KR101447484B1 - Positive electrode active material for secondary battery - Google Patents

Abstract

The present invention provides a positive electrode active material for a secondary battery, which has a composition represented by the following formula (1), and has the form of a solid solution or a composite, and a secondary battery comprising the same.
xLi ₂ MO ₃ + yLiM'O ₂ + zLi ₂ M " ₂ O ₄ (1)
In the above equation, 0 <x <0.7, 0.2 <y <0.9, 0 <z <0.7, x + y + z = 1, and M is one species selected from one cycle or two cycle transition metals having an average oxidation number + And M 'is at least one element selected from one cycle or two cycle transition metals having an average oxidation number of +3 and M "is at least one element selected from the group consisting of a single cycle or a four cycle transition metal having a combination of an average oxidation number of +3 and +4 It is at least one element selected.

Description

[0001] The present invention relates to a positive electrode active material for a secondary battery,

The present invention relates to a positive electrode active material for a secondary battery, which has a specific mixed composition and is excellent in stability and capacity at a high voltage.

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, Are being studied extensively. 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.

In particular, a lithium secondary battery used in an electric vehicle should have a high energy density and a capability to exhibit a large output in a short time, and can be used for more than 10 years under harsh conditions. Therefore, Life characteristics are inevitably required. In addition, a secondary battery used in an electric vehicle (EV), a hybrid electric vehicle (HEV) and the like requires excellent rate characteristics and power characteristics depending on the operating conditions of the vehicle.

Lithium ion secondary batteries used in conventional small batteries generally use a layered lithium cobalt composite oxide as the positive electrode and a graphite based material as the negative electrode. However, in the case of the lithium cobalt composite oxide, Cobalt is very expensive and has a disadvantage in that it is unsuitable for electric vehicles in terms of safety. Therefore, a lithium manganese composite oxide having a spinel structure composed of manganese which is inexpensive and excellent in safety can be suitable as the anode of a lithium ion battery for electric vehicles.

However, in the case of the lithium manganese composite oxide, manganese is eluted into the electrolyte due to the influence of the electrolytic solution at high temperature and high current charging / discharging, degrading the battery characteristics, and therefore an improvement measure is needed. In addition, since the capacity per unit weight is smaller than that of the conventional lithium-cobalt composite oxide or lithium-nickel composite oxide, there is a limitation in increasing the capacity per cell weight, As shown in Fig.

In order to compensate for these disadvantages, materials such as Li (Ni _x Mn _y Co _z ) O ₂ (x + y + z = 1) have been recently used. In order to secure the structural stability of the layered cathode active material, Li ₂ MnO ₃ as a cathode active material.

In order to secure the structural stability of such a layered cathode active material, many researchers are studying a layered cathode active material containing Li ₂ MnO ₃ . The cathode active material having the layered structure containing Li ₂ MnO ₃ is characterized in that Li is contained in the transition metal layer of a general LiMO ₂ (M: transition metal), and a specific arrangement peak (Li ₂ MnO ₃₎ lattice peaks. These materials have a high Mn content and are very inexpensive and have a very large and stable capacity at high voltage. The material has a flat section at 4.4 to 4.6 V and shows an increase in capacity after activation for this flat section. It is known that the increase of the capacity is caused by the release of Li of the transition metal layer due to the generation of oxygen, but it is still controversial.

However, it is clear that after the activation period of this capacity, the change in structure is severe and the electrical characteristics deteriorate. This is because it is known that the transition from the layered structure to the spinel structure occurs due to the structural change, and the contact between the domains is loosened. Due to this characteristic, it is impossible to use it in actual cells at present.

In some prior arts, attempts have been made to coat the particles after synthesis of the active material to solve the above problems, but this method has a problem of causing an increase in manufacturing cost. Further, since the above method is post-treatment method, it does not contribute to the substantial change and improvement of the internal structure, since most structural changes are made by the process of forming a crystal at a high temperature of the synthesis process.

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.

As a result of extensive research and various experiments, the inventors of the present application have developed a cathode active material for a secondary battery having a mixed composition represented by the general formula (1) as a cathode active material for a secondary battery, It has been confirmed that not only an increase in capacitance but also an electrical characteristic are obtained after the activation period, and thus the present invention has been accomplished.

Accordingly, the present invention provides a cathode active material having a composition represented by the following general formula (1) and having a solid solution or a composite form.

xLi ₂ MO ₃ + yLiM'O ₂ + zLi ₂ M " ₂ O ₄ (1)

In the above equation, 0 <x <0.7, 0.2 <y <0.9, 0 <z <0.7, x + y + z = 1, and M is one species selected from one cycle or two cycle transition metals having an average oxidation number + And M 'is at least one element selected from a single-cycle or two-cycle transition metal having an average oxidation number of +3 and M "is at least one element selected from the group consisting of one cycle or four cycle transition metal &Lt; / RTI &gt;

The range of z in the above formula (1) is preferably 0 < z < 0.1.

In the above formula (1), M 'is preferably a combination of two or more kinds of transition metals satisfying the above conditions.

In the above formula (1), M is preferably one or more elements selected from the group consisting of Mn, Sn, Ti and Zr as the transition metal satisfying the above conditions.

M 'in Formula 1 is preferably at least one transition metal selected from the group consisting of Ni, Mn, and Co.

In the above formula (1), M "is preferably at least one element selected from the group consisting of Ni and Mn as a transition metal satisfying the above conditions.

The present invention provides a positive electrode material mixture comprising the positive electrode active material.

The present invention also provides a lithium secondary battery comprising the positive electrode for a secondary battery and the positive electrode for the secondary battery, characterized in that the positive electrode mixture is coated on the current collector.

As described above, the positive electrode-based nonaqueous electrolyte secondary battery including the positive electrode active material having the specific mixed composition according to the present invention can provide a secondary battery having a high capacity and excellent electrical characteristics.

Hereinafter, the present invention will be described in further detail, but the following contents are intended to illustrate the present invention and the scope of the present invention is not limited thereto.

The present invention provides a cathode active material for a secondary battery having a composition represented by the following formula (1).

xLi ₂ MO ₃ + yLiM'O ₂ + zLi ₂ M " ₂ O ₄ (1)

In the above equation, 0 <x <0.7, 0.2 <y <0.9, 0 <z <0.7, x + y + z = 1, and M is one species selected from one cycle or two cycle transition metals having an average oxidation number + And M 'is at least one element selected from a single-cycle or two-cycle transition metal having an average oxidation number of +3 and M "is at least one element selected from the group consisting of one cycle or four cycle transition metal &Lt; / RTI &gt;

The positive electrode active material according to the present invention includes Li ₂ M " ₂ O ₄ having excellent electrical properties before the activation of the high potential described above, so that the structural stability can be secured by reducing the structural change after the activation period. Performance degradation can be minimized, but the principle is not clear from a structural point of view.

The cathode active material may be prepared by mixing a transition metal precursor with a lithium precursor such as lithium hydroxide or lithium carbonate, followed by calcining in a furnace. In addition, LiMnO ₂ is unstable when lithium is insufficient, and the active material may be split into Li ₂ MnO ₃ and Li ₂ Mn ₂ O ₄ .

The active material of Formula 1 may be a composite of a layered structure or may be in the form of a solid solution. In some cases, they may be present in a mixed form thereof.

When the content of Li ₂ M " ₂ O ₄ is excessively high in the above formula (1), there is a problem such as elution of manganese, so that the total amount is preferably less than 0.7, Particularly preferably less than 0.1.

In the above formula (1), M is preferably one or more elements selected from the group consisting of Mn, Sn, Ti and Zr as the transition metal satisfying the above conditions. Among them, Mn is particularly preferable.

In the above formula (1), M 'is preferably one or more elements selected from the group consisting of Mn, Ni and Co as a transition metal satisfying the above conditions, and more preferably two or more kinds thereof. In particular, a combination containing Mn as an essential component and optionally Ni and / or Co is preferable.

M "in the above formula (1) is preferably at least one element selected from the group consisting of Ni and Mn as a transition metal satisfying the above-mentioned conditions. Mg and Al. &Lt; / RTI &gt;

In some cases, at least one or more of the transition metals (M, M ', or M ") in Formula 1 may be doped with another element that may be located in the 6-coordinate structure. The substitution amount of the metal or nonmetal element that can be contained is preferably 10 mol% or less based on the total amount of the transition metal. When the substitution amount is too large, it is difficult to secure a desired level of capacity.

In the above formula (1), the oxygen (O) ion may be substituted with another anion in a predetermined amount range. The other anion may preferably be at least one element selected from the group consisting of halogen elements such as F, Cl, Br and I, sulfur, chalcogenide elements, and nitrogen.

Such anion substitution has an advantage in that the binding force with the transition metal is excellent and the structural transition of the active material is prevented. However, if the substitution amount of the anion is too large, the compound may not maintain a stable structure and the lifetime characteristics may be deteriorated. Therefore, the preferable substitution amount of the anion is 20 mol% or less, more preferably 10 mol% or less based on the total amount of anion including oxygen.

The present invention also provides a positive electrode material mixture comprising the positive electrode active material. In addition to the cathode active material, the cathode mixture according to the present invention may optionally contain a conductive agent, a binder, a filler, and the like.

The conductive agent is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive agent is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive 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, and various copolymers.

The filler is optionally used as a component for suppressing 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-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention provides a positive electrode for a secondary battery in which the positive electrode material mixture is applied on a current collector. The positive electrode according to the present invention can be manufactured by applying a slurry prepared by mixing a positive electrode material mixture containing a positive electrode active material as described above with a solvent such as NMP, coating the positive electrode current collector, and drying and rolling.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel 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 present invention also provides a lithium secondary battery comprising the positive electrode, the negative electrode, the separator, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode is prepared, for example, by coating a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the mixture. The negative electrode mixture may contain the above-described components as required.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, 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 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 solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

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 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.

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 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), FEC (fluoro-ethylene carbonate), and the like.

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

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.

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 (9)

1. A cathode active material having a composition represented by the following formula (1) and having the form of a solid solution or a composite:
xLi ₂ MO ₃ + yLiM'O ₂ + zLi ₂ M " ₂ O ₄ (1)
In this formula,
0 <x <0.7, 0.2? Y? 0.9, 0 <z <0.7, x + y + z = 1;
M is at least one transition metal selected from the group consisting of Mn, Sn, Ti, and Zr;
M 'is at least one transition metal selected from the group consisting of Ni, Mn, and Co; And
M "is at least one transition metal selected from the group consisting of Ni and Mn. 2. The cathode active material according to claim 1, wherein z is 0 < z < 0.1. The positive electrode active material according to claim 1, wherein M 'is at least two elements. delete delete delete A positive electrode material mixture comprising the positive electrode active material according to any one of claims 1 to 3. A positive electrode for a secondary battery, wherein the positive electrode mixture according to claim 7 is applied on a current collector. A lithium secondary battery comprising the positive electrode for a secondary battery according to claim 8.