KR101925041B1 - Cathode Active Material and Lithium Secondary Battery - Google Patents

Abstract

The present invention is characterized in that Li _a P _b O _c produced by the reaction of a Li by-product derived from the process of synthesizing at least one lithium-transition metal oxide selected from the formula (1) with a substance containing PyOz as a functional group Thereby providing a cathode active material.
Li _{1 + x} M _1-y Ma _y O _{2 -z} A _z (1)
Wherein M, Ma, A, x, y, a, b, c are as defined in claim 1.
In the cathode active material for a secondary battery according to the present invention, Li _a P _b O _c generated by the reaction of Li by-product derived from the synthesis of lithium transition metal oxide with a predetermined ammonium phosphate is applied to the surface of the particles, Can be minimized and swelling of the secondary battery can be prevented.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode active material and a cathode active material,

The present invention relates to a cathode active material and a secondary battery including the same.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

In recent years, there has been a growing interest in environmental issues, and as a result, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, And the like. Although a nickel metal hydride (Ni-MH) secondary battery is mainly used as a power source for such an electric vehicle (EV) and a hybrid electric vehicle (HEV), a lithium secondary battery having a high energy density, a high discharge voltage, Research is actively underway, and some commercialization is in progress.

Particularly, a lithium secondary battery used in an electric automobile must have a high energy density and characteristics capable of exhibiting a large output in a short time, and can be used for more than 10 years under severe conditions in which charging and discharging by a large current are repeated in a short time. It is inevitably required to have safety and long-term life characteristics far superior to those of a small lithium secondary battery.

Lithium-containing cobalt oxide (LiCoO ₂ ) having a layered structure is mainly used as a cathode active material of a lithium ion secondary battery used in a conventional small-sized battery, and LiMnO _{2 having a} layered crystal structure, LiMn _{2 having a} spinel crystal structure ₂ O ₄ , and lithium-containing nickel oxide (LiNiO ₂ ) are being used in some cases.

Among the cathode active materials, LiCoO ₂ is most widely used because it has excellent lifetime characteristics and charge / discharge efficiency, but it has a disadvantage that its structural stability is poor and its cost competitiveness is limited due to resource limitations of cobalt used as a raw material .

Lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have an advantage of being excellent in thermal stability and being inexpensive, but have a problem of small capacity and poor high temperature characteristics.

The LiNiO ₂ cathode active material exhibits a high discharge capacity of the battery, but is difficult to synthesize due to the problem of cation mixing between Li and the transition metal, thereby causing a serious problem in rate characteristics.

A large amount of Li by-products are generated depending on the depth of the cationic mixture, and most of the Li by-products are composed of LiOH and Li ₂ CO ₃ , which causes gelation during the production of the anode paste, This causes gas generation due to the progress of the back-charging and discharging.

Therefore, a need exists for a technique for solving such a problem.

SUMMARY OF THE INVENTION It is an object of the present invention 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 developed a cathode active material for a secondary battery capable of preventing the gelation of the anode paste and the generation of gas in the battery by removing Li by-products as described later .

Thus, produced by the reaction of the material comprising the Li by-products and P _y O _z derived from the synthesis of one or more lithium transition metal oxide is selected from the following general formula (1) is a secondary battery, the positive electrode active material according to the present invention with a functional group Li _a P _b O _c is applied to the surface of the particles.

Li _{1 + x} M _1-y Ma _y O _{2 -z} A _z (1)

In this formula,

M is an element stable to a 6-coordination structure and is at least one element selected from 1-period and 2-period transition metals;

Ma is a metal or non-metal element stable to a 6 coordination structure;

A is at least one member selected from the group consisting of halogen, sulfur, chalcogenide compounds and nitrogen;

-0.3? X? + 0.3; 0? Y <0.7; And 0? Z <0.1;

As described above, in the process of synthesizing the lithium transition metal oxide, the Li by-products generated are not only causing gelation in the process of manufacturing the positive electrode paste, but also cause the generation of gas due to progress of charging / discharging of the battery, It can have a serious impact on safety.

The cathode active material according to the present invention is characterized in that Li _a P _b O _c generated by the reaction of a Li by-product derived from the synthesis of a lithium-transition metal oxide and a substance containing P _y O _z as a functional group is applied The content of the impurities can be reduced, and swelling of the secondary battery can be prevented.

The lithium transition metal oxide may be a composition containing Ni as a transition metal. Specifically, the lithium transition metal oxide may be at least one selected from the following general formula (2).

Li _{1 + x} (Ni _{y '} M' _{1-y '} ) O ₂ (2)

M 'is one or two or more selected from the group consisting of Mn, Co, Cr, Fe, V, and Zr, and -0.3? X? +0.3; And 0.4? Y? 0.9.

In detail, the lithium transition metal oxide may be LiNi _0.8 Mn _0.1 Co _0.1 O ₂ .

Although the lithium transition metal oxide containing Ni has an advantage that it can have a high discharge capacity, the ion size of Ni ²⁺ is similar to that of Li ⁺ , so that the cation mixing occurs well and a lot of Li byproducts are produced in the manufacturing process .

Therefore, the cathode active material according to the present invention is converted into a stable material by the reaction of a substance containing P _y O _z as a functional group, and is applied to the surface of the Li by-product generated in the manufacturing process, .

The reaction of the Li by-product and the substance containing P _y O _z as a functional group can be represented by, for example, the following reaction formula a.

aLi _X + b (P _y O _z ) → c Li _a P _b O _c (a)

In the above reaction formula (a), x is 1 to 5, y is 1 to 2, c is 1 to 7, and a, b, and c are any integers or a prime.

In this reaction, the amount of the substance containing the P _y O _z as a functional group may be 0.05 to 10% by weight based on the total weight of the lithium transition metal oxide. If the amount of the substance containing P _y O _z as a functional group is excessively large, it may interfere with the occlusion and desorption of lithium, and if it is too small, it is not possible to sufficiently remove Li by-products. Specifically, the amount of the substance containing the P _y O _z as a functional group may be 0.1 to 5 wt% based on the total weight of the lithium transition metal oxide.

Materials, including the P _y O _z with a functional group are X (PO ₄₎ q (where X is _{Fe, LiFe, (NH 4)} H 2, (NH 4) 2 H, (NH 4) selected from the group consisting of: ₃ and one or more of which, 0≤q≤3 a) may be, specifically, mono-ammonium phosphate _{((NH 4) H 2 PO} 4), dimethyl ammonium phosphate _{((NH 4) 2 HPO 4} ), or tri-ammonium phosphate It may be _{((NH 4) 3 PO 4} ) may be, more particularly, di-ammonium phosphate _{((NH 4) 2 HPO 4} ).

The Li _a P _b O _c produced by the above reaction may be Li ₄ P ₂ O ₇ or LiPO _{3 in} detail.

The Li _a P _b O _c generated by the above reaction may be locally applied to 80% or less, specifically 60% or less, based on the total surface area of the lithium transition metal oxide particles.

As described above, the Li by-product is generated by cationic mixing between Li and a transition metal in the process of synthesizing a lithium transition metal oxide, and most can be LiOH and Li ₂ CO ₃ .

The amount of residual Li by-products not participating in the reaction depends on the amount of the substance containing the P _y O _z as the functional group, but may be 2% by weight or less based on the total weight of the lithium transition metal oxide.

The pH of the cathode active material may vary from 10 to 12 depending on the amount of Li by-products that do not participate in the reaction and remain.

Also, in the cathode active material, the reaction of the Li by-product and the material containing P _y O _z as a functional group may occur at a temperature of 100 ° C to 700 ° C.

A positive electrode mixture prepared by adding a conductive material and a binder to the positive electrode active material may be prepared.

The positive electrode mixture may contain a predetermined solvent such as water or NMP to form a slurry. The slurry may be coated on the positive electrode current collector, followed by drying and rolling to produce a positive electrode. As described above, the cathode active material according to the present invention is characterized in that Li by-products are removed and gelation can be prevented during the production of the slurry.

The positive electrode is prepared, for example, by applying a slurry of a mixture of a positive electrode active material, a conductive material and a binder according to the present invention on a positive electrode current collector, followed by drying. If necessary, the positive electrode active material, The mixture (electrode mixture) of the binder and the like may further contain at least one substance selected from the group consisting of a viscosity adjusting agent and a filler.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material is a component for further improving the conductivity of the electrode active material and may be added in an amount of 0.01 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 binder is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. Examples of such binders 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 the like.

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 optionally used as 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 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 thus prepared positive electrode can be used for manufacturing a lithium secondary battery together with a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode is manufactured by coating a negative electrode material on a negative electrode collector and drying the same, and if necessary, may further include components such as a conductive material and a binder as described above.

The negative electrode 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. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

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 separation membrane is interposed between the anode and the cathode, and 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 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.

The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

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.

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.

Examples of the inorganic solid electrolyte include 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 _a P _b O _c -Li ₂ S-SiS ₂ can 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, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving charge / discharge characteristics, flame retardancy, etc., non-aqueous electrolytes may be used in the form of, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. 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 present invention also provides a battery module using the lithium secondary battery as a unit cell, and a battery pack including the battery module.

Therefore, the secondary battery according to the present invention can be suitably used as a power source for a middle- or large-sized device which is required not only for a battery cell used as a power source for a small device but also for a high-temperature safety, a long cycle characteristic and a high rate characteristic.

Preferred examples of the above medium to large devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart, and the like, but the present invention is not limited thereto.

As described above, in the cathode active material for a secondary battery according to the present invention, Li _a P _b O _c generated by the reaction of a Li by-product derived from the synthesis of a lithium-transition metal oxide with a predetermined ammonium phosphate, So that the content of impurities can be minimized and swelling of the secondary battery can be prevented.

Hereinafter, the present invention will be described in more detail with reference to some embodiments thereof, but the scope of the present invention is not limited thereto.

&Lt; Example 1 >

LiNiO.₈Mn_0.1Co_0.1O₂in 0.4% by weight based on the total weight of the lithium transition metal oxide and the diammonium phosphate represented by the lithium transition metal oxide were mixed and heat-treated at 300 占 Thereby preparing a cathode active material.

&Lt; Example 2 >

The cathode active material was prepared in the same manner as in Example 1, except that the anode active material was heat-treated at 500 ° C.

&Lt; Example 3 >

A cathode active material was prepared in the same manner as in Example 1, except that monoammonium phosphate was used.

<Example 4>

A cathode active material was prepared in the same manner as in Example 1 except that monoammonium phosphate was used for heat treatment at 500 ° C

&Lt; Example 5 >

A cathode active material was prepared in the same manner as in Example 1, except that triammonium phosphate was used.

&Lt; Example 6 >

A cathode active material was prepared in the same manner as in Example 1, except that triammonium phosphate was used for heat treatment at 500 ° C.

&Lt; Example 7 >

A cathode active material was prepared in the same manner as in Example 1, except that di-ammonium phosphate was mixed in an amount of 0.6% by weight based on the total weight of the lithium-transition metal oxide.

&Lt; Example 8 >

A cathode active material was prepared in the same manner as in Example 1, except that di-ammonium phosphate was mixed in an amount of 0.8 wt% based on the total weight of the lithium-transition metal oxide.

&Lt; Comparative Example 1 &

A cathode active material was prepared in the same manner as in Example 1, except that the monoammonium phosphate was not mixed.

<Experimental Example 1>

The pH and the like of the cathode active material prepared according to the above Examples and Comparative Examples were measured and shown in Tables 1 and 2 below.

Temperature
(° C) Mixing
Time
(min) Diammonium phophate
input
(wt%) D50
(탆) ΔPSD pH Li ₂ CO ₃
(wt%) LiOH
(wt%) Ex Li
wt% Example 1 300 60 0.4 11.2 0.39 11.4 0.247 0.125 0.372 Example 7 0.6 11.23 0.38 11.48 0.218 0.158 0.376 Example 8 0.8 11.38 0.21 11.49 0.216 0.161 0.377 Example 2 500 120 0.4 11.16 0.2 11.65 0.079 0.253 0.332 Comparative Example 1 300 60 - 10.98 0.14 11.69 0.257 0.249 0.506

According to Table 1, the high-content Ni-based cathode active material LiNiO. ₈ Mn _0.1 Co _0.1 O ₂ , the surface byproducts of Examples 1 and 2, which were surface-treated by the above method, are reduced.

Temperature
(° C) Mixing
Time
(min) Ammonium phophate Input (wt%) moisture
content
(ppm) charge
(mAh / g) Discharge
(mAh / g) 1 ^st efficiency
% C-rate
% Example 1 300 60 0.4 245 215.3 191.2 88.8 88.3 Example 7 0.6 300 215.6 191.3 88.8 88.4 Example 8 0.8 371 215.3 191.2 88.8 88.1 Example 2 500 120 0.4 207 216.1 195.3 90.4 87.8 Comparative Example 1 300 60 - 253 215.9 194.0 89.9 88.7

According to Table 2 above, the high-content Ni-based cathode active material LiNiO. _{As a} result of the coin cell test using ₈ Mn _0.1 Co _0.1 O ₂ , the cells of the surface treated by applying the above process showed capacity and rate performance equal to those of the battery of the comparative example, even though Ammonium phophate was added Able to know.

<Experimental Example 2>

Ammonium phosphate irradiation on the surface of the cathode active material according to Examples 1 to 7 is shown in Table 3 below.

Example XRD results after 300 ° heat treatment XRD results after 500 ° heat treatment Examples 3 and 4 Li ₂ CO ₃
Li ₃ PO ₄
Li ₄ P ₂ O ₇
LiPO ₃ Li ₂ CO ₃
Li ₃ PO ₄
Li ₄ P ₂ O ₇
LiPO ₃ Examples 1, 2, 7 and 8 Li ₂ CO ₃
-
Li ₄ P ₂ O ₇
- Li ₂ CO ₃
-
Li ₄ P ₂ O ₇
LiPO ₃ Examples 5 and 6 Li ₂ CO ₃
Li ₃ PO ₄
Li ₄ P ₂ O ₇
- Li ₂ CO ₃
Li ₃ PO ₄
Li ₄ P ₂ O ₇
LiPO ₃

According to the above Table 3, as a result of the ammonium phosphate treatment test using the high-Ni-based cathode active material, the XRD of the surfaces treated with the above process was Li _a P _b O _c (x is 1-5, y is 1- 2, and Z is 1-7). In particular, it can be confirmed that Li ₃ PO ₄ was not detected as an impurity in the case of Examples 1, 2, 7 and 8 in which the treatment with diammonium phos- tate was carried out.

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 (20)

Li _a P _b O _c generated by the reaction of a Li by-product derived from the process of synthesizing at least one lithium-transition metal oxide selected from the following formula (1) with a substance containing P _y O _z as a functional group is applied to the surface of the particles Wherein the positive electrode active material is a positive electrode active material,
In this reaction, the amount of the substance containing the P _y O _z as a functional group is 0.05 to 10% by weight based on the total weight of the lithium transition metal oxide,
Wherein the material containing P _y O _z as a functional group is a diammonium phosphate ((NH ₄ ) ₂ HPO ₄ ), a cathode active material:
Li _{1 + x} M _1-y Ma _y O _{2 -z} A _z (1)
In this formula,
M is an element stable to a 6-coordination structure and is at least one element selected from 1-period and 2-period transition metals;
Ma is a metal or non-metal element stable to a 6 coordination structure;
A is at least one member selected from the group consisting of halogen, sulfur, chalcogenide compounds and nitrogen;
-0.3? X? + 0.3; 0? Y <0.7; And 0? Z <0.1;
1? A? 5; 1? B? 2; And 1? C? 7. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is at least one selected from the group consisting of the following formula (2)
Li _{1 + x} (Ni _{y '} M' _{1-y '} ) O ₂ (2)
M 'is one or two or more selected from the group consisting of Mn, Co, Cr, Fe, V, and Zr, and -0.3? X? +0.3; And 0.4? Y? 0.9. The lithium secondary battery according to claim 1, wherein the lithium transition metal oxide is LiNiO. ₈ Mn _0.1 Co _0.1 O ₂ . delete The positive electrode active material according to claim 1, wherein the amount of the material containing P _y O _z as a functional group is 0.1 to 5 wt% based on the total weight of the lithium transition metal oxide. The method of claim 1, wherein the material comprising P _y O _z as a functional group is X (PO ₄ ) q wherein X is Fe, LiFe, (NH ₄ ) H ₂ , (NH ₄ ) ₂ H, (NH ₄ ) ₃ , and 0 &lt; / = q &lt; / = 3). delete delete The positive electrode active material according to claim 1, wherein Li _a P _b O _c is Li ₄ P ₂ O ₇ or LiPO ₃ . The positive electrode active material according to claim 1, wherein the Li _a P _b O _c is applied in an amount of 80% or less based on the total surface area of the lithium transition metal oxide particles. The positive electrode active material according to claim 1, wherein the Li by-product is LiOH and Li ₂ CO ₃ . The positive electrode active material according to claim 1, wherein the amount of Li by-products remaining after the reaction is 2% by weight or less based on the total weight of the lithium transition metal oxide. The positive electrode active material according to claim 1, wherein the reaction of the Li by-product and the material containing P _y O _z as a functional group occurs at a temperature of 100 ° C to 700 ° C. A positive electrode for a secondary battery, comprising the positive electrode active material according to claim 1. A secondary battery comprising a positive electrode according to claim 14. The secondary battery according to claim 15, wherein the battery is a lithium secondary battery. The battery module according to claim 15, wherein the secondary battery is used as a unit battery. A battery pack comprising the battery module according to claim 17. The battery pack according to claim 18, wherein the battery pack is used as a power source for a middle- or large-sized device. 20. The battery pack of claim 19, wherein the middle- or large-sized device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.