KR101572827B1 - Cathode Material with Improved Conductivity and Lithium Secondary Battery Containing the Same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery comprising a lithium-transition metal oxide, wherein a composite (carbon-carbon composite) of oxygen (O) or sulfur (S) And the compound-carbon composite is chemically bonded to the surface of the lithium transition metal oxide.

The cathode active material according to the present invention is characterized in that the carbon-based particles are chemically bonded to the lithium-transition metal oxide by an oxygen or a sulfur compound so that not only the ion conductivity and the electric conductivity can be greatly improved but also the surface of the cathode active material and the electrolyte The reactivity with the electrolytic solution can be minimized, and therefore, there is an advantage that the stability and the high-temperature safety are excellent.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material having improved conductivity and a lithium secondary battery including the same,

The present invention relates to a positive electrode active material having improved conductivity and a lithium secondary battery comprising the same, and more particularly, to a positive electrode active material for a lithium secondary battery comprising a lithium transition metal oxide, wherein the lithium transition metal oxide has an oxygen or sulfur compound Carbon composite is coated with a composite of carbon-based particles ('compound-carbon composite'), and the compound-carbon composite is chemically bonded to the surface of the lithium transition metal oxide.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing.

In particular, as interest in environmental issues grows, research on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . Nickel metal hydride secondary batteries are mainly used as power sources for such electric vehicles, but researches on the use of lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and some of them are in the commercialization stage.

In such a lithium secondary battery, a carbon material is mainly used as a negative electrode active material, and the use of lithium metal, a sulfur compound, etc. is also considered. In addition, lithium cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material, and lithium manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, lithium nickel oxide (LiNiO ₂ ) Lithium transition metal oxides have been used.

However, the lithium transition metal oxide used as the cathode active material has a low electric conductivity, and there is also a problem that the charge / discharge rate characteristic is not sufficiently high due to the low ion conduction property which is exhibited by using the non-aqueous electrolyte.

In order to solve such problems, some prior arts have proposed a technique of coating or surface-treating an active material surface of a positive electrode with a predetermined material. For example, there is known a method of coating a conductive polymer on a cathode active material by coating a cathode active material with a conductive material to lower the contact interface resistance between the cathode active material and an electrolyte or a by-product produced at a high temperature. However, a cathode active material exhibiting sufficient battery characteristics has not been developed.

Further, since the high energy density means that the high energy density can be exposed to the high risk at the same time, there is a problem that the higher the energy density, the higher the risk of ignition and explosion.

Therefore, although many studies have been carried out in various approaches, they have not yet achieved satisfactory results. Safety has become a bigger problem due to the increase of energy density due to the complexization and multi-functionalization of mobile devices, and the rate characteristics of lithium secondary batteries have to be further improved due to demands of electric vehicles, hybrid electric vehicles and power tools .

However, it is very difficult to improve both safety and rate characteristics at the same time, and research on this has not been done yet.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that when a composite of an oxygen or sulfur compound and a carbon-based particle is applied to the surface of a lithium transition metal oxide to prepare a cathode active material, improvement in electrical conductivity and ionic conductivity The present invention has been accomplished on the basis of discovering that it is possible to improve stability and high-temperature safety while exhibiting excellent rate characteristics.

Therefore, the positive electrode active material for a lithium secondary battery comprising the lithium transition metal oxide according to the present invention is characterized in that a composite of the oxygen or sulfur compound and the carbon-based particle ('compound-carbon composite') is coated on the surface of the lithium transition metal oxide, The compound-carbon composite is chemically bonded to the surface of the lithium transition metal oxide.

There has been known a technique of adding conductive carbon to an electrode slurry for improving electrical conductivity of a lithium transition metal oxide or a technique of simply mixing mechanically a conductive carbon with a surface of a lithium transition metal oxide to make it into a contact state. This is because it is very difficult to chemically bond the oxide to the conductive carbon in the process. Thus, although a technique for depositing carbon in a gas atmosphere for chemical bonding between conductive carbon and oxide has been disclosed, the application to the mass production process is limited and the practical application is impossible.

On the other hand, since the cathode active material of the present invention is chemically bonded to the lithium transition metal oxide by the oxygen or sulfur compound, the ionic conductivity and the electric conductivity of the carbon-based particle can be greatly improved, and the surface of the cathode active material and the electrolyte The reactivity with the electrolyte can be minimized, and the stability and high-temperature safety are excellent. Hereinafter, the present invention will be described in detail.

As the cathode active material according to the present invention, the surface of the lithium transition metal oxide is coated with a composite of oxygen (O) or a sulfur (S) compound and carbon-based particles ('compound-carbon composite'), And is chemically bonded to the surface of the transition metal oxide.

The oxygen (O) or sulfur (S) compound in the compound-carbon composite can chemically bind the surface of the lithium-transition metal oxide with the carbon-based particle. Therefore, the conductive path of the carbon-based particles can be maintained very stably and reliably, so that the conductivity and the rate characteristic can be greatly improved.

In the present invention, the term "chemically bonded" means that chemical properties such as van der Waals attraction are not in contact with each other through unchanging reversible bonds, but are bonded by chemical bonds such as ionic bonds or covalent bonds.

In the present invention, the oxygen or sulfur compound is a concept including oxygen (O) or sulfur (S) element itself. In a preferred example, oxygen or sulfur in the compound-carbon composite may be present in the carbon- have. For example, by adding oxygen or a sulfur component as an impurity in the course of producing the carbon-based particles, it is possible to obtain a compound-carbon composite which is carbon-based particles containing oxygen or sulfur.

In another preferred embodiment, the oxygen or sulfur compound may be physically or chemically bonded to the surface of the carbon-based particle. At this time, the oxygen or sulfur compound contains a reactive group for bonding with the carbon-based particles.

Examples of the carbon-based particles include graphite such as natural graphite, graphite such as artificial graphite, carbon black, acetylene black, ketjen black, and the like. Examples of the carbon- Carbon black such as black, channel black, furnace black, lamp black, and summer black, or carbon fiber, and these may be used alone or in combination.

In order for the compound-carbon composite material to stably contact with the surface of the lithium-transition metal oxide, the average particle diameter (D50) of the compound-carbon composite material is preferably 50% or less of the average particle diameter (D50) of the lithium-transition metal oxide. And more preferably 10% to 50%.

If the particle diameter of the lithium transition metal oxide is too small, the amount of the binder used increases. If the particle diameter is too large, the tap density is reduced.

The compound-carbon composite material is preferably smaller than the average particle diameter of the lithium transition metal oxide, more preferably 50% or less of the average particle diameter of the lithium transition metal oxide, as described above.

That is, when the size of the compound-carbon composite is too small, the dispersibility may be lowered due to aggregation between the particles, which may make uniform coating difficult. On the contrary, if the size is too large, It may be difficult to exhibit sufficient conductivity.

In order to achieve the effect of the present invention, the lithium transition metal oxide does not necessarily have to be completely coated with the compound-carbon composite. However, if the application area of the compound-carbon composite material is too large, the mobility of lithium ions may be lowered, and if the application area is too small, it may be difficult to exhibit a desired effect. Accordingly, it is preferable that the lithium nickel manganese-based oxide is applied to 20 to 95% of the entire surface of the lithium nickel-based oxide.

The lithium transition metal oxide is not particularly limited as long as it is capable of intercalating and deintercalating lithium ions. For example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) A compound substituted with a metal; 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} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, 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 one preferred example, the lithium transition metal oxide may be a lithium nickel-based oxide having a nickel content of 40% or more in the total transition metal. As described above, when the content of nickel is relatively large as compared with other transition metals, the proportion of the bivalent nickel becomes relatively high. In this case, since the amount of charge capable of moving lithium ions is increased, a high capacity can be exhibited.

However, as the content of Ni is increased, the content of Ni ^{2 +} ions in the lithium nickel oxide increases, and the desorption of oxygen becomes high at high temperature. Therefore, the stability of the crystal structure is low and the specific surface area is high and the impurity content is high. And high temperature safety is low.

However, in the cathode active material according to the present invention, a compound-carbon composite is coated on the surface of the oxide to form a kind of protective film between the surface of the oxide and the electrolytic solution. When applied to a high nickel content lithium nickel oxide, Can be effectively improved and high-capacity characteristics can be sufficiently exhibited.

In a specific example, the lithium nickel based oxide may be a compound represented by the following formula (1).

Li _x Ni _y M _1-y O ₂ (1)

Wherein 0.95? X? 1.05, 0.4? Y? 0.9, and M is at least one selected from the group consisting of Mn, Co, Mg and Al.

In the above formula 1, the lithium content (x) is 0.95 to 1.05, and when the amount of lithium is greater than 1.05, the safety may be lowered during the cycle at a high voltage (U = 4.35 V) . On the other hand, when x < 0.95, a low rate characteristic is exhibited, and the reversible capacity can be reduced.

Also, the content (y) of nickel (Ni) is 0.4 to 0.9 in terms of nickel excess composition relative to manganese and cobalt. When the content of nickel is less than 0.4, it is difficult to expect a high capacity. On the other hand, when the content exceeds 0.9, safety is greatly reduced.

The M may be at least one selected from the group consisting of Mn, Co, Mg, and Al, and may preferably be Mn and Co.

In one preferred example, the lithium nickel oxide represented by Formula 1 may be a lithium nickel-manganese-cobalt oxide represented by Formula 1a below.

Li _x Ni _y Mn _c Co _d O ₂ (1a)

Wherein c + d = 1-y, wherein 0.05? C? 0.4 and 0.1? D? 0.4.

When the content (c) of manganese is less than 0.05, safety is deteriorated. When the content of manganese is larger than 0.4, the amount of charge that can be moved is decreased, and the capacity is decreased.

If the content (d) of the cobalt is in the range of 0.1 to 0.4, b> 0.4, if the content of cobalt is excessively high, the cost of raw materials as a whole increases and the stability of Co ^{4 +} Which is undesirable. On the other hand, when the content of cobalt is excessively low (b < 0.1), it is difficult to achieve sufficient rate characteristics and high powder density at the same time.

In one preferred example, a polymer resin having a melting point of 80 ° C or higher may be further applied to the surface of the lithium transition metal oxide as an electrolyte for a lithium secondary battery and a material inert to the organic solvent.

Since such a polymer resin is inert to an electrolyte solution or an organic solvent, it is not removed during the manufacturing process of the electrode or contained in the battery, so that the polymer resin does not dissolve or decompose into the electrolyte solution. Further, when the internal temperature of the battery reaches a high temperature of 80 DEG C or higher, it melts and sticks to the surface of the active material or flows into the gap between the cathode active materials to lower the lithium ion and electron mobility. So that the electrochemical reaction can be prevented from continuing and the ignition of the battery can be suppressed.

Examples of such a polymer resin include at least one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polystyrene, or a copolymer or blend of two or more thereof, but are not limited thereto.

The melting point of the polymer resin is preferably 80 to 300 캜. If the melting point is less than 80 占 폚, the internal resistance can be increased even in the normal operation state of the battery, thereby deteriorating the battery characteristics. If the melting point is higher than 300 占 폚, it is difficult to exhibit the desired high-temperature safety.

If the content of the polymer resin is excessively high, the internal resistance is increased, and the effect of improving the electrical conductivity and the ionic conductivity due to the application of the compound-carbon composite may not be exhibited.

Also, the compound-carbon composite and the polymer resin may be coated on the surface of the lithium-transition metal oxide in mutually independent phases, or may be coated with the compound in the compound-carbon composite and the polymer resin combined.

The present invention also provides a lithium secondary battery comprising the cathode active material. The lithium secondary battery is composed of, for example, a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte containing a lithium salt, and the like.

The positive electrode is prepared, for example, by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, followed by drying, and if necessary, a filler is further added. The negative electrode is also manufactured by applying and drying the negative electrode material on the negative electrode collector, and if necessary, may further include the above-described components.

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like. Among them, a carbon-based active material, a silicon-based active material, a tin-based active material, or a silicon-carbon based active material is more preferable, and these may be used singly or in combination of two or more.

The separator is an insulating thin film interposed between the anode and the cathode and having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. As such a separation membrane, for example, a sheet or a nonwoven fabric made of olefin-based polymer such as polypropylene which is resistant to chemical and hydrophobic, glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and high molecular weight polyvinyl alcohol.

The conductive material is a component for further improving the conductivity of the electrode active material and may be added in an amount of 1 to 30% by weight based on the total weight of the electrode mixture. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, 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; Carbon fibers such as carbon nanotubes and fullerene; conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey 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.

The viscosity adjusting agent may be added up to 30% by weight based on the total weight of the electrode mixture, so as to control the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the collector may be easy. Examples of such viscosity modifiers include carboxymethylcellulose, polyvinylidene fluoride and the like, but are not limited thereto. In some cases, the above-described solvent may play a role as a viscosity adjusting agent.

The filler is an auxiliary component for suppressing the expansion of the electrode. The filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The coupling agent is an auxiliary component for increasing the adhesive force between the electrode active material and the binder. The coupling agent has two or more functional groups and can be used up to 30% by weight based on the weight of the binder. Such a coupling agent can be obtained by, for example, a method in which one functional group reacts with a hydroxyl group or a carboxyl group on the surface of a silicon, a tin, or a graphite active material to form a chemical bond and the other functional group reacts with a polymeric binder to form a chemical bond Lt; / RTI &gt; Specific examples of the coupling agent include triethoxysilylpropyl tetrasulfide, mercaptopropyl triethoxysilane, aminopropyl triethoxysilane, and chloropropyltriethoxysilane ( chloropropyl triethoxysilane, vinyl triethoxysilane, methacryloxypropyl triethoxysilane, glycidoxypropyl triethoxysilane, isocyanatopropyl triethoxysilane, And silane-based coupling agents such as cyanatopropyl triethoxysilane, but are not limited thereto.

The adhesion promoter may be added in an amount of 10% by weight or less based on the binder, for example, oxalic acid, adipic acid, Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

As the molecular weight modifier, t-dodecylmercaptan, n-dodecylmercaptan, n-octylmercaptan and the like can be used. As the crosslinking agent, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, aryl acrylate, aryl methacrylate, trimethylolpropane triacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, Divinylbenzene and the like can be used.

The current collector in the electrode is a portion where electrons move in the electrochemical reaction of the active material, and an anode current collector and a cathode current collector exist depending on the type of the electrode.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the positive electrode collector may be made of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Surface-treated with carbon, nickel, titanium, silver, or the like may be used.

These current collectors may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, or the like, by forming fine irregularities on the surface of the current collectors to enhance the binding force of the electrode active material.

The lithium-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt.

Examples of the nonaqueous electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, Nitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives , Tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate and the like can be used.

The lithium salt is a material which is soluble in the non-aqueous liquid electrolyte and includes, 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, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have. In some cases, organic solid electrolytes, inorganic solid electrolytes, etc. may be used.

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.

The inorganic solid electrolyte is, 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 and sulfates of Li such as Li ₄ SiO _{4 -} LiI-LiOH and Li ₃ PO _{4 -} Li ₂ S-SiS ₂ can be used.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The lithium secondary battery according to the present invention can be manufactured by a conventional method known in the art. In the lithium secondary battery according to the present invention, the structure of the positive electrode, the negative electrode and the separator is not particularly limited. For example, each of the sheets may be formed into a cylindrical shape by a winding type or a stacking type, Or inserted into a case of a pouch type.

The lithium secondary battery according to the present invention can be preferably used as a power source for a hybrid vehicle, an electric vehicle, and a power tool, which require high rate characteristics and high-temperature safety.

As described above, the cathode active material according to the present invention not only greatly improves ionic conductivity and electrical conductivity, but also can minimize the reactivity with the electrolyte by forming an interface between the surface of the cathode active material and the electrolytic solution, And high temperature safety.

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 (12)

(O) or a composite of a sulfur (S) compound and a carbon-based particle (a 'compound-carbon composite') is coated on the surface of the lithium transition metal oxide, The compound-carbon composite is chemically bonded to the surface of the lithium-transition metal oxide. In the compound-carbon composite, oxygen or sulfur is present in the carbon-based particle itself or physically or chemically bonded to the surface of the carbon- Wherein an electrolyte solution for a lithium secondary battery and a polymeric resin having a melting point of 80 DEG C or higher are additionally coated on the surface of the lithium transition metal oxide as a material inert to the organic solvent. delete The carbonaceous particle according to claim 1, wherein the carbon-based particle is at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, Active material. The positive electrode active material according to claim 1, wherein the compound-carbon composite has an average particle size (D50) of 50% or less of an average particle size (D50) of the lithium transition metal oxide. The positive electrode active material according to claim 1, wherein the carbon-based particles are coated with 20% to 80% of the entire surface of the lithium-transition metal oxide. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is a lithium nickel oxide represented by the following formula (1) Li _x Ni _y M _1-y O ₂ (1) Wherein 0.95? X? 1.05, 0.4? Y? 0.9, and M is at least one selected from the group consisting of Mn, Co, Mg and Al. 7. The positive electrode active material according to claim 6, wherein the lithium nickel oxide is a compound represented by the following formula (1a) Li _x Ni _y Mn _c Co _d O ₂ (1a) Wherein c + d = 1-y, wherein 0.05? C? 0.4 and 0.1? D? 0.4. delete The positive electrode active material according to claim 1, wherein the polymer resin is at least one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polystyrene, or a copolymer or blend of two or more thereof. The positive electrode active material according to claim 1, wherein the compound-carbon composite and the polymer resin are coated on the surface of the lithium transition metal oxide in mutually independent phases. A lithium secondary battery comprising the cathode active material according to any one of claims 1, 3, 7, 9, 10, 12. The lithium secondary battery of claim 11, wherein the secondary battery is used as a power source for a hybrid vehicle, an electric vehicle or a power tool.