KR20130117016A - Cathode active material having structure of high stability and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An anode active material is provided to manufacture a lithium secondary battery having excellent cyclic property and rate characteristic since the structural deformation is prevented and the structural stability and performance in the high temperature are improved by inhibiting the elution of manganese. CONSTITUTION: An anode active material comprises lithium nickel manganese complex oxide. A material inhibiting the elution of manganese is coated on the surface of the lithium nickel manganese complex oxide. The lithium nickel manganese complex oxide is represented by the chemical formula 1: Li1+bNi0.5-aMn1.5+aO4-c. In the chemical formula 1, -0.1<=a<=0.4, -0.1<=b<=0.1, and -0.1<=c<=0.1. The average particle diameter of the coated lithium nickel manganese complex oxide is 3-20 micron.

Description

A cathode active material having excellent structural stability and a lithium secondary battery including the same {Cathode Active Material Having Structure of High Stability and Lithium Secondary Battery Comprising the Same}

The present invention relates to a cathode active material having excellent structural stability and a lithium secondary battery including the same, and more particularly, to a cathode active material including lithium nickel manganese complex oxide (LNMO). The present invention relates to a cathode active material and a lithium secondary battery comprising the same, wherein a material having an effect of inhibiting manganese elution is coated on an oxide surface.

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 being actively carried out, and some are commercialized.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on a current collector. The negative electrode active material is mainly composed of a carbon-based material, and the positive electrode active material is mainly composed of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium composite oxide.

In particular, lithium manganese composite oxides having a spinel structure have been studied in recent years because they have advantages in terms of safety and cost compared to other cathode active materials having a potential of about 4V (volt).

However, the material has a disadvantage in that the life characteristics are poor because the capacity decreases severely as the charge / discharge cycle proceeds. This causes to vary, leading to the cause by the non-uniform reaction of manganese (Mn ³⁺⁾ in the lithium manganese spinel compound is decomposed into Mn ²⁺ and Mn ⁴⁺ type in that Mn ²⁺ is eluted (dissolution) in an electrolyte Because..

Accordingly, even in the case of using a compound having a spinel structure in which a part of Mn of LiMn ₂ O ₄ is replaced with Ni, in order to obtain a lithium secondary battery having an operating potential of 5 V, manganese elution problem still remains. Remains.

Therefore, there is a high necessity for a secondary battery technology capable of securing cycle performance by securing structural stability under high voltage conditions without causing such a problem.

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

After extensive research and various experiments, the inventors of the present application confirmed that the desired effect can be achieved when coating a material having a manganese elution inhibitory effect on the surface of the LNMO, as described later. The present invention has been completed.

Accordingly, the present invention provides a cathode active material comprising a lithium nickel manganese complex oxide (LNMO), a material having a manganese elution inhibitory effect is coated on the surface of the lithium nickel manganese oxide. do.

The lithium nickel manganese composite oxide may be preferably represented by the following formula (1), more preferably, LiNi _0.5 Mn _1.5 O ₄ It can be.

Li _{1 + b} Ni _0.5-a Mn _{1.5 + a} O _4-c (1)

Where

-0.1≤a≤0.4, -0.1≤b≤0.1 and -0.1≤c≤0.1.

In one preferred example, the material having a manganese elution inhibitory effect may be a metal oxide.

Representative examples of such metal oxides include metavanadate, and preferred examples thereof include compounds represented by the following formula (2).

M (VO ₃ ) _Z (2)

Wherein M is at least one selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd, and z is determined according to the oxidation number of M.

In another preferred embodiment, the manganese elution inhibitory material may be a ferroelectric material, preferably, BaTiO ₃ , (Ba, Sr) TiO ₃ , PbTiO ₃ , LiNbO ₃ , Pb (Zr, Ti) O ₃ , Amorphous V ₂ O _{5 It} may be any one or two or more selected from the group consisting of, more preferably PbTiO ₃ It may be.

The coating thickness of the material having a manganese elution inhibiting effect may be preferably 0.1 to 10 μm, and the average particle diameter of the coated lithium nickel manganese composite oxide may be preferably 3 to 20 μm.

The material having a manganese elution inhibiting effect may be applied to all or part of the surface of the lithium nickel manganese composite oxide, and the coating amount may be 80% to 100% of the surface of the lithium nickel manganese composite oxide.

The present invention also provides a lithium secondary battery positive electrode including the positive electrode active material and a lithium secondary battery including the positive electrode.

As described above, the positive electrode active material according to the present invention is applied to the surface of the LNMO having a manganese elution inhibitory effect, thereby suppressing the elution of manganese in the positive electrode active material to prevent structural deformation and structural stability and high temperature storage Performance improvement enables the production of a lithium secondary battery having excellent cycle characteristics, rate characteristics (C-rate), and the like.

As described above, the present invention provides a cathode active material including lithium nickel manganese composite oxide (LNMO), and a cathode active material coated with a material having a manganese elution inhibitory effect on the surface of the lithium nickel manganese oxide.

Lithium secondary batteries using LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ as a cathode active material have a 4V class operating potential and an average operating potential of 3.6 to 3.8V, which means oxidation of Co ions, Ni ions, or Mn ions. This is because the potential is determined by reduction. In contrast, when a lithium nickel manganese composite oxide (LNMO), a compound having a spinel structure in which a part of Mn of LiMn ₂ O ₄ is substituted with Ni, is used as a positive electrode active material, a lithium secondary battery having a 5 V operating potential can be obtained. It is possible.

For example, the lithium nickel manganese composite oxide (LNMO) may be preferably a compound represented by the following formula (1).

Li _{1 + b} Ni _0.5-a Mn _{1.5 + a} O _4-c (1)

The lithium nickel manganese composite oxide (LNMO) exhibits potential flatness in a region of 4.5V or more. In this high voltage spinel type cathode active material, Mn is present in a Mn ⁴⁺ state, and an operating voltage is determined by a Ni ²⁺ / Ni ⁴⁺ redox reaction instead of a redox reaction of Mn ³⁺ / Mn ⁴⁺ .

That is, the reduction of capacity due to Mn ³⁺ ions is reduced due to Ni ²⁺ substitution, and insertion and desorption of lithium ions stabilized to Ni ²⁺ / Ni ⁴⁺ by redox reaction in the 4.7 V voltage range is possible. do.

On the other hand, considering the battery characteristics, LiNi _0.5 Mn _1.5 O _{4 which} can be -0.1≤a≤0.4, -0.1≤b≤0.1, -0.1≤c≤0.1 in consideration of specific capacity, high voltage safety, etc. This may be particularly desirable.

When the lithium nickel manganese composite oxide (LNMO) is applied with a metal oxide such as metavanadate, the resulting coating layer is chemically stable to block the reaction between the electrolyte and LNMO and to suppress the elution of Mn from the spinel to improve the life characteristics. In addition, lithium, which has moved to the negative electrode in the first charging process of the lithium secondary battery, contributes to the formation of irreversible lithium which does not return to the positive electrode upon discharge. The irreversible lithium is a negative active material during the first charging process of the lithium secondary battery. It also serves to improve the battery capacity by reducing the consumption of reversible lithium by being consumed in the formation of the electrolyte membrane formed on the surface of the film.

In addition, when lithium nickel manganese composite oxide (LNMO) is coated with a ferroelectric material, which is another material having an effect of inhibiting the leaching of manganese, the ferroelectric material makes the charge distribution on the surface of the LNMO particles uniform and the movement of lithium ions by polarization. It plays a role of suppressing the elution of Mn quickly, and suppresses the deterioration of performance during high temperature storage.

The coating thickness of the material having a manganese elution inhibiting effect may be 0.1 to 10 μm. If the coating thickness is too thick, the resistance increases, and if the coating thickness is too thin, it is difficult to expect the effect of coating.

The present invention also provides a cathode for a lithium secondary battery including the cathode active material.

The positive electrode is prepared by applying a mixture of a positive electrode active material, LNMO, a conductive material and a binder on a positive electrode current collector, then drying and pressing, and optionally a filler is further added to the mixture.

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 changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface 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 usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. 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; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. 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 filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention also provides a lithium secondary battery comprising the positive electrode, the negative electrode, the separator and a lithium salt-containing nonaqueous electrolyte.

The negative electrode is manufactured by coating, drying, and pressing a negative electrode active material on a negative electrode current collector, and optionally, the conductive material, binder, filler, etc. may be further included as necessary.

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 electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a 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.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide 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 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 nonaqueous electrolyte is composed of a nonaqueous electrolyte and lithium. A nonaqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte and the like are used as the nonaqueous electrolyte, but are not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, 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, A polymer containing an ionic dissociation group and the like may 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, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

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

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

In a preferred _{embodiment, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (14)

 A cathode active material comprising lithium nickel manganese complex oxide (LNMO), wherein a material having a manganese elution inhibiting effect is coated on a surface of the lithium nickel manganese oxide. The cathode active material according to claim 1, wherein the lithium nickel manganese composite oxide is represented by the following general formula (1).
Li _{1 + b} Ni _0.5-a Mn _{1.5 + a} O _4-c (1)
In the formula, -0.1≤a≤0.4, -0.1≤b≤0.1, -0.1≤c≤0.1. The cathode active material according to claim 2, wherein the lithium nickel manganese composite oxide is LiNi _0.5 Mn _1.5 O ₄ . The cathode active material according to claim 1, wherein the coated lithium nickel manganese composite oxide has an average particle diameter of 3 to 20 µm. The cathode active material according to claim 1, wherein the material having a manganese elution inhibiting effect is a metal oxide. The cathode active material according to claim 5, wherein the metal oxide is metavanadate represented by the following general formula (2):
M (VO ₃ ) _Z (2)
Wherein M is at least one selected from the group consisting of Ni, Co, V, Ti, Zr, Cr, Mn, Cu, Zn, Ga, and Gd, and z is determined according to the oxidation number of M. The cathode active material according to claim 1, wherein the material having a manganese elution inhibiting effect is a ferroelectric material. The method of claim 7, wherein the ferroelectric material is any one selected from the group consisting of BaTiO ₃ , (Ba, Sr) TiO ₃ , PbTiO ₃ , LiNbO ₃ , Pb (Zr, Ti) O ₃ and Amorphous V ₂ O ₅ Cathode active material, characterized in that more than two. The cathode active material of claim 8, wherein the ferroelectric material is PbTiO ₃ . The cathode active material according to claim 1, wherein the material having a manganese elution inhibiting effect is coated on the whole or part of the surface of the lithium nickel manganese composite oxide. The cathode active material according to claim 1, wherein the material having a manganese elution inhibiting effect is coated with 30% to 100% of the surface of the lithium nickel manganese composite oxide. The cathode active material according to claim 1, wherein the coating thickness of the substance having a manganese elution inhibiting effect is in a range of 0.1 nm to 10 µm. A cathode for a lithium secondary battery, comprising the cathode active material according to any one of claims 1 to 12. A lithium secondary battery comprising the positive electrode according to claim 13.