KR20140070162A - Anode active material for lithium secondary battery with high capacity, a manufacturing method of the same and Lithium secondary battery comprising the same - Google Patents

Abstract

An anode active material for a lithium secondary battery comprises: a core unit which is a mixed composite including a first particulate matter made of a metal (metalloid) capable of alloying with lithium, and a second particulate matter made of an oxide of a metal (metalloid) identical to or different from the metal (metalloid) of the first particulate matter; and a conductive carbon layer coated on at least partial exterior of the core unit. One first particulate matter or an assembly of more than two first particulate matters is surrounded by the second particulate matter, and the mole ratio of the metal (metalloid) oxide to the mole ratio of the metal (metalloid) in the mixed composite is adjusted to exceed 0 and to be less than 1, and the second particulate matter has an amorphous structure. The secondary battery according to the present invention has a high capacity; minimizes a dead volume on the anode as an irreversible matter such as lithium oxide or lithium metal oxide is less produced in the initial charge or discharge of the battery; has an excellent cycleability by minimizing the volume expansion during charge or discharge; and improves the electric conductivity due to the conductive coating on the surface so as to have an excellent rate control property, by using the anode active material for a lithium secondary battery of the present invention.

Description

[0001] The present invention relates to a high-capacity anode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the anode active material,

The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery using the same.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. The electrochemical device is one of the most remarkable fields in this respect, and development of a rechargeable secondary battery has become a focus of attention. In recent years, research and development on the design of new electrodes and batteries have been proceeding in order to improve capacity density and specific energy in developing such batteries.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and much higher energy density than conventional batteries such as N-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution .

Generally, a lithium secondary battery is manufactured by using a material capable of intercalation and disintercalation of lithium ions as a cathode and an anode, filling an organic electrolytic solution or a polymer electrolyte between a cathode and an anode, And generate electrical energy by an oxidation reaction and a reduction reaction when they are inserted and desorbed.

At present, a carbonaceous material is mainly used as an anode active material constituting a cathode of a lithium secondary battery. In the case of graphite, the theoretical capacity is about 372 mAh / g, and the actual capacity of graphite commercialized at present is about 350 to 360 mAh / g. However, such a capacity of a carbonaceous material such as graphite is not compatible with a lithium secondary battery which requires a high capacity of a negative electrode active material.

In order to satisfy such a demand, there is an example of using Si, Sn, or the like, which is a metal capable of electrochemically alloying with lithium and exhibiting a higher charge / discharge capacity than a carbonaceous material, as a negative electrode active material. However, such a metal-based negative electrode active material has a large volume change accompanied by the charge / discharge of lithium and cracks and becomes undifferentiated. Therefore, the capacity of the secondary battery using such a metal-based negative active material decreases sharply as the charge- There may be a problem of this being shortened.

In order to solve the problem caused by the use of the metal-based anode active material by using a metal oxide such as Si, Sn or the like as the anode active material, lithium oxide or lithium metal oxide, which is an irreversible phase during the initial reaction with lithium, There is a problem that the initial efficiency is lower than that of the active material and low electrical conductivity.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the above-mentioned problems and to provide a negative electrode active material which has a higher capacity than the carbonaceous anode active material, minimizes volume expansion during charge and discharge, has a relatively high initial efficiency, The present invention also provides a negative electrode active material for a lithium secondary battery and a method for producing the negative electrode active material.

In order to solve the above problems, an aspect of the present invention is to provide a lithium secondary battery comprising a first particulate phase made of a (alloying) metal capable of being alloyed with lithium and a second particulate phase made of an oxide of a (same or different) A core part which is a mixed composite comprising And a conductive carbon layer coated on the outside of at least a portion of the core portion, wherein the one first particulate or at least two first particulate aggregates are surrounded by a second particulate particulate, Wherein the molar ratio of the (sub) metal oxide to the metal (moles of the (sub) metal oxide / mole of the (sub) metal) is controlled to be more than 0 and less than 1, and the second particulate phase is an amorphous structure. do.

According to one embodiment of the present invention, the core portion may be a composition represented by the following Chemical Formula 1 or Chemical Formula 2.

In the above Formulas 1 and 2, M, M ¹ and M ² are independently selected from the group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga and alloys thereof.

According to an embodiment of the present invention, the molar ratio of the (sub) metal to the (sub) metal oxide may be in the range of more than 80:20 but less than 50:50

According to an embodiment of the present invention, there may be a negative active material for a lithium secondary battery having no (sub) metallic crystal on the second particle.

According to an embodiment of the present invention, the conductive carbon may be amorphous, crystalline, or a mixture thereof. The content of the conductive carbon may be 1 to 20 parts by weight based on 100 parts by weight of the core, The thickness of the carbon layer may be between 5 and 1000 nm.

According to another aspect of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: mixing oxide particles capable of being alloyed with lithium and oxide particles of the same or different (sub-) metal as the (sub) Wherein the mixture is mechanically alloyed so that a first particulate or a first particulate aggregate is surrounded by a second particulate phase and the molar ratio of the (sub) metal oxide to the molar ratio of the (sub) Is less than 1 and less than 1; And coating the surface of the core with conductive carbon, wherein the second particulate phase is an amorphous structure. The present invention also provides a method of manufacturing a negative active material for a lithium secondary battery.

According to one embodiment of the present invention, the mixing and mechanical alloying treatment may be performed under an oxygen-shielded condition, and the oxygen-shielded condition may be an inert gas condition in which nitrogen, argon, helium, krypton or xenon gas is present; Hydrogen gas conditions; Or vacuum conditions.

According to an embodiment of the present invention, the coating of the conductive carbon may be performed by mixing the core material and the liquid or gaseous conductive carbon precursor, and performing the heat treatment. Alternatively, the coating may be performed by mechanical alloying of the core material and the conductive carbon particles .

According to another aspect of the present invention, there is provided a lithium secondary battery electrode comprising an electrode current collector and a negative electrode active material layer including at least one surface of the electrode current collector, wherein the negative electrode active material is a negative electrode active material according to the present invention The electrode for a lithium secondary battery is provided.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the negative electrode is the negative electrode according to the present invention.

The lithium secondary battery using the negative electrode active material of the present invention not only has a high capacity but also generates a less irreversible phase such as lithium oxide or lithium metal oxide during initial charging and discharging of the battery, minimizing the dead volume on the anode side, The cycle characteristics are minimized and the conductivity of the surface is improved due to the conductive coating on the surface, so that it is possible to have an excellent rate-limiting characteristic.

Hereinafter, embodiments of the present invention will be described in detail to facilitate understanding of the present invention. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following embodiments. Embodiments of the invention are provided to more fully describe the present invention to those skilled in the art.

The present invention relates to a composite part comprising a mixed particle comprising a first particulate phase made of a (sub) metal which can be alloyed with lithium and a second particulate phase made of an oxide of the same or different (sub) metal as the (sub) And a conductive carbon layer coated on the outside of at least a portion of the core portion, wherein the one first particulate or at least two first particulate aggregates are surrounded by a second particulate particulate, Wherein the molar ratio of the (sub) metal oxide to the metal (moles of the (sub) metal oxide / mole of the (sub) metal) is controlled to be greater than 0 and less than 1, and the second particulate phase is an amorphous structure.

When lithium (such as silicon) alloyable metal is used as a negative electrode active material, cracks or undifferentiation occurs due to volume change caused by repetitive charging and discharging of the battery, thereby deteriorating the battery and thereby deteriorating the capacity of the battery there was. In addition, when the (quasi-) metal oxide is used as the negative electrode active material, lithium oxide or lithium oxide, which is an irreversible phase due to the initial reaction with lithium ions, is formed to lower the initial efficiency and the problem that the electric conductivity can not reach an appropriate value there was

Therefore, in order to prevent the volume change due to charging and discharging when the (quasi-) metal is used as the negative electrode active material, the present inventors surrounded the (quasi) metal particle phase with the (sub) metal oxide particle phase and simultaneously controlled the second particle phase with the amorphous structure And a conductive carbon layer that minimizes irreversible phase and improves electric conductivity while maintaining the structure, by controlling the (sub) metal oxide molar ratio to the molar ratio of the (sub) metal to the (sub) As a negative electrode active material, at the same time.

Sn, Al, Sb, Bi, As, Ge, Pb (Bi), and the like may be used as long as it is a metal or a metalloid capable of being alloyed with lithium according to an embodiment of the present invention. , Zn, Cd, In, Ti, and Ga. In view of the capacity of the secondary battery, Si is preferable. The (sub) metal oxide forming the second particulate phase is not particularly limited as long as it is an oxide of a metal or a metalloid, which is the same as or different from the metal forming the first particulate phase, and is a metal or metalloid oxide capable of alloying with lithium And may be an oxide of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, or Ga. Silicon oxide is preferable from the viewpoint of the capacity of the secondary battery. The aggregation of the first particulate phase or the second particulate phase is surrounded by the second particulate phase formed by the (quasi) metal oxide, so that the first particulate phase or the second particulate phase can be largely generated due to the reaction of the first particulate phase and lithium during charging / The volume change of the first particulate phase can be minimized.

Also, the first particulate phase surrounded by the second particulate phase prevents volume expansion, and the second particulate phase maintains an amorphous structure in the negative active material and can minimize the volume change of the negative active material.

It is more preferable that the second particulate phase is free of (quasi) metal crystal.

In the present invention, a structure free of (quasi-) metal crystal means that Si crystal or the like does not exist in the silicon oxide when, for example, the (quasi-) metal oxide is silicon oxide. Specifically, the Si crystal means a crystal having a grain size of 5 to 50 nm and a crystal having a grain size larger than that of the crystal.

Therefore, since the volume change of the first particulate phase by the second particulate phase can be minimized and at the same time, the volume change of the negative electrode active material can be minimized or suppressed when the battery is charged and discharged as the amorphous second particulate phase, The secondary battery to be used may have a lower volume change rate than any battery using a metal that can be alloyed with lithium.

The average particle diameter of the first particle and the second particle is not particularly limited, but may be 0.1 to 100 nm.

If the (sub) metals of the first particle and the second particle are the same, the composition of the mixed complex according to the present invention can be represented by the following formula (1).

[Chemical Formula 1]

MO _x (0 < x < 1)

In the above Formulas 1 and 2, M, M ¹ and M ² are independently selected from the group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga and alloys thereof.

In addition, when the (first) particle on the first particle and the (sub) metal on the second particle are different, the composition of the mixed complex of the present invention can be represented by the following formula (2).

(2)

M ¹ _y M ² _z O _x (y + z = 1, 0 <x <1)

In the above Formulas 1 and 2, M, M ¹ and M ² are independently selected from the group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga and alloys thereof.

Such a mixed complex is formed by mixing (sub) metal particles and (sub) metal oxide particles by mechanical alloying treatment, wherein the molar ratio of the (sub) 1, greater than 80:20, less than 50:50, or 70:30 to 55:45. In the above range, it can exhibit an effect as a high capacity anode active material and prevent an increase in the amount of formation of lithium oxide, which is an irreversible phase due to the initial reaction with lithium ions, to prevent a decrease in the initial efficiency of the battery. Further, it is possible to maintain the (quasi-) metal oxide capable of effectively suppressing the volume change of the (sub) metal in the above ratio, thereby preventing the crack and the undifferentiation of the negative electrode active material, thereby preventing the battery capacity and the battery life.

Therefore, when the mixed composite according to the present invention in which the molar ratio of the (quasi) metal oxide to the (quasi) metal molar ratio is adjusted to reduce the oxygen content in the mixed composite is used as the negative active material, the secondary battery comprising the negative active material, It is possible to have a higher initial efficiency than a conventional secondary battery using a possible (quasi-) metal or the (quasi) metal oxide as a negative electrode active material.

Also, the negative electrode active material of the present invention has a conductive carbon layer coated on the outside of at least a part of the core portion. Although the negative electrode active material core part of the present invention increases the initial efficiency, the electrical conductivity is low and the rate-dependency characteristic may not be good at the time of charging and discharging. The rate capability is a characteristic with respect to the rate of charging / discharging. When the charging / discharging rate is excellent, the rate characteristic is excellent. The core portion according to the present invention has a high capacity, but if the speed ratio characteristic is poor in the actual current region used, it may not be possible to use up the capacity of the core portion, resulting in a failure to utilize the advantages of the high capacity portion.

Accordingly, the negative electrode active material of the present invention can increase the electrical conductivity by the conductive carbon coating and thereby improve the speed-rate characteristic, thereby making it possible to sufficiently exhibit the advantage of the high capacity of the core portion due to various characteristics described above.

The conductive carbon forming the coating layer in the present invention is not particularly limited as long as it is a carbon-based material having conductivity. Amorphous or crystalline, and may be formed by carbonizing the conductive carbon precursor or may be formed by directly coating the conductive carbon particles. As the precursor of the conductive carbon, any liquid or gaseous organic compound containing carbon may be used without limitation. For example, the precursor of the conductive carbon includes a liquid precursor such as toluene, pitch, heavy oil, and resin, and a vapor precursor such as methane, ethane, propane, ethylene, acetylene, etc. At this time, A melamine resin, a phenol resin, an epoxy resin, an unsaturated polyester resin, an alkyl resin, an alkyd resin, a urethane resin or the like can be used. However, the thermosetting resin is not limited thereto. .

Examples of the conductive carbon particles include carbon black such as acetylene black, thermal black, furnace black, and channel black, carbon fibers such as carbon black, A carbon tube, a graphene, and the like, but the present invention is not limited thereto.

The content of the conductive carbon can be variously adopted depending on the coating method or the specific battery type in which the active material is used. For example, it may be 1 to 20 parts by weight based on 100 parts by weight of the core portion, but is not limited thereto. In the case of the above content, the surface can be uniformly coated to secure sufficient conductivity, and the ratio of the core portion can be such a level as to realize a high capacity.

The thickness of the conductive carbon layer can be variously adopted depending on the coating method or the specific battery type in which the active material is used. For example, 5 to 1000 nm, but is not limited thereto.

The present invention also relates to a method for manufacturing a lithium secondary battery, comprising the steps of: mixing oxide particles capable of being alloyed with lithium and oxide particles of the same or different (quasi) metal as the (quasi) metal;

The mixture is subjected to a mechanical alloying treatment so that a first particulate or a second particulate aggregate is surrounded by the second particulate phase and the molar ratio of the (sub) metal oxide to the (sub) (Number of moles of (zirconium) metal oxide / mole of (zirconium) metal) is more than 0 and less than 1; And

And coating the surface of the core with conductive carbon

And the second particulate phase is an amorphous structure.

The mechanical alloys may be performed using a Mechano fusion device known in the art. Examples of the Mecano fusion apparatus include a high energy ball mill apparatus, a planetary mill apparatus, a stirred ball mill apparatus, a vibration mill apparatus, and the like . It is preferable to perform this in a high energy ball mill apparatus.

In order to control the molar ratio of the (sub) metal oxide to the molar ratio of the (sub) metal in the mixed complex produced by the production method of the present invention to be controlled to be greater than 0 and less than 1, It is preferable to perform it under the blocked condition. Inert gas conditions in which, for example, nitrogen, argon, helium, krypton or xenon gas are present; Hydrogen gas conditions; Or vacuum conditions.

At this time, the average particle diameter of the (sub) metal and the (sub) metal oxide is not particularly limited, but may be in the range of 0.05 to 50 탆. In order to shorten the mixing time and mechanical alloying time, Do.

Next, conductive carbon is coated on the surface of the core portion.

The coating of the conductive carbon may be carried out by mixing the core material and the liquid or gaseous conductive carbon precursor and heat treatment, or may be performed by mechanical alloying treatment of the core material and the conductive carbon particles.

When a carbon precursor is used, the carbon precursor is brought into contact with the surface of the core material and then heat-treated to carbonize the carbon precursor to form a conductive carbon coating layer. In order for the conductive carbon coating layer to be uniformly formed outside the core portion, it is preferable that the carbon precursor is uniformly mixed with the core portion material. When a liquid carbon precursor is used, a dispersant may be added. When a gaseous carbon precursor is used, a gaseous carbon precursor is continuously introduced into the core active material, A tubular furnace can be used. The heat treatment temperature of the precursor is preferably 500 to 1200 ° C. It is also preferable that the heat treatment is carried out under inert conditions.

In order to directly coat the conductive carbon particles on the core portion, the above-described mechanical alloying treatment method can be applied. The conductive carbon particles can be attached to the surface of the core portion while mechanical stress is applied simultaneously with the mixing of the core material and the conductive carbon particles.

The electrode active material of the present invention can be produced as an anode or a cathode according to a manufacturing method commonly used in the art. For example, a slurry may be prepared by mixing and stirring a binder and a solvent, and if necessary, a conductive agent and a dispersant in the electrode active material of the present invention, applying the slurry to a collector, and compressing the electrode to produce an electrode.

Examples of the binder include polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride, polyvinylidene fluoride-trichlorethylene polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, But are not limited to, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, ), Cellulose acetate propionate but are not limited to, polyvinylpyrrolidone, opionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose but are not limited to, carboxyl methyl cellulose (CMC), acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidenefluoride, polyacrylonitrile, Butadiene rubber (SBR), or a mixture of two or more thereof. However, it is not limited thereto and various kinds of binder polymers may be used.

When the electrode is manufactured, a lithium secondary battery having a separator and an electrolyte interposed between the positive electrode and the negative electrode, which is conventionally used in the art, can be manufactured using the electrode.

In the electrolyte used in the present invention, the lithium salt that may be included as the electrolyte may be any of those conventionally used in an electrolyte for a lithium secondary battery. For example, examples of the anion of the lithium salt include F ^- , Cl ^- , Br ^{- _{, I -, NO 3 -,}} N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 _{^{PF 2 -, (CF 3)}} 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N _{^{-, CF 3 CF 2 (CF}} 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Examples of the organic solvent included in the electrolytic solution used in the present invention include those conventionally used for an electrolyte for a lithium secondary battery, and examples thereof include fluoro-ethylene carbonate (FEC), methyl propiolate Methyl propionate, ethyl propionate, propyl propionate, buthyl propionate, propylene carbonate, PC, ethylene carbonate (EC) Diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, Vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran And furan, or a mixture of two or more thereof. In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high-viscosity organic solvent and dissociate the lithium salt in the electrolyte well. In this cyclic carbonate, dimethyl carbonate and diethyl When a low viscosity, low dielectric constant linear carbonate such as carbonate is mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

Alternatively, the electrolytic solution stored in accordance with the present invention may further include an additive such as an overcharge inhibitor or the like contained in an ordinary electrolytic solution.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not. Or a separator including a porous organic-inorganic coating layer containing a mixture of inorganic particles and a binder polymer on at least one side of the porous polymer film or the porous nonwoven fabric.

The battery case used in the present invention may be of any type that is commonly used in the art, and is not limited in its external shape depending on the use of the battery. For example, a cylindrical case, a square type, a pouch type, (coin) type or the like.

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

Example

Example  One

< Core portion  Manufacturing>

The average particle diameter of about 3㎛ the silicon powder and the average particle diameter of about 1㎛ the silicon oxide (SiO ₂₎ powder, 70: a mixture of 30 molar ratio to form a powder mixture. This mixture powder and a stearless ball having a diameter of about 5 mm were mechanically alloyed at a weight ratio of 1:15 at a rotation speed of 1000 rpm for 180 minutes using a high energy ball mill to prepare a core part of the mixed composite of the present invention . The mixed composite was prepared under argon gas conditions.

&Lt; Conductive carbon coating >

The core portion 10g was charged into a rotating tubular furnace, and argon gas was flowed at 0.5 L / min. Then, the temperature was raised to 900 DEG C at a rate of 5 DEG C / min. The silicon tubular anode active material having a conductive carbon coating layer formed by rotating the rotating tubular furnace at a rate of 10 rpm / min while flowing argon gas at 1.8 L / min and acetylene gas at 0.3 L / min for 2 hours. The carbon content of the conductive carbon coating layer at this time was 5.3 parts by weight based on 100 parts by weight of the core portion. The thickness of the shell part was observed to be 40 nm from the TEM analysis.

<Manufacture of Battery>

The anode active material and graphite were mixed so as to have a capacity of 540 mAh / g. Then, carbon black and SBR / CMC were mixed as a conductive material in a weight ratio of 94: 2: 2: 2. These were mixed in distilled water as a solvent and mixed to prepare a uniform negative electrode slurry. The negative electrode slurry was coated on one surface of the copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a required size to prepare a negative electrode.

Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70, and LiPF ₆ and FEC 5% were added to the nonaqueous electrolyte solvent to prepare a 1 M LiPF ₆ nonaqueous electrolyte solution.

A coin-type battery was prepared by using the electrode thus prepared according to the present invention as a negative electrode, using a lithium metal foil as a counter electrode, interposing a polyolefin separator between both electrodes, and injecting the electrolyte solution.

Comparative Example  One

A negative electrode active material and a battery were provided in the same manner as in Example 1, except that silicon composite powder was mixed with silicon oxide (SiO ₂ ) powder in a molar ratio of 50:50, followed by vapor deposition.

Comparative Example  2

Except that the electrode active material was prepared so that the Si crystal existed in the negative electrode active material.

Comparative Example  3

The negative electrode active material and the battery were prepared in the same manner as in Example 1, except that the negative electrode active material not coated with the core portion was used.

Experimental Example  1 - Measurement of cell thickness variation

Changes in the thickness of the battery were measured using the cells prepared according to Examples and Comparative Examples. The measurement evaluation is shown in Table 1.

Experimental Example  Two-cell Charging and discharging  characteristic

Charging and discharging characteristics were evaluated using batteries manufactured according to Examples and Comparative Examples.

The battery was charged at a constant current up to 5 mV, and then charged at 5 mV until the current reached 0.005 C and then terminated. The discharge of the battery was performed at a constant current up to 1.0V.

The rate-limiting characteristic evaluation was performed by charging and discharging at 0.1 C before calculating the rate-of-load characteristic, and calculating the charging and discharging rate based on the charging and discharging capacities at that time. In case of the discharge rate, the charging was carried out at 0.1 C and discharged at the rate so as to minimize the influence of the charging rate.

The evaluation results of charge-discharge characteristics are shown in Table 1 below.

Life characteristics (%) Electrode expansion rate
(50 ^th charge)
(%) Powder resistance
(ohm · cm) Discharge capacity
(mAh / g) Initial efficiency
(%) Rate characteristics (%) charge Discharge 0.5 C 1.0 C 2.0C 0.5 C 1.0 C 2.0C Example 1 91.5 44 2.45 * 10 ^-1 539 88.6 99.2 98.5 95.7 97.3 96.8 94.3 Comparative Example 1 91.2 45 3.79 * 10 ^-1 542 83.9 99.5 98.1 96.0 97.9 96.2 94.7 Comparative Example 2 83.4 62 3.28 * 10 ^-1 540 88.5 97.1 95.6 93.3 96.7 94.3 92.9 Comparative Example 3 85.7 54 5.53 * 10 ⁹ 543 87.6 95.5 92.7 84.9 93.2 91.5 83.1

Example 1 and Comparative Example 1 show that the initial efficiency was increased by decreasing the amount of oxygen fed, and the life characteristics and thickness expansion characteristics were also similar. In addition, excellent rate-limiting properties were confirmed by carbon coating.

On the other hand, in the case of Comparative Example 2, the initial capacity and efficiency characteristics were similar to each other as the Si crystal grains were grown, but the lifetime characteristics were lowered and the thickness expansion rate was also increased. The rate-limiting characteristic was not so bad due to the carbon coating, but it was found that the small rate-limiting characteristic was decreased as compared with Example 1 due to the Si crystal grain growth.

In addition, in Comparative Example 3, since the carbon was not coated on the surface, not only the rate-limiting characteristic was greatly reduced but also the lifetime characteristics were deteriorated. Moreover, uniform electron transfer to the Si material was difficult and the thickness expansion was uneven, .

Claims (15)

A core portion that is a mixed composite comprising a first particulate phase of a (sub) metal which can be alloyed with lithium and a second particulate phase of an oxide of the same or different (sub) metal as the (sub) And a conductive carbon layer coated on the outside of at least a part of the core portion,
Wherein the aggregation of the first particulate phase or the second particulate phase is surrounded by the second particulate phase and the molar ratio of the (sub) metal oxide to the (sub) / (Sub) metal) is controlled to be more than 0 and less than 1, and the second particulate phase is an amorphous structure. The method according to claim 1,
Wherein the mixed composite has a composition represented by the following Chemical Formula 1 or Chemical Formula 2:
[Chemical Formula 1]
MO _x (0 < x &lt;1);
(2)
M ¹ _y M ² _z O _x (y + z = 1, 0 <x <1)
In the above Formulas 1 and 2, M, M ¹ and M ² are independently selected from the group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga and alloys thereof. The method according to claim 1,
Wherein the molar ratio of the (sub) metal to the (sub) metal oxide is in the range of more than 80:20 to less than 50:50. The method according to claim 1,
And the second particulate phase is free of (quasi) metallic crystal. The method according to claim 1,
Wherein the (quasi-) metal is silicon and the (quasi-) metal oxide is silicon oxide. The method according to claim 1,
Wherein the conductive carbon is amorphous, crystalline, or a mixture thereof. The method according to claim 1,
Wherein the amount of the conductive carbon is 1 to 20 parts by weight based on 100 parts by weight of the core part. The method according to claim 1,
And the thickness of the conductive carbon layer is 5 to 1000 nm. Mixing the (sub) metal particles capable of alloying with lithium and oxide particles of the same or different (sub) metals as the (sub) metal;
The mixture is subjected to mechanical alloying treatment so that a first particulate or a second particulate aggregate aggregate is surrounded by the second particulate phase and the ratio of the (sub) metal oxide with respect to the molar ratio of the (sub) Preparing a core part which is a mixed composite having a molar ratio of more than 0 and less than 1; And
And coating the surface of the core with conductive carbon
And the second particulate phase is an amorphous structure. 10. The method of claim 9,
Wherein the mixing and mechanical alloying treatment is performed under a condition that oxygen is shut off. 11. The method of claim 10,
The oxygen is shut off under inert gas conditions in the presence of nitrogen, argon, helium, krypton or xenon gas; Hydrogen gas conditions; Or a vacuum condition for a negative electrode active material for a lithium secondary battery. 10. The method of claim 9,
Wherein the coating of the conductive carbon is performed by mixing a core material and a liquid or gaseous conductive carbon precursor, followed by heat treatment. 10. The method of claim 9,
Wherein the coating of the conductive carbon is performed by a mechanical alloying method of the core material and the conductive carbon particles. And a negative electrode active material layer including a negative electrode active material on at least one surface of the electrode current collector,
The electrode for a lithium secondary battery according to any one of claims 1 to 8, wherein the negative electrode active material is a negative electrode active material for a lithium secondary battery. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
And the negative electrode is the negative electrode according to claim 14.