WO2019083157A1 - Positive electrode active material comprising lithium-rich lithium manganese oxide having formed thereon coating layer comprising lithium-deficient transition metal oxide, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention provides a positive electrode active material comprising lithium-rich lithium manganese oxide, and a method for preparing same, the lithium-rich lithium manganese oxide being represented by chemical formula (1), Li1+aNixCoyMnzMvO2-bAb (1), wherein: 0<a≤0.2, 0<x≤0.4, 0<y≤0.4, 0.5≤z≤0.9, 0≤v≤0.2, a+x+y+z+v=1, 0≤b≤0.5; M is one or more element selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga, In, Ru, Nb and Sn; A is one or more element selected from the group consisting of P, N, F, S and Cl; and a coating layer is formed on the surface of the lithium-rich lithium manganese oxide, the coating layer comprising a lithium-deficient transition metal oxide that is deficient in lithium with lithium being included at a mole ratio of less than 1 relative to the transition metal, and the amount of the coating layer being 1-10 weight% with respect to the total weight% of the positive electrode active material.

Description

 Title of the Invention

 A positive electrode active material comprising a lithium-excess lithium manganese-based oxide having a coating layer containing a lithium-deficient transition metal oxide formed thereon and a positive electrode for a lithium secondary battery comprising the same

 TECHNICAL FIELD

Cross-reference with related application (s)

 This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0140282, filed on October 26, 2017, and Korean Patent Application No. 10-2018-0096965, filed on August 20, 2018, The entire contents of which are incorporated herein by reference.

 The present invention relates to a positive electrode active material comprising a lithium-excess lithium manganese-based oxide having a coating layer containing a lithium-deficient transition metal oxide formed thereon, and a positive electrode for a lithium secondary battery comprising the same.

 BACKGROUND ART [0002]

 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 addition, as interest in environmental issues has increased recently, studies on electric vehicles and hybrid electric vehicles capable of replacing fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, have. Although a nickel metal hydride secondary battery is mainly used as a power source for such electric vehicles and hybrid electric vehicles, researches using a lithium secondary battery having a high energy density and a discharge voltage, a long cycle life and a low self-discharge rate are actively conducted And is in the process of commercialization.

As a negative electrode active material of such a lithium secondary battery, a carbon material is mainly used, and the use of lithium metal, a sulfur compound and the like are also considered. Further, the positive electrode active material to mainly lithium-containing cobalt oxide (LiCo0 ₂₎ is used, the addition of LiMn0 _2, the spinel crystal structure of the layered crystal structure of LiMn ₂ 0 _4, etc. Lyrium containing manganese oxide, Lyrium nickel oxide (LiNi0 of ₂ ) is also considered. One of the positive electrode active material LiCo0 ₂ is life ^"properties and layer-discharge efficiency, but superior to the most widely used, the structural stability is poor, because it is expensive due to resource limitations of the cobalt used as the raw material have the disadvantage that a limit on the price competitiveness And there is a limit to mass use as a power source for fields such as electric vehicles.

The LiNiO ₂ cathode active material exhibits a relatively low cost and a high discharge capacity, but exhibits a rapid phase transition of the crystal structure in accordance with the volume change accompanying the layer discharge cycle, and the safety is significantly lowered when exposed to air and moisture There is a problem.

In addition, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have an advantage that they are excellent in thermal stability and low in cost, but have a small capacity, poor cycle characteristics, and poor high temperature characteristics.

 Therefore, attempts have been made to use an excess of lithium oxide having a high capacity of 270 mAh / g or more under a high voltage of 4.5 V or higher because the content of lyrium in the lithium transition metal oxide containing a high Mn content is higher than that of the transition metal .

 The oxide having an excess lithium composition has a low compositional ratio and has a composition limit, so that the primary particles are made small and the BET of the secondary particles is made large to control the structure in a direction to improve the rate characteristic. However, such structural control has a problem that the surface is rough and the rolling density is lowered.

 Furthermore, since the oxide of the excess lithium composition leaks to the outside of the active material structure in addition to lithium in addition to lithium at the time of high voltage activation to utilize excess lyrium, the active material structure collapses and a voltage drop phenomenon occurs thereby promoting degeneration of the battery sal , Resistance due to electrolytic decomposition due to high voltage driving, gas generation, and the like.

In order to solve this problem, in the past, the surface of such a cathode active material was coated with a metal oxide to enhance the surface stability. In this case, the electrical conductivity and the ion conductivity were lowered by the coated metal oxide, But also the loss of capacity due to the reduction of the mass of the active material due to the weight of the coating layer.

 Therefore, there is a high need for a cathode active material technology that has excellent battery cell performance while solving the problem of the oxide of the excess lithium excess composition.

 DETAILED DESCRIPTION OF THE INVENTION

 [Technical 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 found that when the molar ratio of lithium to transition metal is 1 (mole ratio) to the surface of a lithium-excess lithium manganese-based oxide And a lithium-deficient transition metal oxide having a lithium deficiency state is formed on the surface of the positive electrode active material, the present invention has been accomplished.

 [Technical Solution]

 Therefore, the positive electrode active material according to the present invention,

 1. A cathode active material comprising lithium-excess lithium manganese-based oxide, wherein the lithium-excess lithium manganese-based oxide is represented by the following chemical formula (1)

_{Li 1 + a Ni x Co y} Mn z M v 0 2- bA b (1)

 0 < v < 0.2, a + x + y + z + v = 1, 0 < b <0.5;

M is a group consisting of Al, Zr, Zn, Ti, Mg, Ga, In, Ru,

One or more elements selected;

 A is one or more elements selected from the group consisting of P, N, F, S and Cl;

 Wherein a coating layer containing a lithium-deficient transition metal oxide having a lithium molar ratio of less than 1 with respect to transition metals and lacking lithium is formed on the surface of the lithium-excess manganese-based oxide,

The amount of the coating layer is characterized in that 1 part by weight _^0/0 to 10 parts by weight _^0/0, based on the total weight of the positive electrode active material. Specifically, 0 &lt; x &lt; 0.2, 0 &lt; y &lt; 0.2, 0.6 < z < 0.9, 0 < v < 0.1 in order to exhibit a higher high capacity under a high voltage.

 Generally, as described above, an active material having an Mn content of 50 mol% or more as the lithium-excess lithium manganese-based oxide has been actively developed as a high-voltage, high-capacity material for realizing a high energy density. However, since the active material is a negative electrode according to high voltage driving, the resistance of the positive electrode active material increases, the resistance due to electrolyte decomposition increases, and the gas is generated, thereby further promoting degradation of the battery electrolyte. Do.

In this connection, other active materials other than the above-mentioned composition have the above-mentioned problems at the time of driving at a high voltage, and attempts have been made to introduce a coating layer of a metal oxide such as Al ₂ O ₃ and WO ₃ . However, the cathode active material according to the present invention has an additional problem that lithium manganese oxide having Mn of 50 mol% or more is limited in low rolling density and rate characteristics in the realization of energy density. By coating the above metal oxide Rather, the rate characteristics are further deteriorated, and the problem of the cell performance other than the surface protection still remains.

 In addition, the active material according to the present invention is essential for solving the problem of low rolling density to realize high energy density. However, when a coating layer of a lithium transition metal oxide is formed on a cathode active material in general, although the effect of improving the performance of other battery cells can be obtained, the rolling density is lowered and a limited active material However, such attempts have been difficult in lithium-excess lithium manganese-based oxides, which are difficult to obtain a desired rolling density as described above.

 Further, when a lithium metal oxide composed of elements other than Ni, Mn, and Co is coated on the cathode active material, there is a problem that the capacity is lowered due to the decrease of the active material due to the increase in the weight of the coating layer. Is coated with a general lithium transition metal oxide, the movement of lithium is not smooth and the layer discharge rate characteristics are deteriorated.

The inventors of the present application have conducted intensive research and have found that a lithium-deficient transition metal oxide having a molar ratio of lithium to transition metal of less than 1 on the surface of the lithium-excess lithium manganese oxide according to the present invention The coating layer It is possible to realize a high energy density by solving the problem of lowering the rolling density and the rate characteristic as characteristic defects in the lithium-excess lithium manganese-based oxide as well as improving the surface protection property achieved by the coating And reached the present invention.

 In other words, unlike other active materials, in which the rolling density is rather lowered by the coating of the lithium transition metal oxide, the lithium manganese oxide having a lithium excess according to the present invention is improved in rolling density by introducing the coating layer in the form of lithium transition metal oxide And at the same time, lithium was depleted, and the rate characteristics were further improved.

 Accordingly, the lithium-deficient transition metal oxide formed on the surface of the lithium-excess lithium manganese-based oxide according to the present invention may be a substance represented by the following chemical formula (2).

Li _a 'Me0 ₂ (2)

 Where 0 < a &lt; l,

Me may be two or more elements selected from the group consisting of Ni, Co, and Mn, and specifically Me = Ni _x 'Co _y ' Mn _z ^, where 0 <x ' 0 < y < 0.7 and 0.2 &lt; z <'&Lt; 0.6.

 When the coating layer contains Ni, Mn, and Co, the coating layer can act as an active material. As a result, the weight of the active material decreases substantially due to the increase in the weight of the coating layer, In the case of this deficiency, as described above, there is an effect that the movement of lithium is smooth and the rate characteristic is improved, and it is preferable to have such a composition. Further, when the coating layer contains both Ni, Mn and Co, it is more preferable to improve the structural stability and thermal stability as compared with the case where each composition is present singly.

The molar ratio of lithium to transition metal in the lithium-deficient transition metal oxide may be 0.5 to 0.9, more specifically 0.7 to 0.9. When the molar ratio of lithium is decreased to less than 5, the metal oxide (Me _s O _t ) structure without Li is formed, which may interfere with the movement of lithium ions, which is not preferable. If satisfied, it exhibits the best rate characteristic.

At this time, the amount of the coating layer may be based on the total weight of the positive electrode active material, 1 parts by weight ⁰ /. May be to 10% by weight, particularly 3% to 7 Increased _^0/0.

 In addition, the thickness of the coating layer may be 30 nm to 200 nm, and more specifically, 30 nm to 150 nm. This can be measured based on TEM photographs.

Out of the range, if the content of the coating layer 10 parts by weight _^0/0, a thickness exceeding 200 nm has rather, the coating acts as a resistor and may receive the increase and rate properties reduce the reduced capacity, the content is 1 wt. %. If the thickness is less than 30 nm and too low, the surface protective property of the positive electrode active material can not be exhibited, and the effect of improving the rolling density is also deteriorated.

 Since the lithium-excess lithium manganese-based oxide generally has an average particle diameter (D50) of 1/50 to 50 / m, the thickness of the coating layer accounts for 0.06 to 20% of the particle diameter of lithium-excess lithium manganese-based oxide.

The average particle diameter (D ₅₀ ) is defined as the particle diameter at the 50% reference of the particle diameter distribution, and can be measured using, for example, a laser diffraction method.

 Further, the present invention provides a method for producing the above-mentioned cathode active material,

 (i) a process in which a lithium-deficient transition metal oxide having lithium-deficient lithium manganese-based oxide and a lithium-deficient transition metal oxide contained in a molar ratio of lithium to transition metal is less than 1; And

 (ii) heat treating the mixture of step (i);

 / RTI &gt;

The lithium-deficient transition metal oxide is lithium manganese oxide and lithium of the lithium-excess-deficient, based on the total weight of transition metal oxide 1 ⁰ wt / wt to 10 to _^0/0 May be included to include.

At this time, the lithium-deficient transition metal oxide for forming the desired amount of the coating layer has a weight ratio of 3: ⁰ to 7: 7 based on the total weight of lithium excess lithium manganese oxide and lithium- Weight ⁰ /.

The ^{intermingling} of the process (i) is not limited to a known method as a known technique, but in detail, it may be a dry coagulation method, and more specifically, it may be achieved by a ball mill interchange.

 Here, the average particle diameter (D50) of the lyrium-deficient transition metal oxide may be 0.05 to 1.

 Therefore, the lithium-deficient transition metal oxide can be first attached to the surface of the lithium-excess lithium manganese-based oxide in the form of particles by the above-mentioned coalescence.

 The thus formed impurities can be bonded firmly in the form of particles by heat treatment or the lithium-deficient transition metal oxide can be changed into a film form, thereby allowing space between lithium-excess lithium manganese-based oxide particles to be spun . At this time, the heat treatment may be performed at 600 to 1100 degrees Celsius and may be performed for 5 to 12 hours.

 If the heat treatment temperature is too low, the layer may not be formed as a coating layer. If the heat treatment temperature is too high, the excess lithium manganese oxide constituting the cathode active material particles and the lithium-deficient transition metal The physical and chemical properties of the cathode active material can be changed such that the oxide is totally repelled and dissolved, which is undesirable.

 Alternatively, the method for producing the cathode active material according to the present invention comprises:

 (a) coating a surface of a lithium-excess lithium manganese-based oxide in a particle state with a transition metal precursor;

 (b) further adding a lithium source material to the lithium manganese oxide coated with the transition metal precursor, thereby complicating the process; And

 (c) heat treating the impurities of step (b);

/ RTI &gt;

The amount of the lithium source material injected in the process (b) depends on the amount of the transition metal precursor And the molar ratio of lithium to total moles of transition metal is less than 1.

 In this case, the transition metal precursor and the lithium source may be introduced such that the coating layer in the resulting structure satisfies the above-mentioned content.

 The transition metal precursor coated on the surface of the lithium manganese-based oxide may be at least two elements selected from the group consisting of Ni, Mn, and Co, specifically, a hydroxide including all of the above materials.

 This may be achieved by coprecipitation in which a surface of the lithium manganese oxide is coprecipitated with transition metal sources in a solvent, or a transition metal precursor prepared by coprecipitation may be formed by a dry process such as a ball milling process.

 Similarly, the intercalation of the lithium source material in process (b) may also be performed by a wet or dry process so as to be continuous with process (a).

In this case, the lithium source material is Li ₂ C0 _3, LiOH, LiN0 _3, CH ₃ one or more may be, specifically, the lithium source material is selected from the group consisting of COOLi and Li ₂ (COO) ₂ is, Li ₂ C0 ₃ or LiOH.

 The heat treatment may be performed at 600 to 1100 degrees Celsius, and may be performed for 5 to 12 hours, similarly to the first manufacturing method.

 The present invention also provides a positive electrode in which a positive electrode mixture containing the positive electrode active material is formed on a current collector.

 The positive electrode material mixture may further include a conductive material and a binder in addition to the positive electrode active material.

 Specifically, the positive electrode can be produced, for example, by applying, drying and rolling a positive electrode slurry in which a positive electrode active material, a conductive material and a binder are mixed in a positive electrode current collector.

The cathode current collector is generally manufactured to a thickness of 3 to 500 micrometers and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium , And a surface treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel can be used. Specifically, aluminum can be used. The current collector has a fine It is possible to increase the adhesive force of the cathode active material by forming unevenness, 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 cathode active material may be, for example, a layered compound such as lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals in addition to the cathode active material particle; Lithium manganese oxides such as Li _{1 + x} Mn _2-x 0 ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-x M x 0 2} ( where, M = Co, Μη, and .ΑΙ, Cu, Fe, Mg, B or Ga, x = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; The formula LiMn ₂ . _x M _x 0 ₂ (where, M = Co, and Ni, Fe, Cr, Zn or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ M0 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, but is not limited thereto. Of course, may be configured with only the positive electrode active material according to the present invention, a positive electrode active material according to the invention may contain at least 80 parts by weight _^0/0 above.

 The conductive material is usually added in an amount of 0.1 to 30% by weight based on the total weight of the charge including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, for example, natural graphite or artificial rhizome; 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 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 a component that assists in binding of the active material to the conductive material and bonding to the current collector, and is usually added in an amount of 0.1 to 30% by weight based on the entire amount of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, cellulose (CMC), starch, hydroxypropyl sal, rosewood, , Polypropylene, ethylene-propylene-diene ter Polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

 The positive electrode may be used as a positive electrode for a lithium secondary battery, and the lithium secondary battery is composed of the positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

 Hereinafter, other configurations of the lithium secondary battery will be described.

 The negative electrode is fabricated by applying a negative electrode active material on the negative electrode collector and drying the negative electrode active material. Optionally, the negative electrode may further include components included in the positive electrode described above.

The negative electrode collector is generally made to have a thickness of 3 to 500 micrometers. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, the anode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel 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 such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤l} ), Li x WO 2 (0 <x <l), 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 and Group 3 elements of the periodic table, Halogen; 0 <x <1; l <y <3; 1 <zeta <8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{4 SnO, Sn0 2, PbO,} Pb0 2, Pb 2 0 3, Pb 3 0 4, Sb 2 0 3, Sb 2 0 4, Sb 2 0 5, GeO, Ge0 2, Bi 2 0 3, Bi 2 0, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

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 / m, and the thickness is generally 5 to 300 plates. Examples of such a separator include a refractory polymer such as polypropylene, which is resistant to chemicals 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 the electrolyte, The electrolyte may also serve as a separator.

 The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt. The non-aqueous electrolyte includes non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like.

 Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, gamma -butyrolactone, 1,2-dimeroxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, But are not limited to, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimeroxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3- Ethers, methyl pyrophonate, ethyl propionate and the like can be used as the organic solvent.

 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, Lil, 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 Si0 ₄ -LiI-LiOH and Li ₃ PO ₄ -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, Lil, LiC10 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 S0 3, LiCF 3 C0 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 S0 3 Li, CF 3 S0 3 Li, (CF 3 S0 2) 2 NLi, chlorocarbonate borane lithium, lower aliphatic acid Lyrium, _tetraphenyl borate Lyrium, and imide have.

For the purpose of improving the layer discharge characteristics and the flame retardancy, the nonaqueous electrolyte solution may contain at least one selected from the group consisting of pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyridine, 2-methoxyethanol, It is possible. In some cases, in order to impart nonflammability, carbon tetrachloride, ethylene trifluoride , And may further contain a carbon dioxide gas to improve the high-temperature storage characteristics, and may further include FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), and the like.

 BRIEF DESCRIPTION OF THE DRAWINGS

 1 is an SEM photograph of a cathode active material according to Example 1;

 2 is an SEM photograph of the cathode active material according to Comparative Example 1;

 3 is a comparative graph of the rolling density according to Experimental Example 1;

 4 and 5 are graphs comparing rolling densities according to the reference example.

 DETAILED DESCRIPTION OF THE INVENTION

 Hereinafter, the present invention will be described with reference to embodiments thereof, but it should be understood that the scope of the present invention is not limited thereto. &Lt; Preparation Example 1 &

 A precursor was synthesized such that the ratio of Ni, Mn, and Co was in a molar ratio of 20: 20: 60,

Li ₂ C0 ₃ and Li: (Ni + Mn + Co ) = L28: the first firing temperature to a common combined banung back so that the molar ratio (fiimace) at 940 ^° C for 10 hours, Li _U4 Nio. ₁₇ Co ₀ . ₁₇ was prepared Mno.5 ₂ 0 _2. &Lt; Preparation Example 2 &

The precursor was synthesized so that the ratio of Ni, Co, and Mn was 12: 12: 76. Then, the precursor was mixed so that the molar ratio of Li ₂ CO ₃ and Li: (Ni + Mn + Co) = 1.3: (fiimace) was calcined at 940 ^° C for 10 hours to prepare LiusNiojCOojMn ^ Ch. &Lt; Preparation Example 3 &

Precursors were synthesized so that the molar ratio of Ni, Co, and Mn was 11: 11: 78, and the molar ratio of Li ₂ CO ₃ to Li: (Ni + Mn + Co) = 1.2: The temperature of the fornace was calcined at 940 ^° C for 10 hours to obtain LiuNiojCOcnMno _. ^. &Lt; Example 1 > Lij. _H Nio.nCoo.nMno.szO, and Li ₀ . ₉ Nio. ₃ Co ₀ . ₂ Mno. ₅ 0 ₂ were mixed at a weight ratio of 96: 4, and the mixture was fired in a furnace at 800 ° C for 10 hours to form a coating layer having a thickness of 60 nm to prepare a cathode active material.

 SEM photographs of the synthesized cathode active material are shown in FIG.

 Referring to FIG. 1, the cathode active material according to Example 1 is shown in Comparative Example

1, it can be confirmed that the space between the particles is filled with the cathode active material. As a result, the roughness of the surface of the active material is greatly reduced as the space between the particles is filled. Thus, it can be seen that the positive electrode active material according to Example 1 forms a smooth surface compared to the positive electrode active material according to Comparative Example 1. &Lt; Example 2 >

Li _{u 4} Ni ₀ . ₁₇ Coo. ₁ 7Mno _.52 0 ₂ and Li ₀ . ₉ Nio. ₃ Coo. ₂ Mno _.5 0 ₂ in a weight ratio of 92: 8 to form a coating layer having a thickness of 120 nm. The cathode active material was prepared in the same manner as in Example 1, except that a coating layer having a thickness of 120 nm was formed.

&Lt; Example 3 >

 The Liu5Mo.iCOojMno.65O2 prepared in Preparation Example 2 and

Li ₀ . ₉ Ni ₃ Co ₀ . ₂ Mno _.5 0 ₂ were mixed in a weight ratio of 96: 4 to prepare a cathode active material.

<Example 4>

 A cathode active material was prepared in the same manner as in Example 1, except that LiuNio.iCOojMno.7O2 and Lio.9Nio.3Coo.2Mno.5O2 prepared in Preparation Example 3 were mixed in a ball mill to a weight ratio of 96: 4.

&Lt; Comparative Example 1 &

 Liu4Nio.nCoo.nMno.52O2 was prepared as a cathode active material.

 The synthesized cathode active material and SEM photograph are shown in FIG.

&Lt; Comparative Example 2 & Liu4Nio.nCoo.nMno.52O2 and Li _{0. 9} Ni ₀ . ₃ Co ₂ Mn ₀ . ₅ O ₂ in a weight ratio of 88:12 to form a coating layer having a thickness of 180 nm. The cathode active material was prepared in the same manner as in Example 1 except that a coating layer having a thickness of 180 nm was formed. &Lt; Comparative Example 3 &

Liu4Nio _. nCoo.nMno.52O2 and LiNio. ₆ Co _0.4 O ₂ in a weight ratio of?: 96: 4 to form a coating layer having a thickness of 60 nm. A cathode active material was prepared in the same manner as in Example 1, except that a coating layer having a thickness of 60 nm was formed. &Lt; Comparative Example 4 &

Liu4 io _. nCoo.17Mno.52O2 and Li ₂ CoO ₀ to ₉ in the weight ratio 96: The combined so that the common ball mill 4, to prepare a cathode active material and in the same manner as in Example 1 except for forming a coating layer of a thickness of 60 nm. <Experimental Example 1>

 Powder rolling densities of the respective cathode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured, and the results are shown in FIG.

 Referring to FIG. 3, when the coating layer is formed according to the present invention, the rolling density is improved, and it is confirmed that the rolling density begins to decrease again for a coating amount exceeding a certain amount. This indicates that there is an optimum condition for improving the rolling density in the coating content, and it is expected that the rolling density will start to be lowered when a coating amount exceeding a certain amount is applied. &Lt; Reference Example 1 &

LiNio.33Coo.33Mno.35O2 and Lio _.9 Nio. ₃ Co ₀ . ₂ Mno. ₅ 0 ₂ were mixed in a weight ratio of 96: 4 to prepare a cathode active material in the same manner as in Example 1.

&Lt; Reference Example 2 &

LiNi ₀ . ₅ Coo. ₂ Mn ₀ .30 ₂ and Li _0.9 Ni _0.3 Co _0.2 Mn _0.5 O ₂ in a weight ratio of 96: 4 The cathode active material was prepared in the same manner as in Example 1 except that the ball mill was used.

&Lt; Reference Experimental Example &

When using only Reference Example _{1 1 ^ 1 0.33) 0.3 ^} ¾33 0 2 of a cathode active material, and a change in the rolling density, in the case of using as a positive electrode active material coating layer formed in the Reference Example 1, Reference Example 2 of LiNio.5Coo. To confirm the change in the rolling density when only 2Mno.3O2 was used as the cathode active material and when the cathode active material was used as the cathode active material having the coating layer of Reference Example 2, the cathode active materials were subjected to powder rolling The density was confirmed, and the results are shown in Figs. 4 and 5.

 4 and 5, when the lithium transition metal oxide having the compositions of Reference Examples 1 and 2 is used, it can be confirmed that the rolling density is lowered by the formation of the coating layer. This is because the lithium transition metal oxide of the above composition has a high rolling density while the BET of the lithium manganese oxide of the present invention is lower than that of the lithium manganese oxide of the present invention to further form a coating layer, This is because it interferes with rolling.

<Experimental Example 2>

Each of the cathode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was used, and PVdF as a binder and Super-P as a conductive material were used. The positive electrode active material: binder: conductive material was mixed well with NMP at a weight ratio of 90: 5: 5, and then coated on A1 foil having a thickness of 20 /. The resultant was dried at 130 ^° C and then rolled so as to have an electrode porosity of 30% To prepare positive electrodes.

 Artificial graphite was used as the negative electrode active material and an artificial graphite conductive material (Super-P): binder (PVdF) was added to NMP as a solvent at a weight ratio of 95: 2.5: 2.5 to prepare a negative electrode mixture slurry, The negative electrode was prepared by coating on foil at 70 // m, drying and pressing at 130 ° C.

A polyethylene film (Celgard, thickness: 20 / ΛΠ) and a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a ratio of 1: 2: 1 Secondary batteries were prepared using a liquid electrolyte in which 1 M of LiPF ₆ was dissolved in a co-solvent.

 The secondary batteries were subjected to a rate test in the voltage range of 2.5 V to 4.6 V, and the results are shown in Table 1 below.

[Table 1]

Referring to Table 1, it can be seen that when the coating layer is formed by the content according to the present invention, a better rate characteristic is exhibited as compared with the case where no coating layer is formed (Examples 1 to 4 and Comparative Example 1) . Also, referring to Examples 1 and 2 and Comparative Example 2, when the content of the coating layer is too much to form a coating layer, it is confirmed that the rate characteristic is rather reduced. This is because the coating layer acts as a resistance .

In Comparative Example, such as 3, a coating when layers are in a molar ratio of the transition metal compared to Li _1:. Due to the perfect layered structure unfavorable to the Li diffusion, and, as shown in Comparative Example 4, the coating layer contains all of the Ni, Mn, Co It can be confirmed that the rate characteristic is decreased because a metal oxide phase which may interfere with the movement of lithium ions as much as Li is insufficient may be formed. While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

 [Industrial applicability]

 As described above, the cathode active material according to the present invention has a lithium-deficient transition metal oxide having a lithium-deficient state in which the molar ratio of the transition metal to the transition metal is less than 1, The inclusion of manganese based oxides (Mn> 5) improves the rolling density by reducing the surface roughness, but also the coating of lithium-deficient transition metal oxides based on Ni, Mn, and Co The electric conductivity is improved and the lithium ion diffusion property is improved according to the lithium deficiency, and the charge / discharge ratio characteristic of the secondary battery including the lithium ion diffusion property is improved.

 In addition, since the coating layer can also act as an active material, the decrease in the mass of the active material due to the increase in the mass of the coating layer is lower than that of the conventional coating composition, and the capacity decrease can be prevented.

Claims

Claims:

 [Claim 1]

1. A positive electrode active material comprising a lithium-excess lithium manganese-based oxide, wherein the lithium-excess lithium manganese-based oxide is represented by the following chemical formula (1), Li _{1 + a} Ni _x CoyMn _zv 0 _2- bAb

 Where 0 <a <0.2, 0 <x <0.4, 0 <y <0.4, 0.5 <z <0.9, 0 <v <0.2, a + x + y + z + v = 1, 0 <b <0.5; M is one or more elements selected from the group consisting of Al, Zr, Zn, Ti, Mg, Ga, In, Ru, Nb and Sn;

 A is one or more elements selected from the group consisting of P, N, F, S and Cl;

 Wherein a coating layer comprising a lithium-deficient transition metal oxide having a lithium-deficient state is formed on the surface of the lithium-excess lithium manganese-based oxide, wherein the molar ratio of lithium to transition metal is less than 1,

The amount of the coating layer is 1 wt. _^0/0 to 10% by weight of the positive electrode active material based on the total weight of the positive electrode active material.

 [Claim 2]

 The positive active material according to claim 1, wherein the lithium-deficient transition metal oxide is represented by the following formula (2)

Li _a 'Me0 ₂ (2)

 Where 0 < a &lt; l,

 Me is at least two elements selected from the group consisting of Ni, Co, and Mn.

 [Claim 3]

The method of claim 2, wherein Me = Ni _x 'Co _y ' Mn _z 'wherein 0 <x'<1, 0 <y '<1, 0 <z'<1, x '+ y' + z ' = l).

 Claim 4

 4. The cathode active material according to claim 3, wherein 0 <x '? 0.7, 0 < y'? 0.7, and 0.2 <z '? 0.6.

[Claim 5] The positive electrode active material according to claim 1, wherein the molar ratio of lithium to transition metal in the lithium-deficient transition metal oxide is 0.5 to 0.9.

 [Claim 6]

 The cathode active material according to claim 1, wherein the thickness of the coating layer is 30 nm to 200 nm.

 7.

 A method for producing the cathode active material according to claim 1,

 (i) a process in which a lithium-deficient transition metal oxide having lithium-deficient lithium manganese-based oxide and a lithium-deficient transition metal oxide contained in a molar ratio of lithium to transition metal is less than 1;

 (ii) heat treating the impurities of step (i);

 / RTI &gt;

The Lyrium-process for producing a positive electrode that is deficient transition heunhap to include 1 weight _^0/0 to 10% by weight based on the total weight of the metal oxide active material-deficient transition metal oxide is lithium manganese oxide and lithium in lithium excess.

 [8]

 The method of manufacturing a cathode active material according to claim 7, wherein the sputtering is dry sputtering.

9]

 The method of manufacturing a cathode active material according to claim 7, wherein the heat treatment is performed at 600 to 1100 degrees centigrade.

 [Claim 10]

 A positive electrode in which a positive electrode mixture containing the positive electrode active material according to claim 1 is formed on a current collector.

 Claim 111

 A secondary battery comprising a positive electrode according to claim 10.