KR20150040105A - Anode active material, lithium secondary battery comprising the material, and method of preparing the material - Google Patents

Abstract

The present invention provides an anode active material which comprises: a core part including (semi)metal oxide-Li alloyed MOx-Liy; and a (MOx-Liy)-C composite of core-shell structure, wherein M is a (semi) metal, x is greater than 0 and less than 1.5, and y is greater than 0 and less than 4, and having a shell part including a carbon material coated on the surface of the core part. Through this, the invention has a high-capacity, excellent control ability for the cycle property and volume expansion, and also can provide the anode active material having a high initial efficiency.

Description

[0001] The present invention relates to a negative electrode active material, a lithium secondary battery including the same, and a method for manufacturing the negative electrode active material,

The present invention relates to a negative electrode active material including a composite of a negative electrode active material, specifically a core-shell structure, a lithium secondary battery including the same, and a method for manufacturing the negative electrode active material.

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. Electrochemical devices have attracted the greatest attention in this respect, among which the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve the capacity density and specific energy in developing such batteries, And research and development on the design of the battery.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution . However, among these lithium ion secondary batteries, there are safety problems such as ignition and explosion in using an organic electrolytic solution, and they are disadvantageous in that they are difficult to manufacture. Recently, the lithium polymer secondary battery is considered to be one of the next generation batteries by improving the weak point of such a lithium ion secondary battery. However, since the capacity of the battery is still relatively low as compared with the lithium ion secondary battery and the discharge capacity at low temperature is insufficient There is an urgent need for improvement.

For this purpose, there is a growing need for a high-capacity anode material, and a (quasi) metallic material such as a Si-based or Sn-based material having a large theoretical capacity is applied as a negative electrode active material. However, as the charging and discharging are repeatedly performed, The characteristics were deteriorated and the volume expansion was severe, which adversely affected the performance and safety of the battery. Therefore, research has been carried out to mitigate cycle characteristics and volume expansion by using (quasi-) metal oxides such as silicon oxides (SiOx), but the (quasi-) metal oxides have been found to be non- So that the initial efficiency is extremely low.

In order to compensate for this, when the (quasi-) metal oxide is pre-alloyed with the (quasi) metal oxide and lithium so as to contain lithium, irreversible phase such as lithium oxide, lithium metal oxide, The initial efficiency of the negative electrode active material can be increased.

However, lithium by-products generated in the course of the reaction between the (quasi-) metal oxide and the lithium source may remain on the surface of the composite, and as a result, the pH of the aqueous binder system including the quasi-metal oxide is increased to make it difficult to mix the slurry of the anode active material. There is a problem that the adhesive force to the electrode is weakened by changing the physical properties of the binder in the slurry.

Accordingly, an object of the present invention is to provide an anode active material having excellent cyclic characteristics and volume expansion control ability between a lithium source and a (quasi-) metal oxide while suppressing reactivity with a by- .

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: forming a core portion including a (sub) metal oxide-Li alloyed (MO _x -L _y ) (MO _x -Li _y ) -C composite wherein M is a (sub) metal, x is more than 0 and less than 1.5, and y Is more than 0 and less than 4).

According to a preferred embodiment of the present invention, the shell portion is a multi-coated shell portion including a primary carbon coating before Li alloying and a secondary carbon coating after Li alloying. Thereby providing a negative electrode active material.

According to an embodiment of the present invention, the shell portion is characterized in that the lithium by-product, including lithium metal powder, lithium silicate compound, lithium carbonate, and a mixture thereof, is not exposed to the surface.

In addition, according to one embodiment of the present invention, the negative electrode active material of the core-shell structure has a pH of 1 to 11 in an aqueous system.

According to an embodiment of the present invention, the carbon material of the secondary carbon coating includes amorphous carbon selected from the group consisting of coal-based pitch, petroleum pitch, tar, low molecular weight heavy oil, and mixtures thereof The secondary carbon coating may be coated by a chemical vapor deposition (CVD) method, and the carbon material of the secondary carbon coating may be 1 to 15 wt% based on the weight of the negative active material.

According to an embodiment of the present invention, the carbon material of the primary carbon coating may be crystalline carbon, amorphous carbon, or a mixture thereof, and the carbon material of the primary carbon coating may be 0.05 to 20 wt. %. ≪ / RTI >

According to an embodiment of the present invention, the (sub) metal may be selected from the group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga, And the (sub) metal oxide may be one kind of compound selected from the group consisting of SiO, SnO and SnO ₂ , or a mixture of the two, and the diameter of the core part may be 0.05 to 30 탆.

According to another aspect of the present invention, there is provided a negative electrode for a lithium secondary battery comprising a current collector and a negative electrode active material layer formed on at least one side of the current collector, the negative active material layer comprising the negative active material according to the present invention.

According to another aspect of the present invention, there is provided a lithium secondary battery including a positive electrode, a negative electrode according to the present invention, and a separator interposed between the positive electrode and the negative electrode.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: (S1) subjecting a surface of a core portion including an oxide of a (sub) metal to a primary carbon coating; (S2) Alloying the (quasi-) metal oxide with lithium by mixing the lithium metal powder with the material obtained in the step (S1) and subjecting it to heat treatment; (MO _x -Li _y ) -C (where M is a number of carbon atoms) of the core-shell structure including the multi-coated shell portion, and (S3) Wherein x is greater than 0 and less than 1.5 and y is greater than 0 and less than 4, and a composite of the anode active material and the anode active material.

According to one embodiment of the present invention, the carbon material of the secondary carbon coating may comprise amorphous carbon selected from the group consisting of coal-based pitch, petroleum pitch, tar, low molecular weight heavy oil and mixtures thereof have.

Also, according to an embodiment of the present invention, the secondary carbon coating may be coated by a chemical vapor deposition (CVD) method, and the chemical vapor deposition method may be performed at a temperature of 600 to 900 ° C.

According to an embodiment of the present invention, the carbon material of the secondary carbon coating may be 1 to 15% by weight based on the weight of the negative electrode active material.

According to an embodiment of the present invention, in the lithium alloying step, the weight ratio of the material obtained in the step (S1) and the lithium metal powder may be 30:70 to 95: 5.

According to another aspect of the present invention, there is provided a negative electrode active material produced by the method of the present invention.

The present invention provides a negative electrode active material having a high capacity and a high initial efficiency as well as an excellent controllability of cycle characteristics and volume expansion.

Particularly, when the (quasi-) metal oxide-Li alloyed (MO _x -L _y ) is used as the negative electrode active material, side reactions caused by by-products that may be formed during lithium alloying can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a SEM photograph of a negative electrode active material according to Example 1 of the present invention.
2 is a SEM photograph of a negative electrode active material according to Comparative Example 1 of the present invention.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the constitutions described in the drawings are merely the most preferred embodiments, and not all of the technical ideas of the present invention are described. Therefore, various equivalents which can be substituted at the time of the present application It should be understood that variations can be made.

The negative electrode active material according to the present invention includes a core portion including (sub) metal oxide-Li alloyed (MO _x -L _y ) and a shell portion including a carbon material coated on the surface of the core portion (MO _x -Li _y ) -C composite (wherein M is a (sub) metal, x is more than 0 and less than 1.5, and y is less than 4 but less than 4) having a core- The shell portion is preferably a multi-coated shell portion including a primary carbon coating before Li alloying and a secondary carbon coating after Li alloying.

When the (manganese) metal oxide is alloyed with lithium and Mn _x Li _y is alloyed with lithium and a (quasi-) metal oxide, irreversible phases such as lithium oxide and lithium metal oxide are generated less during initial charge and discharge of the battery The initial efficiency of the negative electrode active material can be increased but lithium byproducts generated during the process of synthesizing lithium and the (quasi-) metal oxide remain on the surface of the negative electrode active material, so that it is difficult to mix the slurry of the negative electrode active material including the binder There is a problem that the adhesion of the slurry is weakened by changing the physical properties of the binder in the slurry.

Therefore, in order to solve this problem, the inventors of the present invention have found that, in addition to the primary carbon coating functioning as a lithium-reaction barrier layer capable of suppressing the rapid reaction between lithium and (quasi) metal oxide before lithium alloying, Shell structure in which the shell portion is a multi-coated shell portion by proceeding with a secondary carbon coating capable of suppressing reaction and the like which is caused by residual Li byproducts on the surface of the active material after the lithium- Of the negative active material. In particular, the present invention improves the surface of the negative electrode active material through the secondary carbon coating, thereby lowering the pH of the aqueous binder system during the production of the negative electrode, thereby suppressing changes in the physical properties of the binder in the slurry, The present invention has been completed based on the surprising discovery that an effect such as improvement can be expected.

The Li by-product according to the present invention means an unreacted lithium metal powder, a lithium silicate compound, a lithium carbonate, and a mixture thereof. As the secondary carbon coating, the reaction of Li by-products present on the surface of the negative active material can be suppressed.

In addition, the negative electrode active material of the core-shell structure, which is the multiple coated shell part according to the present invention, can be manufactured into a negative electrode according to a manufacturing method commonly used in the art, wherein a binder and a solvent If necessary, the conductive material and the dispersant may be mixed and stirred to prepare a slurry, which may then be applied to a current collector and compressed to produce an electrode. In particular, when an aqueous solvent is used as the solvent, the negative active material according to the present invention has a pH of 1 to 11, preferably 5 to 11, and is converted into a water-based active material by Li by- Thereby improving the problem of increasing the pH in the system.

In the present invention, the aqueous system refers to a system using water as a binder dispersion medium. In the aqueous system, 1 g of the active material is dispersed in distilled water, and 10 g of the active material is dispersed in a 0.1 M HCl solution This is the measured result.

Wherein the carbonaceous material is formed after the alloy of the (quasi) metal oxide and lithium of the secondary carbon coating, wherein the carbonaceous material is selected from the group consisting of coal based pitch, petroleum pitch, tar, low molecular weight heavy oil, Carbon, and it is preferable to use a carbon material as the pitch system.

Further, in the case of coating with amorphous carbon, a method of carbonizing a carbon precursor by coating with an amorphous carbon precursor and heat treating can be used. The coating method can be used both dry and wet mixing. Also, a vapor deposition method such as a chemical vapor deposition (CVD) method using a gas containing carbon such as methane, ethane, propane, ethylene, acetylene and the like may be used, among which a chemical vapor deposition method is most preferable. The temperature at this time is preferably 900 ° C or less, preferably 600 to 900 ° C. This is because heat treatment at a temperature higher than 900 ° C increases the crystallinity of Si and deteriorates the performance of the negative electrode active material. When the heat treatment is performed at a temperature lower than 600 ° C, And the coating can not be performed by the chemical vapor deposition method.

The carbon material of the secondary carbon coating may be 1 to 15 wt% based on the weight of the negative electrode active material. Side reaction with the aqueous binder by the secondary carbon coating can be suppressed when the content is in the above range.

In addition, the primary carbon coating material according to the present invention is formed before the alloying of lithium and (sub) metal oxide and has a lithium-reactive barrier layer capable of inhibiting rapid reaction between lithium and (sub) Lt; / RTI >

The carbon material of the primary carbon coating may be crystalline carbon, amorphous carbon or a mixture thereof. The carbon material of the shell portion may be used in an amount of about 0.05 to about 20 wt% based on the weight of the negative electrode active material.

When the primary carbon coating is not performed, the reaction between the lithium metal powder, for example, the lithium metal and the (quasi-) metal oxide is not controlled, so that the metal crystal phase in the (quasi-) metal oxide grows rapidly. The growth of such a metal crystal phase may cause stress to occur due to the volume expansion due to the weak ionic bond between the metal and the lithium, so that cracks may easily occur. Such cracks may occur irregularly, which may result in a portion of the material not contacting the electrolyte or an electrically isolated portion, which may lead to a failure of the battery.

In the case of the carbon material of the primary carbon coating layer, in the case of the crystalline carbon, the core portion and the crystalline carbon may be mixed in a solid or liquid state, and then the coating may be performed to coat the core portion with the crystalline carbon.

In case of mixing in solid phase, coating can be carried out mainly by mechanical mixing method. Examples of the mechanical mixing method include a kneading method and a mixer for shear stress during mixing. A mechanochemical method of inducing fusion between material surfaces by applying mechanical intermixing or mechanically intermaterial shear force to the wing structure of the wing.

In the case of mixing in a liquid phase, mixing can be carried out mechanically in a similar manner to mixing in a solid phase, or by spray drying, spray pyrolysis, or freeze drying. In the case of liquid phase mixing, water, an organic solvent or a mixture thereof may be used as the solvent to be added, and ethanol, isopropyl alcohol, toluene, benzene, hexane, tetrahydrofuran and the like may be used as the organic solvent.

In the case of coating with amorphous carbon, a method of carbonizing the carbon precursor by coating with an amorphous carbon precursor and heat treatment may be used. The coating method can be used both dry and wet mixing. In addition, a vapor deposition method such as a chemical vapor deposition (CVD) method using a gas including carbon such as methane, ethane, propane, ethylene, acetylene, etc. may also be used. Examples of the amorphous carbon precursor include resins such as phenol resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan resin, cellulose resin, epoxy resin and polystyrene resin, coal pitch, petroleum pitch, tar ) Or a low molecular weight heavy oil can be used.

Hereinafter, the core portion according to the present invention will be described in detail. The core part according to the invention comprises an oxide of a (sub) metal. The metal may be selected from the group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, Ti, Ga and alloys thereof but is not limited thereto. The (sub) metal (s) are present in the core portion in the form of oxides. Preferably, the oxide of the (quasic) metal is not limited to one kind of compound selected from the group consisting of SiO, SnO and SnO ₂ , or a mixture of the two. In order to control the content of oxygen of the (sub) metal oxide of the final product, it may further comprise a (sub) metal such as the above-mentioned (sub) metal.

The core portion may have a diameter of about 0.05 to about 30 탆, or about 0.5 to about 15 탆.

The thus-prepared negative electrode active material of the present invention can be manufactured into a negative electrode according to a manufacturing method commonly used in the art.

For example, the electrode active material of the present invention can be prepared by mixing and stirring a binder and a solvent, if necessary, with a conductive material and a dispersing agent to prepare a slurry, applying the slurry to a current collector, and compressing the electrode. In particular, the negative electrode active material according to the present invention solves the problem that the pH is increased, which may be caused by Li by-products in an aqueous binder containing water as a dispersion medium. Also, the anode according to the present invention can be produced by a conventional method in the art, like the cathode.

As the binder, polyvinylidene fluoride-co-hexafluoro propylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride- Polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate (also referred to as polyvinylpyrrolidone), polyvinylpyrrolidone polyvinyl acetate, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate ), Cyanoethylpullulan, cyanoethyl But are not limited to, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose (CMC), acrylonitrile-styrene-butadiene But are not limited to, those selected from the group consisting of acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidenefluoride, polyacrylonitrile, and styrene butadiene rubber (SBR) Or a mixture of two or more thereof.

As the cathode active material, a lithium-containing transition metal oxide may be preferably used. For example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO _{2 x <1.3), Li x Mn} 2 O 4 (0.5 <x <1.3), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, Li _x Co _{1- y} Mn _y O ₂ (where 0 <c <1, a + b + c = 1), Li _x Ni _1-y Co _y O ₂ 0.5 <x <1.3, 0≤y < 1), Li x Ni 1 -y Mn y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 ( (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Li _x Mn _{2 -z} Ni _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ (0.5 <z <2), Li _x Mn _{2 -z} Co _z O ₄ x < 1.3), or a mixture of two or more thereof. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also 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 ^- .

As the organic solvent contained in the electrolytic solution used in the present invention, the organic solvent commonly used in the electrolyte for a lithium secondary battery can be used without limitation, and examples thereof include propylene carbonate (PC), ethylene carbonate (ethylene carbonate) EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxy But are not limited to, ethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, fluoro-ethylene carbonate (FEC) and propionate esters such as methyl- Methyl-propionate, ethyl-propionate, propyl-propylate, Carbonate (propyl-propionate), Butyl-like propionate (butyl-propionate) or any mixture of two or more of those selected from the group consisting of the like can be used as a representative. 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.

Optionally, the separator may further comprise a porous coating layer on its surface. The porous coating layer includes inorganic particles and a binder. The binder is located on a part or all of the inorganic particles, and functions to connect and fix the inorganic particles.

The inorganic particles may be inorganic particles having a dielectric constant of about 5 or more, or inorganic particles having a lithium ion transporting ability (in the case of a lithium secondary battery), either singly or in combination. The dielectric constant of about 5 or more inorganic _{particles, BaTiO 3, Pb (Zr x} , Ti 1 -x) O 3 (PZT, 0 <x <1), Pb 1 - x La x Zr 1 -y Ti y O 3 (PMN-PT, 0 < x < 1), (1-x) Pb (Mg _1/3 Nb _2/3 ) O _3-x PbTiO ₃ (PLZT, 0 <x < Wherein the metal oxide selected from the group consisting of hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC and TiO ₂ Or a mixture of two or more thereof. The inorganic particles having lithium ion transferring ability include, but are not limited to, lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x < lithium aluminum titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2, 0 <y <1, 0 <z <3) (LiAlTiP) x O y series glass (glass), (0 < x <4, 0 <y < 13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2,0 <y <3), lithium germanium thiophosphate Mani Titanium (Li _x Ge _y P _z S _{w, 0 <x <4,} 0 <y <1, 0 <z <1, 0 <w <5), lithium nitrides _{(Li x N y, 0 <} x <4, 0 <y <2), SiS _{2 (Li x Si y S z} , 0 <x <3,0 <y <2,0 <z <4) based glass, and _{P 2 S 5 (Li x P} y S z, 0 <x <3, 0 < y <3, 0 <z <7) series glass, or a mixture of two or more thereof. The average particle size of the inorganic particles is not particularly limited, but may range from about 0.001 탆 to about 10 탆 for the formation of a porous coating layer of uniform thickness and proper porosity. When the average particle diameter of the inorganic particles satisfies the above range, the dispersibility of the inorganic particles can be prevented from decreasing, and the porous coating layer can be adjusted to an appropriate thickness.

The binder may be included in an amount of about 0.1 to about 20 parts by weight, preferably about 1 to about 5 parts by weight, based on 100 parts by weight of the total amount of the binder and the inorganic particles. Non-limiting examples thereof include polyvinylidene fluoride-co-hexafluoro propylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloroethylene Polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, poly (vinylpyrrolidone), polyvinylpyrrolidone, But are not limited to, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate cellulose acetate propionate, cyanoethylpullulan, But are not limited to, polyvinylpyrrolidone, polyvinyl alcohol, cyanoethylpolyvinylalcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose (CMC), acrylonitrile-styrene Acrylonitrile-styrene-butadiene copolymer, polyimide, polyvinylidene fluoride, polyacrylonitrile, and styrene butadiene rubber (SBR). Any one selected or a mixture of two or more thereof.

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.

Hereinafter, a method of manufacturing the negative electrode active material according to another aspect of the present invention will be described. A method of manufacturing an anode active material according to the present invention includes the steps of: (S1) applying a first carbon coating to a surface of a core portion containing an oxide of a (sub) metallic; (S2) Alloying the (quasi-) metal oxide with lithium by mixing the lithium metal powder with the material obtained in the step (S1) and subjecting it to heat treatment; (MO _x -Li _y ) -C (where M is a number of carbon atoms) of the core-shell structure including the multi-coated shell portion, and (S3) Wherein x is greater than 0 and less than 1.5, and y is greater than 0 and less than 4, to form a negative electrode active material.

The core portion and the shell portion are as described above with respect to the negative electrode active material.

The step of performing the primary carbon coating on the surface of the core portion containing the oxide of the (S1) (sub) metal is performed before the alloying of the lithium and the (sub) metal oxide.

As the carbon material of the primary carbon coating, crystalline carbon, amorphous carbon or a mixture thereof may be used. The carbon material of the shell portion may be about 0.05 to about 20 wt% based on the weight of the negative electrode active material.

In the case of the carbon material of the primary carbon coating layer, in the case of the crystalline carbon, the core portion and the crystalline carbon may be mixed in a solid or liquid state, and then the coating may be performed to coat the core portion with the crystalline carbon.

In case of mixing in solid phase, coating can be carried out mainly by mechanical mixing method. Examples of the mechanical mixing method include a kneading method and a mixer for shear stress during mixing. A mechanochemical method of inducing fusion between material surfaces by applying mechanical intermixing or mechanically intermaterial shear force to the wing structure of the wing.

In the case of mixing in a liquid phase, mixing can be carried out mechanically in a similar manner to mixing in a solid phase, or by spray drying, spray pyrolysis, or freeze drying. In the case of liquid phase mixing, water, an organic solvent or a mixture thereof may be used as the solvent to be added, and ethanol, isopropyl alcohol, toluene, benzene, hexane, tetrahydrofuran and the like may be used as the organic solvent.

In the case of coating with amorphous carbon, a method of carbonizing the carbon precursor by coating with an amorphous carbon precursor and heat treatment may be used. The coating method can be used both dry and wet mixing. In addition, a vapor deposition method such as a chemical vapor deposition (CVD) method using a gas including carbon such as methane, ethane, propane, ethylene, acetylene, etc. may also be used. Examples of the amorphous carbon precursor include resins such as phenol resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan resin, cellulose resin, epoxy resin and polystyrene resin, coal pitch, petroleum pitch, tar ) Or a low molecular weight heavy oil can be used.

(S2), the lithium metal powder is mixed with the material obtained in the step (S1) and the lithium metal is alloyed with the (sub) metal oxide by heat treatment. The complex formed in step (S1) is mixed with the lithium metal powder by a chemical mixing method, a mechanical mixing method, a dry mixing method, or the like.

In the case of the chemical mixing method, the lithium metal powder may be prepared by preparing a dispersion using a solvent and / or a dispersion medium, mixing the composite in the dispersion, and then subjecting the mixture to heat treatment to obtain a final negative electrode active material.

There is no particular limitation on the solvent or dispersion medium, and it is preferable that the dissolution and mixing can be made uniformly and then can be easily removed. Non-limiting examples of the solvent or dispersion medium include xylene such as p-xylene, hexane such as heptane and n-hexane, toluene, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, - pyrrolidone, cyclohexane, dichloromethane, dimethylsulfoxide, acetonitrile, pyridine, amines, etc., or a mixture thereof.

When the lithium metal powder is dispersed in such a solvent or dispersion medium to form a dispersion and the (sub) metal oxide is further mixed into the dispersion to form a mixture, a (quasi-) So that the metal oxide can be dispersed. The dispersion apparatus is not particularly limited as long as it is an apparatus for dispersing a substance to be dispersed in a solvent or a dispersion medium. Examples thereof include an ultrasonic dispersion apparatus, a magnetic stirling apparatus, and a spray dryer apparatus.

Thereafter, the solvent or dispersion medium is removed by drying the formed dispersion at room temperature of about 25 to about 28 DEG C or at a temperature of about 50 to about 200 DEG C to obtain a mixture of the composite and lithium metal powder. However, the method for removing the solvent or the dispersion medium may use methods known in the art.

In addition, the lithium metal powder and the composite can be uniformly mixed using a mechanical mixing method. Here, the mechanical mixing is to apply a mechanical force to crush and mix materials to be mixed to form a uniform mixture.

In general, the mechanical mixing is performed mechanically such as a high energy ball mill using a chemical inert bead, a planetary mill, a stirred ball mill, a vibrating mill, In the mixing apparatus, process parameters such as rotation speed, ball-powder weight ratio, ball size, mixing time, mixing temperature and atmosphere can be changed. At this time, alcohol such as ethanol and higher fatty acid such as stearic acid may be added as a processing control agent in order to obtain a good mixing effect. The process control agent may be added in an amount of about 2.0 parts by weight or less, preferably 0.5 parts by weight or less, based on 100 parts by weight of the mixture. When the process control agent is added, the mixing time can be reduced.

In addition, in the mechanical mixing method, when the conditions such as mixing time, mixing temperature, and rotation speed are changed by increasing the rotation speed at a high temperature for a long time, the lithium metal powder and the composite are crushed and mixed, alloying processing can be performed. Through the mechanical mixing and the mechanical alloying process, the present invention can obtain an electrode active material in the form of an alloy having a uniform composition. In this case, the heat treatment in an inert atmosphere may not be performed later.

In addition, the lithium metal powder and the composite can be simply and dryly mixed, in which case the mixing equipment can be used without limitation as long as it is commonly known in the art. For example, a shaker, a stirrer, or the like may be used. Following this mixing step, a conventional heat treatment step follows.

The complex formed in the step (S1) and the lithium metal powder are mixed so that the weight ratio is about 70:30 to about 98: 2. This mixing ratio is a set value because lithium is a very light metal and is difficult to mix in excess of the weight ratio described above with respect to the composite.

When the weight ratio of the lithium metal powder is less than 2, the content of lithium in the final product is too small and the initial efficiency is not so high. On the other hand, when the weight ratio of the lithium metal powder is more than 30, lithium oxide or lithium silicate, which is inactive phases, is excessively produced in the final product, and the discharge capacity per unit weight is reduced. The metal part can cause a reaction to alloy with lithium. Such lithium oxide or lithium silicate is a relatively stable phase, but a lithium- (quasi-) metal compound such as a Li-Si compound becomes unstable when left outside. For example, when mixing about 10% by weight of the lithium metal powder with the composite, the initial efficiency may be close to 90%.

The (sub) metal oxide-Li alloying is achieved in the core portion by heat-treating the mixture thus formed. In order to form a lithium alloy with lithium metal powder in the core portion, the primary carbon coating layer of the composite formed in the step (S1) must be present as a carbon material. The reason for this is as described above with respect to the negative electrode active material herein.

The mixture of the complex formed in step (S1) and the lithium metal powder requires a heat treatment to form a (quasi-) metal oxide-Li alloy.

When the mixture is heat-treated in an inert atmosphere in the reactor, the (quasi-) metal oxide and lithium react with each other to form new bonds, wherein lithium may exist in the form of lithium oxide or lithium (quasi) metal oxide.

In this case, the heat treatment temperature range is not particularly limited as far as it is the temperature between the melting point of the lithium metal powder and the boiling point of the lithium metal powder. If the melting point of the lithium metal powder is less than the melting point of the lithium metal powder, the reaction between the lithium metal powder and the (quasi-) metal oxide may not occur. If the boiling point of the lithium metal powder is exceeded, The lithium metal powder can be evaporated in the form of a gas. Accordingly, the heat treatment temperature range is preferably about 500 to about 2,000 DEG C, or about 700 to about 1,200 DEG C. [

For example, when the mixture is mixed with SiO, which is a (quasi-) metal oxide, and the mixture is heat-treated, a temperature of about 1,100 ° C or lower is preferable. This is because the SiO ₂ tends to grow separately from SiO ₂ and SiO ₂ at a temperature higher than 1,100 ° C., and the advantage of volume control of SiO ₂ can be reduced. Therefore, the heat treatment is preferably carried out at a temperature between the melting point of the lithium metal powder and the boiling point of the lithium metal powder, wherein the kind of the (sub) metal oxide is preferably taken into consideration.

The heat treatment is preferably performed in an inert gas atmosphere in which nitrogen gas, argon gas, helium gas, krypton gas, or xenon gas is present in order to block contact with oxygen. If the mixture comes into contact with oxygen at the time of heat treatment of the mixture, the lithium source and oxygen react with the metal oxide together to form lithium oxide or lithium metal oxide, so that the initial efficiency increase effect of the battery can be reduced.

In this (sub) metal oxide-Li alloy, the oxygen content of the (sub) metal oxide is MO _x (0 <x <1.5) ) Is relatively small, which may cause a reduction in the total energy density, and may also cause a problem of lowering the initial efficiency.

The surface of the (quasi) metal oxide core part of the present invention is provided with a shell part which is a coating layer of carbon material. The primary carbon layer shell part of the carbon material passes lithium but interferes with the passage of oxygen, Quasi-metal oxide, it is easy to control the oxygen content of the (quasi-) metal oxide.

If necessary, the surface of the composite formed in step (S2) may be washed and dried. This is because the unreacted lithium metal powder remains on the surface of the composite or by-products due to the side reaction between the lithium metal powder and the (quasi-) metal oxide may remain.

However, in spite of such a washing reaction, there is a possibility that by-products which can not be removed exist, so that the present invention is to suppress the reaction of these by-products through a step of coating the material obtained in the step (S2) with a secondary carbon .

Wherein the carbon material is selected from the group consisting of a coal-based pitch, a petroleum pitch, tar, a low molecular weight heavy oil, and mixtures thereof after the secondary carbon coating of the (quasi-) metal oxide and the lithium alloy Amorphous carbon may be used. Of these, it is preferable to use a carbon material as the pitch system.

Further, in the case of coating with amorphous carbon, a method of carbonizing a carbon precursor by coating with an amorphous carbon precursor and heat treating can be used. The coating method can be used both dry and wet mixing. In addition, a vapor deposition method such as a chemical vapor deposition (CVD) method using a gas containing carbon such as methane, ethane, propane, ethylene, acetylene, etc. may be used. Of these, the chemical vapor deposition method is most preferable. Or less, preferably 600 to 900 占 폚. This is because, when the heat treatment is performed at a temperature higher than 900 ° C., the crystallinity of Si is increased and the performance of the negative electrode active material is deteriorated.

The carbon material of the secondary carbon coating may be 1 to 15% by weight based on the weight of the negative electrode active material.

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.

Example

Example  One

10 g of SiO 2 having an average particle diameter of 5 탆 as a (quasi-) metal oxide was charged into a rotating tubular furnace, and then argon gas was flowed at 0.5 L / min, and then the temperature was raised to 1,000 캜 at a rate of 5 캜 / min. The rotary tubular furnace was rotated at a rate of 10 rpm / min while flowing argon gas at 1.8 L / min and acetylene gas at 0.3 L / min, and then subjected to heat treatment for 2 hours to form a primary carbon coating layer Was prepared. Here, the carbon content of the primary carbon coating layer was 5.3 parts by weight based on 100 parts by weight of the core portion. Also, the thickness of the primary carbon coating layer was observed to be 40 nm from the TEM analysis.

The prepared composite was mixed with a lithium metal powder in a weight ratio of 92: 8 to form a mixture. The mixture was heat-treated at 700 캜 for 5 hours in an Ar atmosphere to alloy the core with lithium.

Further, the material obtained above was charged into a rotating tubular furnace, and the temperature was raised to 900 DEG C at a rate of 5 DEG C / minute while introducing argon gas at 1.0 L / min. The secondary tubular carbon coating was carried out by flowing the argon gas at 1.8 L / min and the acetylene gas at 0.3 L / min while rotating the rotating tubular body at a speed of 10 rpm / min for 3 hours to form a core- (MO _x -Li _y ) -C composite anode active material having the structure of Here, the carbon content of the secondary carbon coating layer was 10 parts by weight based on 100 parts by weight of the core portion. In addition, the thickness of the primary carbon coating layer was observed to be 90 nm from the TEM analysis. In the composition of the negative active material, that is, in the formula (MO _x -L _y ) -C, it was confirmed that 0 <x <1.5 and 0 <y <4 in the measurement results.

1 is a SEM photograph of a negative electrode active material according to Example 1 of the present invention.

Comparative Example  One

A carbon material was coated on the (quasi-) metal oxide powder (SiO, D ₆₀ = 5 μm) in the same manner as in Example 1, except that the process of coating the secondary carbon coating layer in Example 1 was performed, To prepare an active material.

2 is a SEM photograph of a negative electrode active material according to Comparative Example 1 of the present invention.

Test Example

The anode active material prepared in Example 1 and Comparative Example 1 and graphite were mixed at a weight ratio of 15:85, and carbon black and SBR / CMC were mixed as a conductive agent in a weight ratio of 94: 2: 2: 2 Respectively. These were mixed in distilled water as a solvent and mixed to prepare a uniform electrode slurry. The pH was measured by titrating 0.1 M HCl to pH 4 in a solution of 1 g of the active material dispersed in 10 g of tertiary distilled water and filtering the solution. In the case of Example 1, the pH was 8, and the pH according to Comparative Example 1 was 12.

Claims (21)

Core-shell structure comprising a core including a quasi-metal oxide-Li alloying (MO _x -L _y ) and a shell including a carbon material coated on a surface of the core, shell structure (MO _x -Li _y ) -C composite wherein M is a (sub) metal, x is more than 0 and less than 1.5, and y is less than 4 but less than 4) . The method according to claim 1,
Wherein the shell portion is a multi-coated shell portion including a primary carbon coating before Li alloying and a secondary carbon coating after Li alloying. The method according to claim 1,
Wherein the shell portion is not exposed to the surface of the lithium by-product comprising the lithium metal powder, the lithium silicate compound, the lithium carbonate, and the mixture thereof. The method according to claim 1,
Wherein the negative electrode active material has a pH of 1 to 11 in an aqueous system. 3. The method of claim 2,
Wherein the carbon material of the secondary carbon coating comprises amorphous carbon selected from the group consisting of coal-based pitch, petroleum pitch, tar, low molecular weight heavy oil, and mixtures thereof. 3. The method of claim 2,
Wherein the secondary carbon coating is coated by a chemical vapor deposition (CVD) method. 3. The method of claim 2,
Wherein the carbon material of the secondary carbon coating is 1 to 15 wt% based on the weight of the negative electrode active material. 3. The method of claim 2,
Wherein the carbon material of the primary carbon coating is crystalline carbon, amorphous carbon or a mixture thereof. 3. The method of claim 2,
Wherein the carbon material of the primary carbon coating is 0.05 to 20 wt% of the weight of the negative electrode active material. The method according to claim 1,
Wherein the (quasi) metal is 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 (quasi-) metal oxide is one kind of compound selected from the group consisting of SiO, SnO and SnO ₂ , or a mixture of the two. The method according to claim 1,
And the core portion has a diameter of 0.05 to 30 占 퐉. And a negative electrode active material layer formed on at least one side of the current collector and including the negative electrode active material according to any one of claims 1 to 12. 12. A negative electrode for a lithium secondary battery comprising: 13. A lithium secondary battery comprising a positive electrode, a negative electrode according to claim 13, and a separator interposed between the positive electrode and the negative electrode. (S1) applying a primary carbon coating to a surface of a core portion containing an oxide of a (quasi) metal;
(S2) Alloying the (quasi-) metal oxide with lithium by mixing the lithium metal powder with the material obtained in the step (S1) and subjecting it to heat treatment; And
(S3) coating the surface of the material obtained in the step (S2) with a secondary carbon coating.
(MO _x -Li _y ) -C (where M is a (sub) metal, x is more than 0 and less than 1.5, y is more than 0 and less than 4) of a core-shell structure comprising multiple coated shell portions, By weight based on the total weight of the negative electrode active material. 16. The method of claim 15,
Wherein the carbon material of the secondary carbon coating comprises amorphous carbon selected from the group consisting of coal-based pitch, petroleum pitch, tar, low molecular weight heavy oil, and mixtures thereof. 16. The method of claim 15,
Wherein the secondary carbon coating is coated by a chemical vapor deposition (CVD) method. 16. The method of claim 15,
Wherein the chemical vapor deposition method is performed at a temperature of 600 to 900 占 폚. 16. The method of claim 15,
Wherein the carbon material of the secondary carbon coating is 1 to 15 wt% based on the weight of the negative electrode active material. 16. The method of claim 15,
In the lithium alloying step, the weight ratio of the material obtained in the step (S1) and the lithium metal powder is 30:70 to 95: 5. 20. A negative electrode active material produced by the method for producing a negative active material as defined in any one of claims 15 to 20.

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