufacturing the negative electrode active material for the lithium secondary battery.

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

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

One embodiment of the present invention is a method of manufacturing a porous silicon-based compound particle, comprising: a core comprising porous silicon particles or porous silicon-based compound particles; And a coating layer surrounding the core, the coating layer comprising carbon particles; And an amorphous carbon or a low-crystalline carbon which binds the carbon particles, and a negative electrode active material for a lithium secondary battery.

The porous silicon-based compound particles may be represented by the following formula (1).

[Formula 1]

M _y Si

(In the formula (1), M includes at least one element of the elements of Groups 1 to 16, and y is 0.001 to 0.4.)

M in Formula 1 is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Ta, W, Re , Os, Mg, Ca, B, P, Al, Ge, Sn, Sb, Bi, Li, O or a combination thereof.

The porous silicon particles or the porous silicon-based compound particles can be obtained by etching a silicon-based alloy represented by Formula 2 below.

[Formula 2]

M ' _x Si

Wherein M 'comprises at least one element selected from the group consisting of elements of Groups 1 to 16, and x is 0.01 to 1.0.

The silicon-based alloy represented by Formula 2 may include Si phase, Si and M '-containing compound phase, and M' phase.

The core may have an average pore size of 2 nm to 3 μm and a porosity of 2 to 90% by volume, and may have an average particle size of 0.3 to 30 μm.

The carbon particles may have an average particle size of 0.1 to 20 mu m.

The carbon particles may include crystalline graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, Ketjen black, super P, graphene, fibrous carbon or combinations thereof , The crystalline natural graphite may be obtained by separating or pulverizing the ground graphite, and the fibrous carbon may be a polyacrylonitrile-based carbon fiber, rayon-based carbon fiber, pitch-based carbon fiber, carbon nanotube, vapor grown carbon fiber ), Or a combination thereof.

The shape of the carbon particles may be amorphous, scaly, plate, spherical, fibrous, or a mixture thereof.

The amorphous carbon or the low crystalline carbon may be at least one selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, A styrene resin, a styrene resin, a polyimide resin, an epoxy resin, a vinyl chloride resin, citric acid, stearic acid, polyfluorovinylidene, carboxymethylcellulose (CMC), hydroxypropylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, glucose, gelatin, sugars, coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar, low molecular weight heavy oils or combinations thereof ≪ / RTI >

The ratio of the average particle size size of the carbon particles to the average particle size of the core may be 0.001 to 0.7.

The average thickness of the coating layer may be 0.1 to 30 탆.

The amorphous carbon or low-crystalline carbon may be contained in an amount of 0.1 to 90 parts by weight based on 100 parts by weight of the carbon particles.

The amorphous carbon or the low-crystalline carbon may further surround the coating layer.

Another embodiment of the present invention is a method for producing a porous silicon-based compound, comprising the steps of: preparing porous silicon particles or porous silicon-based compound particles; Coating the surfaces of the porous silicon particles or the porous silicon-based compound particles with an amorphous carbon precursor or a low-crystalline carbon precursor and carbon particles to produce composite particles; And heat treating the composite particles. The present invention also provides a method for manufacturing a negative electrode active material for a lithium secondary battery.

The porous silicon-based compound particles may be represented by the following formula (1).

[Formula 1]

M _y Si

(In the formula (1), M includes at least one element of the elements of Groups 1 to 16, and y is 0.001 to 0.4.)

The step of preparing the porous silicon particles or the porous silicon-based compound particles may include a step of etching a silicon-based alloy represented by Formula 2 below.

[Formula 2]

M ' _x Si

Wherein M 'comprises at least one element selected from the group consisting of elements of Groups 1 to 16, and x is 0.01 to 1.0.

The silicon-based alloy represented by Formula 2 may include an Si phase, a Si and M '-containing compound phase, and an M' phase, and the porous silicon particles or the porous silicon-based compound particles may include the Si and M ' And the M 'phase.

The step of preparing the porous silicon particles or the porous silicon-based compound particles may further include a step of performing a heat treatment before the etching step, and the heat treatment may be performed at a temperature of 200 to 1000 ° C.

The step of preparing the composite particles may include: preparing a mixture by mixing the porous silicon particles or the porous silicon-based compound particles, carbon particles, and an amorphous carbon precursor or a low-crystalline carbon precursor; And carrying out a coating process using the mixture, including a mechanochemical method, a spray drying method, a fluidized bed coating method, a precipitation method, or a sputtering method.

The spray drying method may be carried out by a drying method including rotary spraying, nozzle spraying, ultrasonic spraying or a combination thereof.

In the step of heat-treating the composite particles, the heat treatment may be performed at 300 to 1500 ° C.

The method of manufacturing the anode active material may further include a step of coating the composite particles with the amorphous carbon precursor or the low crystalline carbon precursor followed by heat treatment, and the heat treatment may be performed at 300 to 1500 ° C.

The amorphous carbon precursor or the low crystalline carbon precursor may be selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, A styrene resin, a styrene resin, a polyimide resin, an epoxy resin, a vinyl chloride resin, citric acid, stearic acid, polyfluorovinylidene, carboxymethylcellulose (CMC), hydroxypropylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, glucose, gelatin, sugars, coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar, low molecular weight heavy oils or combinations thereof . ≪ / RTI >

Another embodiment of the present invention provides a lithium secondary battery negative electrode including the negative electrode active material.

Another embodiment of the present invention the cathode; anode; And it provides a lithium secondary battery comprising an electrolyte solution.

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

It is possible to realize a lithium secondary battery having improved lifetime characteristics by suppressing the volume change of the negative electrode active material.

FIG. 1A is a schematic view schematically showing one structure of a negative electrode active material according to one embodiment, and FIG. 1B is a schematic diagram illustrating another structure of a negative electrode active material according to an embodiment.
2 is a schematic view showing a rechargeable lithium battery according to one embodiment.
3 is an X-ray diffraction pattern (XRD) graph of the negative electrode active material according to Examples 1 and 2.
4 and 5 are SEM micrographs of the porous silicon compound particles prepared in Example 1 at low magnification and high magnification, respectively.
6 and 7 are SEM micrographs of a negative electrode active material according to Example 1 at a low magnification and a high magnification, respectively.
8 is a scanning electron microscope (SEM) photograph of a section of the negative electrode active material according to Example 2. Fig.
9A and 9B are energy dispersive X-ray analysis (EDS) photographs of the cross section of the negative electrode active material according to Example 2, respectively.
10 and 11 are SEM micrographs of a negative electrode active material according to Example 3 at a low magnification and a high magnification, respectively.
12 is a scanning electron microscope (SEM) photograph of a cross section of a negative electrode active material according to Example 3. Fig.
13A and 13B are energy dispersive X-ray analysis (EDS) photographs of the cross section of the negative electrode active material according to Example 3, respectively.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The anode active material for a lithium secondary battery according to an embodiment may include a porous silicon particle, a core including porous silicon compound particles, and a coating layer surrounding the core. The coating layer may be composed of carbon particles and amorphous carbon or low crystalline carbon which binds the carbon particles.

The structure of the negative electrode active material is specifically shown in Figs. 1A and 1B.

FIG. 1A is a schematic view schematically showing one structure of a negative electrode active material according to one embodiment, and FIG. 1B is a schematic diagram illustrating another structure of a negative electrode active material according to an embodiment.

Referring to FIGS. 1A and 1B, an anode active material 1 according to an embodiment comprises a core 2 and a coating layer surrounding the core 2. The core 2 may be composed of porous silicon particles or porous silicon based compound particles, and the coating layer may be composed of carbon particles 3 and amorphous carbon or low crystalline carbon 4. The amorphous carbon or low crystalline carbon (4) bonds the carbon particles (3) to each other.

FIG. 1A shows a structure in which porous silicon particles or porous silicon compound particles constituting the core 2 are aggregated together. FIG. 1B shows a structure in which porous silicon particles or porous silicon compound particles constituting the core 2 are composed of several particles Shows scattered structure.

The porous silicon based compound particles may be a compound represented by the following formula (1).

[Formula 1]

M _y Si

M in Formula 1 may be at least one element of Groups 1 to 16 elements, specifically, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Ta, W, Re, Os, Mg, Ca, B, P, Al, Ge, Sn, Sb, Bi, Li, O or combinations thereof Among them, preferably Ti, Mn, Fe, Co, Ni, Cu or a combination thereof, which corresponds to the transition metal, and may be the best of these.

The y in the formula (1) may be 0.001 to 0.4, and may be 0.001 to 0.3. When y is within the above range, the porous silicon-based compound particles are excellent in electrical conductivity and have a porosity in a suitable range. Therefore, when used as an anode active material, lithium storage capacity per unit volume of the anode active material is high and cycle life characteristics are excellent.

The core made of the porous silicon particles or the porous silicon-based compound particles may have an average pore size of 2 nm to 3 μm, and specifically an average pore size of 2 nm to 1 μm. The core may also have a porosity of 2 to 90 vol%, specifically 40 to 80 vol%. When the core has the average pore size and porosity within the above range, it plays a buffer against the volume expansion of the core at the time of charge / discharge of the battery, and improves the structural stability of the porous structure, The density can be improved.

The core made of the porous silicon particles or the porous silicon-based compound particles may have an average particle size of 0.3 to 30 mu m, and more specifically, an average particle size of 0.5 to 20 mu m. When the core has an average particle diameter within the above range, an electrode having a high electrode density can be produced.

The carbon particles constituting the coating layer may have an average particle size of 0.1 to 20 mu m, and more specifically, an average particle size of 0.5 to 10 mu m. When the carbon particles have an average particle size within the above range, the carbon particles can uniformly form a coating layer around the core particles, thereby suppressing the volume expansion of the porous silicon in the charging / discharging process.

The carbon particles may be crystalline graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, Ketjen black, super P, graphene, fibrous carbon or a combination thereof.

The crystalline natural graphite can be obtained by separating or pulverizing the ground graphite.

The fibrous carbon may be polyacrylonitrile-based carbon fiber, rayon-based carbon fiber, pitch-based carbon fiber, carbon nanotube, vapor-grown carbon fiber (VGCF) or a combination thereof.

The carbon particles may have an amorphous shape, a flake shape, a plate shape, a spherical shape, a fiber shape, or a mixture thereof.

The ratio of the average particle size size of the carbon particles to the average particle size of the core may be 0.001 to 0.7, and may be 0.002 to 0.5. When the core and the carbon particles have an average particle size ratio within the above range, a uniform coating layer can be formed, and irreversible capacity loss can be prevented during charging and discharging of the battery.

The amorphous carbon or the low crystalline carbon constituting the coating layer may be at least one selected from the group consisting of sucrose, a phenol resin, a naphthalene resin, a polyvinyl alcohol, a furfuryl alcohol resin, a polyacrylonitrile resin, a polyamide resin, (Meth) acrylic resin, polyvinylpyrrolidone, tetra (meth) acrylic acid, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, (EPDM), sulfonated EPDM, starch, glucose, gelatin, saccharides, coal-based pitch, petroleum pitch, polyvinyl chloride, mesophase pitch, tar, low-molecular-weight polyethylene, polypropylene, ethylene-propylene-diene monomer Lt; RTI ID = 0.0 > a < / RTI > heavy oil or a combination thereof.

The amorphous carbon or low-crystalline carbon may be contained in an amount of 0.1 to 90 parts by weight, and specifically 1 to 80 parts by weight, based on 100 parts by weight of the carbon particles. When the amorphous carbon or the low crystalline carbon is contained within the above range, the carbon particles can be sufficiently bonded at the time of forming the coating layer, the buffer can be effectively buffered against the volume expansion of the core, Can be prepared.

The average thickness of the coating layer may be 0.1 to 30 탆, and may be 0.5 to 20 탆. When the average thickness of the coating layer is within the above range, the core may play a buffer against the volume expansion of the core during charging and discharging of the battery, and the core may restrict the reaction with lithium.

The negative electrode active material having the above structure can be produced by the following method.

The negative electrode active material may include a first step of preparing porous silicon particles or porous silicon based compound particles; A second step of coating the surfaces of the porous silicon particles or the porous silicon compound particles with an amorphous carbon precursor or a low-crystalline carbon precursor and carbon particles to produce composite particles; And a third step of heat-treating the composite particles.

The porous silicon based compound particles may be the compound particles represented by Formula 1 as described above.

Firstly, a method for manufacturing the porous silicon particles or the porous silicon-based compound particles, which is the first step, will be described.

The porous silicon particles or the porous silicon-based compound particles may be prepared by etching a silicon-based alloy represented by Formula 2 below.

[Formula 2]

M ' _x Si

M ′ in Formula 2 may be at least one element of Group 1 to Group 16 elements, specifically, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr , Nb, Mo, Ru, Rh, Pd, La, Hf, Ta, W, Re, Os, Mg, Ca, B, P, Al, Ge, Sn, Sb, Bi, Li, O or any combination thereof And among these may preferably include Ti, Mn, Fe, Co, Ni, Cu, C or a combination thereof, and best of these may be Ti.

In Formula 2, x may be 0.01 to 1.0, and may be 0.01 to 0.5. When x is within the above range, the porous silicon particles or the porous silicon-based compound particles are excellent in electrical conductivity and have a porosity in a suitable range. Therefore, when the porous silicon particles or the porous silicon-based compound particles are used as an anode active material, the lithium storage capacity per unit volume of the anode active material is large.

The silicon-based alloy represented by Formula 2 may be prepared as follows.

The silicon-based alloy may be prepared by mixing raw materials containing Si and M '-containing compounds with each other and then mixing the resultant with an atomization method, a rotating electrode method, a melt-spinning method, a mechanical grinding method, Or by mechanical alloying. At this time, the shape, size and microstructure of the silicon-based alloy can be appropriately adjusted by those skilled in the art.

The silicon-based alloy produced may be in powder form.

The silicon-based alloy prepared before the etching, that is, the silicon-based alloy produced before the etching, is composed of the Si phase, the Si and the M '-containing compound phase, and the M' phase, and the Si and M ' . ≪ / RTI > The content ratio of the phases is determined by the type of M ' And the composition ratio of Si. At this time, the Si phase may include at least one element among the elements corresponding to M '.

Accordingly, since the content ratio of the Si phase and the Si and M '-containing compound can be adjusted, the porous silicon particles or the porous silicon-based compound particles having various pore sizes and porosity can be produced.

Then, the porous silicon particles or the porous silicon-based compound particles represented by Formula 1 may be prepared by etching the silicon-based alloy.

The etching is to etch at least one of the Si and M '-containing compound phases and the M' phase in the internal phase of the silicon-based alloy represented by Formula 2 above.

The etching is performed by a chemical method, and an acid solution including hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, acetic acid, phosphoric acid, or a combination thereof may be used. A diluted solution may be used by adding water and alcohol to the acid solution.

Depending on the type of the acid solution, at least one of the Si and M '-containing compound phase and the M' phase can be selectively etched.

After the etching, the obtained porous silicon particles or the porous silicon based compound particles can be washed with water and alcohol.

The chemical method of the etching is not limited thereto and is known to those skilled in the art.

In the production of the porous silicon particles or the porous silicon-based compound particles, a step of heat treatment may be further performed before the etching step.

The heat treatment may be performed in an inert atmosphere such as Ar and a vacuum atmosphere at a temperature of 200 to 1000 ° C, specifically 400 to 800 ° C for 5 minutes to 2 hours. When the heat treatment is performed within the temperature range, the crystallinity of the Si phase, Si and M '-containing compound phase and M' phase existing in the silicon-based alloy is improved and the crystal phases can be uniformly distributed.

In the second step, the surfaces of the porous silicon particles or porous silicon compound particles formed as described above may be coated with an amorphous carbon precursor or a low-crystalline carbon precursor and carbon particles to produce composite particles.

Specifically, the composite particles may be prepared by mixing the porous silicon particles or the porous silicon compound particles, the carbon particles, and the amorphous carbon precursor or the low-crystalline carbon precursor to prepare a mixture, and then performing a coating process.

The carbon particles are as described above.

The amorphous carbon precursor or the low crystalline carbon precursor may be selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, A styrene resin, a styrene resin, a polyimide resin, an epoxy resin, a vinyl chloride resin, citric acid, stearic acid, polyfluorovinylidene, carboxymethylcellulose (CMC), hydroxypropylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, glucose, gelatin, sugars, coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar, low molecular weight heavy oils or combinations thereof Can be used.

The coating process may be performed by a conventional method, and may be performed by a mechanochemical method using a high mechanical energy of milling, a spray drying method, a fluidized bed coating method, a precipitation method, a sputtering method, or the like. Among them, the spray-drying method can be carried out to produce a composite particle having a simple process and a uniform size and shape.

The spray drying may be carried out by a drying method comprising rotary spraying, nozzle spraying, ultrasonic spraying or a combination thereof.

The spray drying may be carried out at a temperature of 50 to 300 캜, specifically at a temperature of 80 to 200 캜. When spray drying is performed in the above-mentioned temperature range, the drying of the solvent is stably performed, so that the structure and shape of the composite particles can be easily controlled.

In the following third step, the prepared composite particles may be heat-treated to produce an anode active material.

At this time, the heat treatment may be performed at 300 to 1500 ° C, specifically 400 to 1200 ° C, in an inert atmosphere such as Ar and a vacuum atmosphere. When the heat treatment is performed in the temperature range, there is less fear that a compound such as silicon carbide will react with the carbon particles constituting the core and the coating layer, thereby reducing the reversible capacity of the amorphous carbon precursor or the low crystalline Carbonization of the carbon precursor may sufficiently occur.

The negative electrode active material may be prepared by coating the prepared composite particles with the amorphous carbon precursor or the low-crystalline carbon precursor followed by heat treatment. At this time, the heat treatment can be performed in the same manner as the heat treatment condition immediately before.

Another embodiment provides a negative electrode for a lithium secondary battery including the negative electrode active material, and another embodiment provides a lithium secondary battery including the negative electrode.

The lithium secondary battery can be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of a separator and an electrolyte to be used. The lithium secondary battery can be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

For example, a cylindrical lithium secondary battery will be described with reference to FIG. And the lithium secondary battery according to one embodiment is not limited thereto.

2 is a schematic view showing a rechargeable lithium battery according to one embodiment.

2, a lithium secondary battery 100 according to an embodiment includes a cathode 114, a cathode 112 opposed to the anode 114, a separator 112 disposed between the anode 114 and the cathode 112, (Not shown) for impregnating the positive electrode 114, the negative electrode 112 and the separator 113, and a battery cell 120 containing the battery cell, And a sealing member 140 sealing the sealing member 120.

The cathode 112 includes the above-described anode active material.

The cathode 112 may be manufactured by mixing the anode active material, the binder and optionally a conductive material to prepare a composition for forming the anode active material layer, and then applying the composition to a cathode current collector such as copper.

The binder may be polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinylchloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or Polypropylene may be used, but is not limited thereto.

As the conductive material, a carbon material, a metal, or the like may be used, and at least one conductive material such as a polyphenylene derivative may be used in combination.

Examples of the carbon material include crystalline graphite such as natural graphite and artificial graphite, amorphous carbon, soft carbon, carbon black, acetylene black, ketjen black and carbon fiber. The metal may be copper, nickel, aluminum, or silver, and may be used in the form of powder or fiber.

The anode active material and the conductive material may be mixed in a weight ratio of 99: 1 to 20:80, and more specifically, in a weight ratio of 98: 2 to 30:70. When mixed in the above-mentioned ratio range, the electrical conductivity is excellent and the capacity of the lithium secondary battery is increased.

The positive electrode 114 includes a positive electrode active material, and the positive active material may be a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound). Specifically, at least one selected from cobalt, manganese, nickel and at least one of a composite oxide of lithium can be used.

The positive electrode 114 may also be prepared by preparing a composition for forming a positive electrode active material layer by mixing the positive electrode active material, a binder and optionally a conductive material in the same manner as the negative electrode 112 and then applying the composition to a positive electrode current collector such as aluminum can do.

As the electrolyte to be charged into the lithium secondary battery 100, a non-aqueous electrolyte or a known solid electrolyte may be used.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based or ketone-based solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) (EC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate may be used.

The separator 113 may be a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / Polypropylene three-layer separator, or the like can be used.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

(Cathode active material production)

Example  One

The raw material of Si and TiH _{1 .9 1:} After mixing the weighed in an atomic ratio of 0.32, the mechanical alloy speech, in particular, to high-energy player using the four planetary mill in an Ar atmosphere was alloyed by milling for 2 hours. The composition of the prepared silicon-based alloy powder was Ti _0.32 Si (Ti ₂₄ Si ₇₆ ).

0.5 g of the silicon-based alloy powder was etched for 30 minutes by using 100 ml of a 1M-concentration hydrofluoric acid solution to prepare a porous silicon-based compound particle powder Ti _0.03 Si (Ti ₃ Si ₉₇ ) having an average particle diameter of 8 μm.

The porous silicon based compound particle powders, toothed graphite having an average particle diameter of 1.7 μm, and coal pitch were mixed at a weight ratio of 28:42:30 by a wet method, and after drying, the mixture was put into a blade type rotor mill, To prepare composite particles.

The composite particles were heat-treated at a temperature of 1000 캜 under an argon atmosphere to prepare an anode active material.

Example  2

The raw material of Si and TiH _{1 .9 1:} After mixing the weighed in an atomic ratio of 0.32, the mechanical alloy speech, in particular, to high-energy player using the four planetary mill in an Ar atmosphere was alloyed by milling for 2 hours. The composition of the prepared silicon-based alloy powder was Ti _0.32 Si (Ti ₂₄ Si ₇₆ ).

The silicon-based alloy powder was heat-treated in an Ar atmosphere at 800 占 폚 for 1 hour and then 0.5g of the silicon-based alloy powder was etched for 30 minutes using 100ml of a 1M solution of a hydrofluoric acid solution to obtain a porous silicon- a _{0 .03 Si (Ti 3 Si 97} ) was prepared.

The porous silicon based compound particle powders, toothed graphite having an average particle diameter of 1.7 탆 and coal pitch were mixed at a weight ratio of 35:35:30 by a wet method, and after drying, the mixture was put into a blade type rotor mill, To prepare composite particles.

The composite particles were heat-treated at a temperature of 1000 캜 under an argon atmosphere to prepare an anode active material.

Example  3

The porous silicon based compound particle powder prepared in Example 1 and the ground graphite having an average particle diameter of 1.7 탆 were mixed with polyvinyl alcohol at a weight ratio of 40:60 in water and stirred to prepare a suspension. Respectively. The obtained powder was heat-treated at 1000 ° C for 1 hour at a temperature raising rate of 5 ° C / min in an argon atmosphere, then added to a tetrahydrofuran solution in which the petroleum pitch was dissolved, and then heat-treated at 1000 ° C in an Ar atmosphere, To prepare an active material.

Comparative example  One

An anode active material was prepared in the same manner as in Example 1, except that silicon powder having an average particle diameter of 8 탆 was used in place of the porous silicon-based compound particle powder used in Example 1.

Comparative example  2

A negative electrode active material was prepared in the same manner as in Example 2, except that silicon powder having an average particle diameter of 8 탆 was used in place of the porous silicon-based compound particle powder used in Example 2.

Comparative example  3

A negative electrode active material was prepared in the same manner as in Example 3, except that silicon powder having an average particle diameter of 8 탆 was used in place of the porous silicon-based compound particle powder used in Example 3.

Evaluation 1: Particle Characterization of the Anode Active Material

The characteristics of the particles constituting the negative electrode active material prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated, and the results are shown in Table 1 below.

The porosity of the core was measured using mercury porosimetry, and the average particle size of the core was measured using a particle size analyzer (PSA).

core Average thickness of coating layer (탆) Average pore size (nm) Porosity (% by volume) Average particle size (占 퐉) Example 1 4 57 8 1.1 Example 2 253 57 8 1.0 Example 3 4 57 8 1.5 Comparative Example 1 X X 8 2.2 Comparative Example 2 X X 8 2.1 Comparative Example 3 X X 8 1.7

X: Pore measurement is not possible.

Evaluation 2: X-ray diffraction  pattern( XRD ) analysis

3 is an X-ray diffraction pattern (XRD) graph of the negative electrode active material according to Examples 1 and 2.

3, it can be seen that, in Examples 1 and 2, graphite phase diffraction peaks due to the porous Si-based compound particles and the graphite phase due to the earth graphite appear. In Examples 1 and 2, Si phase and graphite The intensity ratio of the peak on the surface is different.

Evaluation 3: Scanning electron microscope ( SEM Photo analysis

4 and 5 are SEM micrographs of the porous silicon compound particles prepared in Example 1 at low magnification and high magnification, respectively.

Referring to FIGS. 4 and 5, it can be seen that, in the case of Example 1, silicone-based compound particles having porosity are formed.

6 and 7 are SEM micrographs of a negative electrode active material according to Example 1 at a low magnification and a high magnification, respectively.

6 and 7, it can be seen that the anode active material having the structure in which the core is surrounded by the coating layer is formed in the case of the first embodiment.

8 is a scanning electron microscope (SEM) photograph of a section of the negative electrode active material according to Example 2. Fig.

Referring to FIG. 8, in Example 2, it is confirmed that a negative electrode active material having a structure in which a core is surrounded by a coating layer is formed, and silicone-based compound particles having porosity are present in the core.

9A and 9B are energy dispersive X-ray analysis (EDS) photographs of the cross section of the negative electrode active material according to Example 2, respectively.

Referring to FIGS. 9A and 9B, it can be confirmed that carbon and silicon exist in the anode active material prepared in Example 2.

10 and 11 are SEM micrographs of a negative electrode active material according to Example 3 at a low magnification and a high magnification, respectively.

10 and 11, it can be seen that the anode active material having a structure in which the core is surrounded by the coating layer is formed in the case of Example 3.

12 is a scanning electron microscope (SEM) photograph of a cross section of a negative electrode active material according to Example 3. Fig.

Referring to FIG. 12, in Example 3, it is confirmed that a negative electrode active material having a structure in which a core is surrounded by a coating layer is formed, and silicon-based compound particles having porosity are present in the core.

13A and 13B are energy dispersive X-ray analysis (EDS) photographs of the cross section of the negative electrode active material according to Example 3, respectively.

13A and 13B, it can be confirmed that carbon and silicon are present in the negative electrode active material prepared in Example 3.

(Production of lithium secondary battery)

Each of the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was mixed with carbon black and CMC / SBR (carboxymethylcellulose / styrene-butadiene rubber) in distilled water at a weight ratio of 85: 5: Slurry. The negative electrode slurry was coated on a 10 μm thick copper foil with a doctor blade, dried at 180 ° C. for at least 12 hours, and pressed to prepare a negative electrode plate having a thickness of 45 μm. .

A separator made of a porous polypropylene film was inserted between the working electrode and the counter electrode with the negative electrode serving as the working electrode and the metal lithium foil serving as the counter electrode and a mixed solvent of diethyl carbonate (DEC) and ethylene carbonate (EC) DEC: EC = 1: 1) so that the concentration of LiPF ₆ was 1 mol / L, a 2016 coin type half cell was fabricated.

Evaluation 4: Life characteristic evaluation of lithium secondary battery

The life characteristics of the lithium secondary batteries fabricated according to Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated in the following manner, and the results are shown in Table 2 below.

For one and two cycles, charging was done in CC / CV mode, the termination voltage was maintained at 0.02V, and charging was terminated when the current was 0.02 mA. The discharge was done in CC mode and the termination voltage was maintained at 1.5V. Charging was performed in CC mode from three cycles thereafter, and the final voltage was maintained at 0.02V. The discharge was done in CC mode and the termination voltage was maintained at 1.5V.

In Table 2, the initial efficiency (%) can be obtained by the ratio of the charging capacity and the discharging capacity in one cycle. In Table 2, the reversible capacity retention rate (%) is the percentage value of the reversible capacity at the third cycle with respect to the reversible capacity at the 40th cycle.

Initial Efficiency (%) Reversible capacity at 3 cycles (mAh / g) Reversible Capacity Retention Rate (%) Example 1 89.8 842 98 Example 2 89.5 1061 96 Example 3 88.7 837 98 Comparative Example 1 68.7 521 22 Comparative Example 2 66.4 508 18 Comparative Example 3 63.8 528 21

In Examples 1 to 3 using the negative electrode active material having a structure in which the core composed of the porous silicon particles or the porous silicon based compound particles was surrounded by the coating layer composed of the carbon particles and the amorphous carbon or the low crystalline carbon through Table 2, It can be seen that the initial efficiency and the reversibility capacity retention ratio are higher than those of Comparative Examples 1 to 3 made of silicon.

The present invention is not limited to the above embodiments, but may be manufactured in various forms, and a person skilled in the art to which the present invention pertains has another specific form without changing the technical spirit or essential features of the present invention. It will be appreciated that the present invention may be practiced as. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

1: anode active material
2: core
3: carbon particles
4: amorphous carbon or low-crystalline carbon
100: Lithium secondary battery
112: cathode
113: Separator
114: anode
120: Battery container
140: sealing member

Claims (32)

A core comprising porous silicon particles or porous silicon based compound particles; And
And a coating layer surrounding the core,
The coating layer
Carbon particles; And
And an amorphous carbon or a low-crystalline carbon bonding the carbon particles
Negative electrode active material for lithium secondary battery.
The method of claim 1,
Wherein the porous silicon based compound particles are represented by the following formula (1).
[Formula 1]
M _y Si
(In the formula (1), M includes at least one element of the elements of Groups 1 to 16, and y is 0.001 to 0.4.)
The method of claim 2,
M in Formula 1 is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, La, Hf, Ta, W, Re , Os, Mg, Ca, B, P, Al, Ge, Sn, Sb, Bi, Li, O or a combination thereof, a negative electrode active material for a lithium secondary battery.
The method of claim 1,
Wherein the porous silicon particles or the porous silicon-based compound particles are obtained by etching a silicon-based alloy represented by Formula 2 below.
(2)
M ' _x Si
Wherein M 'comprises at least one element selected from the group consisting of elements of Groups 1 to 16, and x is 0.01 to 1.0.
5. The method of claim 4,
The negative electrode active material for a lithium secondary battery according to claim 2, wherein the silicon-based alloy contains Si, Si and M ', and M'.
The method of claim 1,
Wherein the core has an average pore size of 2 nm to 3 占 퐉 and a porosity of 2 to 90 vol%.
The method of claim 1,
Wherein the core has an average particle size of 0.3 to 30 占 퐉.
The method of claim 1,
Wherein the carbon particles have an average particle size of 0.1 to 20 占 퐉.
The method of claim 1,
Wherein the carbon particles are selected from the group consisting of crystalline quartz graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, Ketjenblack, super P, graphene, fibrous carbon, Anode active material for batteries.
10. The method of claim 9,
The crystalline natural graphite is obtained by separating or pulverizing the ground graphite, and a negative electrode active material for a lithium secondary battery.
10. The method of claim 9,
The fibrous carbon includes a polyacrylonitrile-based carbon fiber, a rayon-based carbon fiber, a pitch-based carbon fiber, a carbon nanotube, a vapor grown carbon fiber (VGCF), or a combination thereof.
The method of claim 1,
The carbon particles may be in the form of amorphous, flaky, plate, spherical, fibrous, or mixed type thereof.
The method of claim 1,
The amorphous carbon or the low crystalline carbon may be at least one selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, A styrene resin, a styrene resin, a polyimide resin, an epoxy resin, a vinyl chloride resin, citric acid, stearic acid, polyfluorovinylidene, carboxymethylcellulose (CMC), hydroxypropylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, glucose, gelatin, sugars, coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar, low molecular weight heavy oils or combinations thereof Wherein the negative electrode active material is carbonized from a precursor containing the negative electrode active material.
The method of claim 1,
Wherein the ratio of the average particle size of the carbon particles to the average particle size of the core is 0.001 to 0.7.
The method of claim 1,
Wherein the average thickness of the coating layer is 0.1 to 30 탆.
The method of claim 1,
Wherein the amorphous carbon or low crystalline carbon is contained in an amount of 0.1 to 90 parts by weight based on 100 parts by weight of the carbon particles.
The method of claim 1,
Wherein the amorphous carbon or the low-crystalline carbon further surrounds the coating layer.
Preparing porous silicon particles or porous silicon-based compound particles;
Coating the surfaces of the porous silicon particles or the porous silicon-based compound particles with an amorphous carbon precursor or a low-crystalline carbon precursor and carbon particles to produce composite particles; And
Heat treating the composite particles
Method for producing a negative electrode active material for a lithium secondary battery comprising a.
19. The method of claim 18,
Wherein the porous silicon-based compound particles are represented by Formula 1 below.
[Formula 1]
M _y Si
(In the formula (1), M includes at least one element of the elements of Groups 1 to 16, and y is 0.001 to 0.4.)
20. The method of claim 19,
The step of preparing the porous silicon particles or the porous silicon based compound particles includes a step of etching a silicon-based alloy represented by the following formula (2).
(2)
M ' _x Si
Wherein M 'comprises at least one element selected from the group consisting of elements of Groups 1 to 16, and x is 0.01 to 1.0.
21. The method of claim 20,
The method for producing a negative active material for a lithium secondary battery according to claim 1, wherein the silicon-based alloy represented by the formula (2) comprises an Si phase, Si and a M '-containing compound phase, and M' phase.
The method of claim 21,
Wherein the porous silicon particles or the porous silicon based compound particles are produced by etching at least one of the Si and M 'containing compound phase and the M' phase.
21. The method of claim 20,
Wherein the step of preparing the porous silicon particles or the porous silicon based compound particles further comprises a step of heat treating the porous silicon particles or the porous silicon based compound particles before the etching step.
24. The method of claim 23,
Wherein the heat treatment is performed at a temperature of 200 to 1000 ° C.
19. The method of claim 18,
Wherein the step of preparing the composite particles comprises:
Mixing the porous silicon particles or the porous silicon-based compound particles, carbon particles, and an amorphous carbon precursor or a low-crystalline carbon precursor to produce a mixture; And
Performing the coating process including the mechanochemical method, the spray drying method, the fluidized bed coating method, the precipitation method, or the sputtering method using the mixture
Method for producing a negative electrode active material for a lithium secondary battery comprising a.
26. The method of claim 25,
Wherein the spray drying method is performed by a drying method including rotary spraying, nozzle spraying, ultrasonic spraying, or a combination thereof.
19. The method of claim 18,
Wherein the heat treatment is performed at 300 to 1500 占 폚.
19. The method of claim 18,
And coating the composite particle with the amorphous carbon precursor or the low-crystalline carbon precursor, followed by heat treatment
A method for producing a negative electrode active material for lithium secondary batteries.
29. The method of claim 28,
Wherein the heat treatment is performed at 300 to 1500 占 폚.
19. The method of claim 18,
The amorphous carbon precursor or the low crystalline carbon precursor may be selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, A styrene resin, a styrene resin, a polyimide resin, an epoxy resin, a vinyl chloride resin, citric acid, stearic acid, polyfluorovinylidene, carboxymethylcellulose (CMC), hydroxypropylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, glucose, gelatin, sugars, coal based pitches, petroleum pitches, polyvinyl chloride, mesophase pitches, tar, low molecular weight heavy oils or combinations thereof And a negative electrode active material for lithium secondary batteries.
18. The negative active material of any one of claims 1 to 17.
And a negative electrode for a lithium secondary battery.
31. A cathode according to claim 31,
anode; And
Electrolyte
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