KR20130008780A - Composite electrode comprising different electrode active material coating layers and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: A composite electrode in which heterogeneous electrode active material layer is coated and a lithium secondary battery including the same are provided to enhance stability and low temperature output properties. CONSTITUTION: A composite electrode comprises a first electrode which shows 1 phase reaction in discharging process and in which one or more electrode active materials selected from chemical formula 1 is coated; and second electrode which shows 2 phase reaction in discharging process and in which one or more electrode active materials selected from chemical formula 2 is coated. The chemical formula 1 is as follows: Li (Li xM (1-x)M' y) O (2-t). The chemical formula 2 is as follow: (1-z) Li aM" xP (1-x-y) A yO (4-b*z) C.

Description

A composite electrode coated with a different electrode active material layer and a lithium secondary battery including the same {Composite Electrode Comprising Different Electrode Active Material Coating Layers and Lithium Secondary Battery Comprising the Same}

The present invention relates to a composite electrode and a lithium secondary battery including the same, and more particularly, a one-phase reaction during a discharge process and one or more electrode active materials selected from the following Chemical Formula 1 are applied to the current collector. And a second electrode having a two-phase reaction having a lower voltage than the first electrode and having one or more electrode active materials selected from the following Chemical Formula 2 applied to the current collector. It relates to a composite electrode and a lithium secondary battery comprising the same.

Among the secondary batteries that are rapidly increasing in demand, lithium secondary batteries having high energy density and voltage, long cycle life, and low self discharge rate are commercially used.

In addition, as interest in environmental issues grows, research on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, is being conducted. It is becoming. Although a nickel-metal hydride secondary battery is mainly used as a power source of such an electric vehicle and a hybrid electric vehicle, research using a lithium secondary battery having a high energy density and a discharge voltage has been actively conducted, and some commercialization has been made.

As a negative electrode active material of such a lithium secondary battery, a carbon material is mainly used, and use of lithium metal, a sulfur compound, a silicon compound, a tin compound, etc. is also considered. Examples of the positive electrode active material include lithium manganese oxides such as lithium cobalt oxide (LiCoO ₂ ), layered crystal structure LiMnO ₂ , spinel crystal structure LiMn ₂ O ₄ , transition metal oxides such as lithium nickel oxide (LiNiO ₂ ), Complex oxides such as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , in which some of these transition metals are substituted with other transition metals, are used. Recently, the use of lithium transition metal phosphates such as LiFePO _{4 is} also considered. have.

Some of the lithium transition metal oxides in the cathode active material have a very high capacity, but relatively poor in safety, and exhibits a one-phase reaction with a large slope during charging and discharging. There is a problem losing.

On the other hand, among the materials exhibiting a two-phase reaction, it has the advantages of excellent safety due to its structural stability and excellent output characteristics according to the charge / discharge section, but low density and voltage, and electrical conductivity There are low materials. In order to improve the low electrical conductivity, when the carbon coating or the like is used, the electrode density is low, and thus the battery capacity is very low.

In this regard, some prior arts mix heterogeneous oxides such as using a mixture of lithium nickel cobalt manganese composite oxide and lithium manganese oxide as a cathode active material or a mixture of lithium composite oxide and lithium cobalt oxide having a layered crystal structure. A technique for producing a cathode active material is disclosed. However, it was confirmed that the positive electrode active material formed by mixing different oxides as described above does not have a great effect of supplementing physical properties by mixing.

Furthermore, when a lithium composite oxide having a layered crystal structure and lithium iron phosphate are mixed as a cathode active material, lithium iron phosphate having low conductivity lowers the conductivity of the entire electrode or lowers the electrode density of the entire active material. .

Therefore, there is a high need for a technique for solving this 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 in-depth study and various experiments, the inventors of the present application have a specific electrode active material exhibiting a one-phase reaction during discharge and a specific electrode exhibiting a two-phase reaction having a lower voltage. The active material was applied to the current collector to form a separate electrode to form a separate electrode, this composite electrode was confirmed that the safety and low-temperature output characteristics can be improved while minimizing the increase in resistance due to the simple mixing of the active material The present invention has been completed.

Accordingly, the composite electrode according to the present invention may include a first electrode in which a one-phase reaction occurs during a discharge process and one or more electrode active materials selected from Chemical Formula 1 are applied to a current collector, and the first electrode. It is composed of a second electrode having a two-phase reaction with a lower voltage than the electrode and having one or more electrode active materials selected from the following Chemical Formula 2 coated with a current collector.

Li (Li _x M _{1 - x} M ' _y ) O _2-t (1)

Where

0 ≦ x <0.5, 0 ≦ y <0.1, −0.1 <z <0.1, −0.1 <t <0.1;

M is one or more transition metals selected from monocyclic transition metals;

M 'is one or more selected from metals and metalloids having a stable structure at 6 coordination,

(1-z) Li _a M " _x P _{1 -x- y} A _y O _{4 -b} * zC (2)

Where

0.8 <a ≦ 1.3, 0 ≦ x <0.5, 0 ≦ y <0.1, 0 ≦ z <0.1, −0.1 <b <0.1;

M ″ is at least one selected from monocyclic transition metals and metals and metalloids having a structure stable to six coordination;

A is selected from metals and metalloids which are stable in the four coordination structure.

As described above, when the active material is simply mixed and used, since the properties of the mixture are exhibited rather than the optimal properties of each active material, the effect of supplementing physical properties due to the mixing is not large and there is a problem in that the resistance is increased.

On the other hand, the composite electrode according to the present invention is composed of heterogeneous electrodes coated with different kinds of active materials, so that the characteristics of the active materials can be maximized, and the power accompanying the increase in resistance Deterioration of the power characteristic can be minimized.

Specifically, since the active materials of different specific characteristics are coated on the electrode current collectors, respectively, to form heterogeneous electrodes, not only are they complementary in terms of physical properties, but may exhibit synergistic effects due to different electrode active materials. As a result, the characteristics of each of the active materials can be exhibited to the maximum as compared with the case of simply mixing the active materials.

The composite electrode according to the present invention may be a positive electrode. The positive electrode is manufactured by coating and drying a positive electrode active material on a current collector as an electrode active material, respectively.

The compound of Chemical Formula 1 or Chemical Formula 2 according to the present invention may preferably be lithium transition metal oxide or lithium iron phosphate having a layered crystal structure.

In general, the lithium-transition metal oxide having a layered crystal structure has a high capacity but is relatively inferior in safety, and lithium iron phosphate has an advantage that the electrical conductivity is low, but the safety is excellent due to the structural stability. Therefore, in the case of a composite electrode using a specific lithium transition metal oxide having a layered crystal structure and a specific lithium iron phosphate as a heterogeneous cathode active material, lithium iron phosphate having excellent capacity characteristics and excellent safety has a lithium of a layered crystal structure. As it serves as a separator of the transition metal oxide, the safety of the battery may be further increased.

In addition to the positive electrode active material, Li _x (Ni _v Mn _w Co _y M _z ) O _{2- t} A _t In the above formula, 0.8 <x≤1.3, 0≤v≤0.9, 0≤w≤0.9, 0≤y≤0.9, 0≤z≤0.9, x + v + w + y + z = 2, 0≤t <0.2; M is at least one metal or transition metal cation of +2 to + 4-valent oxidation water; A is a -1 or -divalent anion), Li _a Mn _2-b M ' _b O _4-c A' _c Wherein 0.8 <a≤1.3, 0≤b≤0.5, 0≤c≤0.3; M 'is at least one metal or transition metal cation of +2 to + 4-valent oxidation number; A' is -1 or- Divalent anions), disulfide compounds, Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

As described above, the composite electrode according to the present invention can minimize the increase in resistance due to the simple mixing of the electrode active materials, can improve the safety, and such a composite electrode exhibits excellent low-temperature output characteristics than the prior art. It can be used for the production of a lithium secondary battery.

The positive electrode active material according to the present invention may optionally include a conductive material, a binder, a filler, and the like to constitute a positive electrode mixture.

The conductive material 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 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 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 inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The positive electrode for a secondary battery may be manufactured by, for example, applying a slurry made by mixing the positive electrode mixture with a solvent such as NMP onto a positive electrode current 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.

In the composite electrode according to the present invention, the negative electrode active material is a carbon-based negative electrode active material, titanium containing oxide, 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': Al, B, P, Si, Group 1 of the Periodic Table, Group 2, Group 3 element, a halogen; 0 <x≤1; 1 Metal composite oxides such as ≦ y ≦ 3 and 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used, but are not limited thereto.

Such a negative electrode active material, if necessary, comprises the components as described above to constitute a negative electrode mixture.

The negative electrode for a secondary battery may be prepared by, for example, applying a slurry made by mixing the negative electrode mixture with a solvent such as NMP onto a negative electrode current collector, followed by drying and rolling.

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 present invention also provides an electrode assembly for a secondary battery, comprising the composite electrode and a porous separator interposed between the composite electrode.

The porous separator prevents a short circuit 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; Sheets or nonwovens made of glass fibers or polyethylene are 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 electrode assembly for a secondary battery according to the present invention may be manufactured in various forms, for example, a jelly-roll type, a stack type, a stack / fold type or a stack / zigzag folding type, and the like. It may be a cylindrical can, a rectangular can, or a shape embedded in a battery case of a laminate sheet including a metal layer and a resin layer. Since this is well known in the art, a detailed description thereof will be omitted.

The present invention provides a secondary battery comprising the electrode assembly.

The secondary battery according to the present invention may preferably be a lithium secondary battery, and in particular, may be preferably applied to a so-called lithium ion polymer battery, in which a lithium-containing non-aqueous electrolyte is impregnated into the electrode assembly in the form of a gel.

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.

As the inorganic solid electrolyte, for example, 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 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 lithium secondary battery according to the present invention may not only be usefully used in a battery cell used as a power source for a small device, but also as a unit battery in a medium and large battery module including a plurality of battery cells used as a power source for a medium and large device. It can be used preferably. Moreover, it can be preferably used for medium-large battery modules that require high rate characteristics, power characteristics, and the like depending on the operating conditions and require long-term use.

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); Electric golf cart; Power storage devices, etc., but is not limited thereto.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (6)

In the discharge process, a one-phase reaction (1 phase reaction) and one or more electrode active material selected from the following formula (1) is applied to the current collector, and a two-phase reaction (lower voltage than the first electrode) A composite electrode, characterized in that it comprises a second electrode having a current collector applied to one or more electrode active material selected from the formula (2)
Li (Li _x M _{1 - x} M ' _y ) O _2-t (1)
In this formula,
0 ≦ x <0.5, 0 ≦ y <0.1, −0.1 <z <0.1, −0.1 <t <0.1;
M is one or more transition metals selected from monocyclic transition metals;
M 'is one or more selected from metals and metalloids having a stable structure at 6 coordination,
(1-z) Li _a M " _x P _{1 -x- y} A _y O _{4 -b} * zC (2)
In this formula,
0.8 <a ≦ 1.3, 0 ≦ x <0.5, 0 ≦ y <0.1, 0 ≦ z <0.1, −0.1 <b <0.1;
M ″ is at least one selected from monocyclic transition metals and metals and metalloids having a structure stable to six coordination;
A is selected from metals and metalloids which are stable in the four coordination structure. The electrode assembly for a secondary battery, characterized in that consisting of a porous separator is interposed between the composite electrode according to claim 1. A lithium secondary battery comprising the electrode assembly of claim 2. A battery module comprising using the lithium secondary battery according to claim 3 as a unit cell. An electric vehicle or a hybrid electric vehicle, comprising using the battery module according to claim 4 as a power source. A power storage device using the battery module according to claim 5 as a power source.