KR20130117714A - Electrode active material having improved lithium diffusivity and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An electrode active material is provided to make a defect in parts of the layered crystal structure within a carbon coating layer, thereby improving electric conductivity and lithium ion conductivity. CONSTITUTION: A carbon coating layer having a lithium movement channel is formed on the surface of the lithiated metal oxide with a spinel structure which inserts and separates the lithium ions while charging and discharging. The lithiated metal oxide is expressed as LixMyMn(2-y)O(4-z)Az represented by the chemical formula 1. In the chemical formula 1, it is 0.9<=x<=1.2, 0<y<2, 0<=z<0.2. M is selected from a group comprising Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi. A is at least one anion of -1 or -2.

Description

Electrode active material with improved lithium diffusivity and lithium secondary battery comprising same {Electrode Active Material Having Improved Lithium Diffusivity and Lithium Secondary Battery Comprising The Same}

The present invention relates to a secondary battery capable of repeated charging and discharging and an electrode active material constituting the secondary battery.

The increase in the price of energy sources due to the depletion of fossil fuels, the increase of interest in environmental pollution, and the demand for environmentally friendly alternative energy sources are becoming indispensable factors for future life. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, in the case of a lithium secondary battery, the demand for an energy source is rapidly increasing due to an increase in technology development and demand for a mobile device. Recently, the use of a lithium secondary battery as a power source for an electric vehicle (EV) and a hybrid electric vehicle , And the area of use is also expanding for applications such as power assisted power supply through gridization.

Lithium secondary batteries include a lithium-containing cobalt oxide such as LiCoO ₂ having a layered structure, a lithium-containing nickel oxide such as LiNiO ₂ having a layered crystal structure, or a LiMn ₂ O ₄ having a spinel crystal structure as a positive electrode active material. Such as lithium-containing manganese oxides.

The lithium-containing manganese oxide of the spinel crystal structure has poor electrical conductivity and poor conductivity due to a long diffusion path of lithium ions due to its steric structure.

Carbon coatings are widely used to improve electrical conductivity.

As the negative electrode of the conventional lithium secondary battery, a carbon-based compound capable of reversible intercalation and desorption of lithium ions while maintaining structural and electrical properties is mainly used as a negative electrode active material. A lot of researches on a negative electrode material and lithium titanium oxide by the Li alloy reaction using (Si), tin (Sn).

Lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) has a high operating voltage of 1.5 V, there is no generation of resin phase crystals (dendrite), there is little volume change during insertion / desorption of lithium ions, structurally stable, It is known to have excellent rate and life characteristics.

Lithium titanium oxide has disadvantages of low electrical conductivity, high speed charging and discharging, and low output density per volume.

In addition, the theoretical capacity of the lithium titanium oxide is 175 mAh / g, even though the capacity is improved to the current level of 160 to 170 mAh / g, there is a problem that there is a limit of capacity compared to the conventional carbon-based negative electrode material.

When making fast charge cells, the delivery path in the electrode must be very efficient in order to allow high current to flow without side reactions.

In particular, low-thickness lithium titanium oxide requires a thick coating to make a cell having a desired capacity, and therefore an efficient electrical connection is essential. Carbon coatings are widely used to improve electrical conductivity.

Carbon coatings can speed up the transfer of electrons, but do not improve the conductivity of lithium ions.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

An object of the present invention is to provide a lithium secondary battery including an electrode active material having the same electrical conductivity and lithium ion conductivity at the same time by making a defect in a part of the layered crystal structure in the carbon coating layer.

Electrode active material according to the present invention,

A carbon coating layer having a lithium transfer channel is formed on a surface of a lithium metal oxide having a spinel structure in which lithium ions are inserted and desorbed during charging and discharging.

The carbon coating layer may include a carbon compound, and the carbon compound may include a single carbon material consisting of only a combination of carbon (C) elements, and the carbon compound may be graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; It may be one or two or more selected from the group consisting of carbon fibers and the like. However, it is not limited only to these.

In a specific embodiment of the present invention, the single carbon material may be graphite.

The coating amount of the conductive carbon coating layer may be 0.2 to 5 parts by weight per 100 parts by weight of the lithium metal oxide.

When the coating amount of the carbon coating layer is less than 0.2 part by weight per 100 parts by weight of lithium metal oxide, the desired electronic conductivity cannot be exhibited. When the coating amount of the carbon coating layer is more than 5 parts by weight, the coating layer becomes thick and the coating layer acts as a resistance. Not desirable

The carbon coating layer may have a thickness of 2 nm or more and 50 nm or less.

If it is less than 2 nm, the desired electron conductivity cannot be exhibited, and if it is more than 50 nm, the carbon coating layer may act as a resistance, which is not preferable.

The carbon coating layer includes a group 13 or 15 element on the periodic table, and specifically, the group 13 or group 15 element may replace a part of carbon of the carbon coating layer.

As a result, in the carbon coating layer, a portion of the hexagonal planes constituted by the carbon elements deviate from the planar arrangement, resulting in defects in the layered crystal structure. As a result, the passages to which the defects are connected may serve as movement paths of lithium ions. .

In a specific embodiment according to the present invention, the Group 13 element may be boron (B).

In a specific embodiment according to the present invention, the group 15 element may be nitrogen (N).

The electrode active material of the present invention may be prepared by selectively adding a carbon precursor, a Group 13 element source, and a Group 15 element source to a solvent to prepare a coating solution, then mixing lithium metal oxide into the coating solution and heat treating the mixture. have.

The carbon coating layer having the lithium transfer channel may be deposited on the surface of the lithium metal oxide by chemical vapor deposition (CVD) or physical vapor deposition (PVD). As the chemical vapor deposition method, a fluidized bed chemical vapor deposition method, a rotary three-dimensional chemical vapor deposition method, a vibration chemical vapor deposition method, etc. may be used, and as the physical vapor deposition method, sputtering, vacuum annual method, plasma coating method, or the like may be used.

In addition, the electrode active material of the present invention may be prepared by dry mixing a carbon precursor, a Group 13 element source, and a Group 15 element source with a lithium metal oxide by using a mechanofusion device, a noble device, or the like. have.

As said carbon precursor, Graphite, such as hydrocarbons, such as toluene, natural graphite, and artificial graphite; Carbon black, super-blood black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon nanotubes, carbon nanofibers, florene and the like can be used.

The Group 13 element source may be a boron compound, an aluminum compound, a gallium compound, an indium compound, or the like, and specifically, borax, boron oxide (B ₂ O ₃ ), boron-hydride (borane), triphenylboron ((C ₅ H ₅ ) ₃ B), boron halide, and the like.

The Group 15 element source may be a nitrogen compound, a phosphorus compound, or the like, and specifically, may be pyrrole, quinoline, pyridine, pyrimidine, or the like.

The present invention provides a lithium secondary battery having a structure in which an electrode assembly including the electrode active material described above and a porous polymer membrane and a polymer assembly interposed between a positive electrode and a negative electrode are housed in a battery case and sealed.

The lithium secondary battery may include a lithium salt-containing non-aqueous electrolyte.

The lithium secondary battery may be a lithium ion battery, may be a lithium ion polymer battery, may be a lithium polymer battery.

The electrode may be an anode or a cathode, and may be manufactured by a manufacturing method including the following processes.

The electrode manufacturing method,

Preparing a binder solution by dispersing or dissolving the binder in a solvent;

Preparing an electrode mixture slurry by mixing the binder solution with an electrode active material and a conductive material;

Coating the electrode mixture slurry on a current collector;

Drying the electrode; And

Compressing the electrode to a constant thickness.

In some cases, the method may further include drying the rolled electrode.

The binder solution manufacturing process is a process of preparing a binder solution by dispersing or dissolving a binder in a solvent.

The binder may be all binders known in the art, and specifically includes polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). Fluororesin binder, styrene-butadiene rubber, acrylonitrile-butadiene rubber, rubber binder including styrene-isoprene rubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose One or two or more kinds of binders selected from the group consisting of cellulose-based binder, polyalcohol-based binder, polyethylene, polyolefin-based binder including polypropylene, polyimide-based binder, polyester-based binder, mussel adhesive, and silane-based binder It may be a mixture or a copolymer.

The solvent may be selectively used according to the type of the binder. For example, an organic solvent such as isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and the like may be used.

As one specific embodiment of the present invention, PVdF may be dispersed / dissolved in NMP (N-methyl pyrrolidone) to prepare a binder solution for the positive electrode, and SBR (Styrene-Butadiene Rubber) / CMC (Carboxy Methyl Cellulose) may be used. It is also possible to prepare a binder solution for the negative electrode by dispersing / dissolving in.

An electrode mixture slurry may be prepared by mixing / dispersing an electrode active material and a conductive material in the binder solution. The electrode mixture slurry thus prepared may be transferred to a storage tank and stored until the coating process. In the said storage tank, in order to prevent an electrode mixture slurry from hardening, an electrode mixture slurry can be stirred continuously.

The electrode active material may be a positive electrode active material or a negative electrode active material.

Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

In a non-limiting embodiment of the present invention, the electrode active material may include a lithium metal oxide having a spinel structure represented by the following formula (1) as a cathode active material.

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0 < y < 2, 0 z < 0.2,

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;

A is one or more of an anion of -1 or -2.

The maximum substitution amount of A may be less than 0.2 mol%, and in a specific embodiment of the present invention, A may be at least one anion selected from the group consisting of halogen, S and N, such as F, Cl, Br, and I.

By substituting these anions, the binding force with the transition metal is improved and the structural transition of the compound is prevented, so that the lifetime of the battery can be improved. On the other hand, if the amount of substitution of the anion A is too large (t ≧ 0.2), it is not preferable because the life characteristics are lowered due to the incomplete crystal structure.

Specifically, the oxide of Formula (1) may be a lithium metal oxide represented by the following Formula (2).

Li _x Ni _y Mn _2-y O ₄ (2)

In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5.

More specifically, the lithium metal oxide may be LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ .

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, and the like.

In a non-limiting example of the present invention, the electrode active material may include a lithium metal oxide as a negative electrode active material, and the lithium metal oxide may be represented by the following general formula (3).

Li _a M ' _b O _{4-ca c} (3)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;

c is determined according to the oxidation number in the range of 0? c <0.2;

A is one or more of an anion of -1 or -2.

The oxide of formula (3) may be represented by the following formula (4).

Li _a Ti _b O ₄ (4)

In the above formula, 0.5? A? 3, 1? B? 2.5.

The lithium metal oxide may be Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, or the like. However, it is not limited only to these.

In a non-limiting embodiment of the present invention, the lithium metal oxide may be Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . Li _1.33 Ti _1.67 O ₄ has a spinel structure with little change in crystal structure during charge and discharge and excellent reversibility.

The lithium metal oxide can be produced by a production method known in the art, for example, can be produced by a solid phase method, hydrothermal method, sol-gel method and the like.

The lithium metal oxide may be in the form of secondary particles in which primary particles are aggregated.

The particle diameter of the secondary particles may be 200 nm to 30 ㎛.

If the particle size of the secondary particles is less than 200 nm, a decrease in the adhesive force in the negative electrode manufacturing process. Complementing this requires the use of more binders, which is undesirable in terms of energy density. If the particle diameter of the secondary particles is more than 30 μm, the diffusion rate of lithium ions is low, and thus it is difficult to realize high output, which is not preferable.

The lithium metal oxide may be included in more than 50% by weight or less than 100% by weight relative to the weight of the entire negative electrode active material.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

Fillers and the like may be optionally added to the electrode mixture slurry as necessary. The filler is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, etc. can be used.

The coating of the electrode mixture slurry on a current collector is a process of coating the electrode mixture slurry on a current collector in a predetermined pattern and a predetermined thickness by passing through a coater head.

The method of coating the electrode mixture slurry on the current collector, the electrode slurry may be distributed on the current collector and uniformly dispersed using a doctor blade, die casting, comma coating ( comma coating, screen printing, and the like. In addition, the electrode mixture slurry may be bonded to the current collector by pressing or lamination after molding on a separate substrate.

The current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used.

The current collector may form fine concavities and convexities on the surface to reinforce the bonding strength of the positive electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Specifically, the positive electrode current collector may be a metal current collector including aluminum, and the negative electrode current collector may be a metal current collector including copper. The electrode current collector may be a metal foil, and may be an aluminum (Al) foil or a copper (Cu) foil.

The drying process is a process of removing the solvent and water in the slurry to dry the slurry coated on the metal current collector, in a specific embodiment, is dried within 1 day in a vacuum oven of 50 to 200 ℃.

After the drying process, a cooling process may be further included, and the cooling process may be slow cooling to room temperature so that the recrystallized structure of the binder is well formed.

In order to increase the capacity density of the electrode after the coating process and to increase the adhesion between the current collector and the active materials, the electrode may be compressed into a desired thickness by passing it between two hot-rolled rolls. This process is called a rolling process.

Before passing the electrode between two hot heated rolls, the electrode can be preheated. The preheating process is a process of preheating the electrode before it is introduced into the roll in order to increase the compression effect of the electrode.

The electrode after the rolling process is completed as described above, may be dried within a day in a vacuum oven at 50 to 200 ℃ as a range satisfying the temperature of the melting point or more of the binder. The rolled electrode may be cut to a constant length and then dried.

After the drying process, a cooling process may be further included, and the cooling process may be slow cooling to room temperature so that the recrystallized structure of the binder is well formed.

The polymer membrane is a separator that separates between the positive electrode and the negative electrode. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator.

As the separator, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m.

Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like; Kraft paper and the like are used. Representative examples currently on the market include the Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation membrane to increase the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

The electrode assembly may include a jelly-roll electrode assembly (or wound electrode assembly), a stacked electrode assembly (or a stacked electrode assembly), or a stack & folding electrode assembly having a structure known in the art.

In the present specification, the stack & folding type electrode assembly is a method of folding or winding a separator sheet after arranging unit cells having a structure in which a separator is interposed between an anode and a cathode on a separator sheet. It can be understood as a concept including a stack & folding type electrode assembly to be manufactured.

In addition, the electrode assembly may include an electrode assembly having a structure in which any one of an anode and a cathode is laminated by a method such as thermal fusion in a state in which a structure is interposed between the separators.

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane A non-protonic organic solvent such as an ether, a methyl pyrophosphate, or an ethyl propionate is used as the solvent, a sulfone, a methyl sulfolane, a 1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, .

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (fluoro-ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Also, the present invention provides a battery pack including the battery module as a power source of a middle- or large-sized device, wherein the middle- or large-sized device is an electric vehicle (EV), a hybrid electric vehicle (HEV) An electric vehicle including a plug-in hybrid electric vehicle (PHEV), a power storage device, and the like, but the present invention is not limited thereto.

The structure of the battery module and the battery pack and the method of manufacturing the battery module and the battery pack are well known in the art, so a detailed description thereof will be omitted herein.

As described above, the positive electrode active material according to the present invention can secure an efficient electron transfer path in the electrode for flowing high current without side reactions, and can secure a movement path of lithium ions.

Therefore, the lithium secondary battery including the cathode active material can exhibit high rate charge / discharge characteristics.

1 is a comparative test result comparing the high rate charge and discharge characteristics of the non-limiting examples and comparative examples according to the present invention.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Pyridine was coated on the surface of LiNi _0.5 Mn _1.5 O ₄ using chemical vapor deposition (CVD) to prepare an electrode active material.

Electrode active material: Super-P: PVDF amount was measured to be 90: 5: 5: and then mixed in the mixer to mix to prepare an electrode mixture, the positive electrode mixture in a 20 ㎛ aluminum foil to 80 ㎛ thickness After coating, the porosity was rolled to 40% and dried at 60 ° C. for 24 hours to prepare a working electrode.

Lithium metal is used as a counter electrode, and as a separator, a carbonate electrolyte in which 1 mol of LiPF ₆ is dissolved in a polyethylene film (Celgard, thickness: 20 μm) and an electrolyte, and the amount of EC: DMC: EMC is 1: 1: 1 is used. A coin-type battery (N-doped C coating) was produced.

&Lt; Comparative Example 1 &

A C coating was manufactured in the same manner as in Example 1 except that toluene was coated on the surface of LiNi _0.5 Mn _1.5 O ₄ by chemical vapor deposition (CVD).

Comparative Example 2

A battery was fabricated in the same manner as in Comparative Example 1 except that no carbon coating layer was formed on the LiNi _0.5 Mn _1.5 O ₄ surface.

<Experimental Example 1>

Charge and discharge tests were carried out for 8 times while charging the cells of Example 1, Comparative Example 1 and Comparative Example 2 at a charge current of 0.1 C at a temperature of 25 ° C., and changing the discharge current to 0.1 C, 0.5 C, 1.0 C. Was performed. Figure 1 shows the initial cycle discharge capacity compared to the 0.1C capacity of the first cycle.

Referring to FIG. 1, it can be seen that Example 1 exhibits higher capacity retention than Comparative Example 1 and Comparative Example 2 during high rate discharge.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (18)

An electrode active material, wherein a carbon coating layer having a lithium transfer channel is formed on a surface of a lithium metal oxide having a spinel structure in which lithium ions are inserted and desorbed during charging and discharging. The electrode active material according to claim 1, wherein the lithium metal oxide is represented by the following general formula (1):
Li _x M _y Mn _{2 - y} O _{4 - z z} (1)
Wherein 0 < y < 2, 0 z < 0.2,
M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, ;
A is one or more of an anion of -1 or -2. The electrode active material according to claim 2, wherein the oxide of formula (1) is represented by the following formula (2):
Li _x Ni _y Mn _2-y O ₄ (2)
Wherein 0.9 ≦ x ≦ 1.2, 0.4 ≦ y ≦ 0.5; The electrode active material of claim 3, wherein the lithium metal oxide is LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ . The electrode active material according to claim 1, wherein the lithium metal oxide is represented by the following general formula (3):
Li _a M ' _b O _{4-ca c} (3)
In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;
a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4;
c is determined according to the oxidation number in the range of 0? c <0.2;
A is one or more of an anion of -1 or -2. The electrode active material according to claim 5, wherein the oxide of formula (3) is represented by the following formula (4):
Li _a Ti _b O ₄ (4)
In the above formula, 0.5? A? 3, 1? B? 2.5. The electrode active material of claim 6, wherein the lithium metal oxide is Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . The electrode active material of claim 1, wherein the carbon coating layer comprises a carbon compound. The method of claim 8, wherein the carbon compound is one, two or more selected from the group consisting of graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber. An electrode active material. The electrode active material according to claim 1, wherein the carbon coating layer comprises a Group 13 or Group 15 element on the periodic table. The electrode active material according to claim 10, wherein the Group 13 or Group 15 element of the periodic table is substituted for a part of the carbon of the carbon coating layer. The electrode active material according to claim 11, wherein the Group 13 element is boron (B). The electrode active material according to claim 11, wherein the Group 15 element is nitrogen (N). A lithium secondary battery comprising an electrode assembly including an electrode active material according to any one of claims 1 to 13 and a polymer membrane, and an electrode assembly having a structure in which a polymer membrane is interposed between a positive electrode and a negative electrode. The lithium secondary battery of claim 14, wherein the lithium secondary battery is a lithium ion battery. The lithium secondary battery according to claim 14, wherein the lithium secondary battery is a lithium ion polymer battery. The lithium secondary battery of claim 14, wherein the lithium secondary battery is a lithium polymer battery. The electrode active material according to claim 1, wherein the carbon coating layer has a thickness in a range of 2 nm or more and 50 nm or less.

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