KR101392803B1 - Positive Electrode for Secondary Battery Comprising Cathode Active Material of Different Size, and Lithium Secondary battery Comprising the Same - Google Patents

Abstract

A positive electrode active material (a) having an average particle diameter of 8 to 20 탆 and a positive electrode active material (b) having an average particle diameter of 1 to 7 탆 in an amount of 90: 10: 95: 5 (a: b), and a lithium secondary battery comprising the same.

Description

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

The present invention relates to a positive electrode for a secondary battery of a positive electrode active material having different sizes, and a lithium secondary battery comprising the same, and more particularly to a positive electrode for a secondary battery comprising a positive electrode active material of different sizes, Wherein the positive electrode active material (a) having an average particle diameter of 1 to 7 占 퐉 and the positive electrode active material (b) having an average particle diameter of 1 to 7 占 퐉 are contained in a mixing ratio (a: b) of 90:10 to 95: 5 by volume, To a lithium secondary battery.

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 operating 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 it is in the stage of commercialization.

Lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode of such a lithium secondary battery, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, LiNiO ₂ ) is also being considered, and it is common to use a graphite-based material for the cathode.

Among the above cathode active materials, lithium-containing cobalt oxides are excellent in lifetime characteristics and charge / discharge efficiency, but they are inferior in high-temperature safety, and cobalt used as a raw material is a costly material because of resource limitations, Oxides exhibit a higher discharge capacity at a lower cost than the above cobalt oxides, but have a problem in that a rapid phase transition of the crystal structure occurs depending on the volume change accompanying the charge / discharge cycle.

Accordingly, a lithium-containing manganese oxide having a spinel crystal structure composed of manganese, which is inexpensive and excellent in safety, may be suitable as the anode of a lithium ion battery for an electric vehicle. However, in the case of the lithium-containing manganese oxide, manganese is eluted into the electrolytic solution due to the influence of the electrolytic solution when stored at a high temperature to degenerate the battery characteristics. Further, since the capacity per unit weight is smaller than that of conventional lithium-containing cobalt oxide and lithium-containing nickel oxide, there is a limit to an increase in the capacity per cell weight, and design of a battery for improving the capacity is required. It can be practically used.

Some prior art discloses a technique for a cathode active material composed of a lithium nickel composite oxide and a lithium manganese composite oxide having different average particle diameters in order to increase the volume density of the electrode plate to increase the capacity of the battery.

However, depending on the particle size and kind of the positive electrode active material, there is a problem that breakage of the active material particles and desorption of the mixture layer may occur in the high-density rolled mixed layer in the rolling step of applying and drying the active material to the positive electrode collector .

Accordingly, a structure of a secondary battery including an electrode that increases the capacity characteristics of the battery through high-polymerization of the electrode and does not damage the active material during the compression (rolling) process has not been proposed yet.

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.

The inventors of the present application have conducted intensive research and various experiments, and have found that, when the positive electrode is manufactured using the positive electrode active material satisfying the specific size condition and the mixing ratio condition, the capacity per volume of the positive electrode is improved without damaging the positive electrode active material in the rolling process And the present invention has been accomplished.

Accordingly, the cathode for a secondary battery according to the present invention is a cathode for a secondary battery comprising a cathode active material having different sizes, and includes a cathode active material (a) having an average particle diameter of 8 to 20 탆 and a cathode active material having an average particle diameter of 1 to 7 탆 b) is contained in a mixing ratio (a: b) of 90:10 to 95: 5 on a volumetric basis.

Regarding the particle size condition, it satisfies the condition that the average particle diameter of the positive electrode active material (a) is 8 to 20 탆 and the average particle diameter of the positive electrode active material (b) is 1 to 7 탆 as defined above, (a) has an average particle diameter of 8 to 16 占 퐉 and the average particle diameter of the positive electrode active material (b) is 3 to 7 占 퐉.

(A: b) of the positive electrode active material (a) and the positive electrode active material (b) is 90:10 to 95: 5 by volume, more preferably, , And 92: 8 to 94: 6.

The positive electrode active material (a) and the positive electrode active material (b) may have the same element composition or may have different element compositions.

As a preferred example, the cathode active material (a) and the cathode active material (b) may be compounds selected from the following formulas (1) to (5), respectively.

Li _x Co _{1 - y} M _y O ₂ A _a (1)

Mg, Ni, Mn, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, and Mo (where 0 <x < , Sr, Sb, W, and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;

Li _x Ni _{1 - y} M ' _y O _{2 a a} (2)

Mg, Mn, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, One or more elements selected from the group consisting of Mo, Sr, Sb, W and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;

Li _x Mn _{2 - y} M " _y O _{4 - aa a} (3)

Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, One or more elements selected from the group consisting of Mo, Sr, Sb, W and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;

Li _x Ni _{x '} Mn _y Co _{1 - ( x' + y)} O ₄ (4)

(0.8? X? 1.2, 0.2? X? 0.7, 0.2? Y? 0.7 and x '+ y <1);

Li _x M _{1 - y} M ' _y PO _{4 a a} (5)

S, Se, F, Cl, < / RTI &gt; &lt; RTI ID = 0.0 &gt; I, 6A and 7A elements).

The present invention also provides a lithium secondary battery comprising the positive electrode and the negative electrode.

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

Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric power storage systems, and the like.

As described above, the positive electrode-based lithium 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 energy density without damaging the active material during the rolling process of the positive electrode.

Hereinafter, the present invention will be further described with reference to Examples of the present invention, but the scope of the present invention is not limited thereto.

The positive electrode for a secondary battery according to the present invention is a positive electrode for a secondary battery including a positive electrode active material having different sizes. The positive electrode active material (a) having an average particle diameter of 8 to 20 탆 and the positive electrode active material (b) having an average particle diameter of 1 to 7 탆, Is contained in a mixing ratio (a: b) of 90:10 to 95: 5 on a volumetric basis.

As described above, the positive electrode for a secondary battery is prepared by applying a slurry prepared by mixing a positive electrode mixture containing a positive electrode active material or the like to a solvent such as NMP, coating the positive electrode collector, followed by drying and rolling. In the rolling process, generally, a large pressure is applied in order to increase the filling density of the electrode.

When the cathode active material is composed of particles having a single particle size, the voids between the particles are maximized, and there is a limitation in increasing the filling density without destroying the particles in the rolling process.

Therefore, although a method of using a mixture of particles having different average particle diameters as the cathode active material has been proposed, it has also been confirmed that a considerable number of particles are damaged in the rolling process for increasing the packing density.

On the other hand, it has been experimentally confirmed by the present inventors that, in the case of constituting the positive electrode satisfying the particle size condition and the mixing ratio condition defined in the present invention, surprisingly, it is possible to achieve a high capacity while minimizing the damage of the active material.

Regarding the particle size condition, it satisfies the condition that the average particle diameter of the positive electrode active material (a) is 8 to 20 탆 and the average particle diameter of the positive electrode active material (b) is 1 to 7 탆 as defined above, (a) has an average particle diameter of 8 to 16 占 퐉 and the average particle diameter of the positive electrode active material (b) is 3 to 7 占 퐉.

(A: b) of the positive electrode active material (a) and the positive electrode active material (b) is 90:10 to 95: 5 by volume, more preferably, , And 92: 8 to 94: 6.

When the average particle diameter and the mixing ratio exceed the above-mentioned conditions, it is difficult to expect an increase in capacity, or the active material particles may be broken or the separation of the anodic coalescing layer may occur during the rolling process.

The positive electrode active material (a) and the positive electrode active material (b) may have the same element composition or may have different element compositions.

As a preferred example, the cathode active material (a) and the cathode active material (b) may be compounds selected from the following formulas (1) to (5), respectively.

Li _x Co _{1 - y} M _y O ₂ A _a (1)

Mg, Ni, Mn, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, and Mo (where 0 <x < , Sr, Sb, W, and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;

Li _x Ni _{1 - y} M ' _y O _{2 a a} (2)

Mg, Mn, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, One or more elements selected from the group consisting of Mo, Sr, Sb, W and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;

Li _x Mn _{2 - y} M " _y O _{4 - aa a} (3)

Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, One or more elements selected from the group consisting of Mo, Sr, Sb, W and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;

Li _x Ni _{x '} Mn _y Co _{1 - ( x' + y)} O ₄ (4)

(0.8? X? 1.2, 0.2? X? 0.7, 0.2? Y? 0.7 and x '+ y <1);

Li _x M _{1 - y} M ' _y PO _{4 a a} (5)

S, Se, F, Cl, < / RTI &gt; &lt; RTI ID = 0.0 &gt; I, 6A and 7A elements).

The positive electrode for a lithium secondary battery according to the present invention may contain one or more components selected from a conductive material, a binder and a filler in addition to the positive electrode active material, and preferably includes both a conductive material and a binder.

The conductive material may be usually added in an amount of 1 to 30 wt% based on the total weight of the positive electrode material 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; 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 bonding of the active material and the conductive agent to the binder and in the current collector, and is usually added in an amount of 1 to 30 wt% based on the total weight of the positive electrode mixture. 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 content of the filler may be 0.1 to 15% by weight based on the total weight of the positive electrode material mixture.

As described above, such a positive electrode material mixture is applied onto the current collector to form a positive electrode for a secondary battery. For example, a slurry prepared by mixing the positive electrode material mixture with a solvent such as NMP may be coated on the positive electrode collector, followed by 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 and the negative electrode.

The negative electrode may be manufactured by preparing an anode mixture slurry using a negative electrode active material, applying the slurry to an anode current collector, and drying and rolling the mixture.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li y Fe 2 O 3 (0≤y≤1} ), Li y WO 2 (0≤y≤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 and the like can be used.

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 high conductivity without causing chemical changes in the battery, and examples thereof 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 anode may also optionally include components of the anode as described above.

The lithium secondary battery generally comprises an anode, a cathode, a separator, and a non-aqueous electrolyte containing a lithium salt.

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), FPC (fluoro-propylene 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 for a small device but also as a unit cell in a middle or large battery module including a plurality of battery cells.

Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric power storage systems, and the like.

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 (8)

A positive electrode active material (a) having an average particle diameter of 8 to 20 占 퐉 and a positive electrode active material (b) having an average particle diameter of 1 to 7 占 퐉 of 90:10 to 95 : 5 as a mixing ratio (a: b)
The positive electrode active material (a) and the positive electrode active material (b) have different element compositions,
Wherein the cathode active material is a compound selected from the group consisting of the following Chemical Formulas 1 to 4:
Li _x Ni _1-y M ' _y O _{2-aa a} (1)
Mg, Mn, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, One or more elements selected from the group consisting of Mo, Sr, Sb, W and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;
Li _x Mn _2-y M '' _y O _{4-aa a} (2)
Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb (where 0.8 <x <1.2, 0 = y = 1, 0 = , One or more elements selected from the group consisting of Mo, Sr, Sb, W and Bi, A = S, Se, F, Cl, I, 6A and 7A elements;
Li _x Ni _{x '} Mn _y Co _{1- (x' + y)} O ₄ (3)
(0.8 = x = 1.2, 0.2 = x '= 0.7, 0.2 = y = 0.7 and x' + y <1);
Li _x M _1-y M ' _y PO _{4-aa a} (4)
S, Se, F, Cl, and the like, wherein M = Al, Mg, or Ti; I, 6A and 7A elements). The positive electrode for a lithium secondary battery according to claim 1, wherein the positive electrode active material (a) having an average particle diameter of 8 to 16 탆 and the positive electrode active material (b) having an average particle diameter of 3 to 7 탆 are mixed. The positive electrode for a lithium secondary battery according to claim 1, wherein the mixing ratio (a: b) is 92: 8 to 94: 6. delete delete A lithium secondary battery comprising the positive electrode according to claim 1. The lithium secondary battery according to claim 6, wherein the lithium secondary battery is used as a unit battery of a battery module that is a power source of a middle- or large-sized device. 8. The lithium rechargeable battery of claim 7, 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.