KR101490842B1 - Composite Electrode Comprising Different Electrode Active Material Coating Layers and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a composite electrode and a lithium secondary battery comprising the same, and more particularly, to a composite electrode and a lithium secondary battery including the same. And a second electrode having a current collector coated with one or more electrode active materials selected from the group consisting of the following formula (2) and having a voltage lower than that of the first electrode (2 phase reaction) A lithium secondary battery is provided.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite electrode coated with a heterogeneous electrode active material layer, and a lithium secondary battery including the composite electrode.

The present invention relates to a composite electrode and a lithium secondary battery comprising the same, and more particularly, to a composite electrode which exhibits a one-phase reaction in a discharge process and has one or more electrode active materials selected from the following formula (1) And a second electrode coated with a current collector, wherein the electrode active material exhibits a two-phase reaction with a voltage lower than that of the first electrode and is selected from the following formula (2) A composite electrode and a lithium secondary battery comprising the composite electrode.

BACKGROUND ART [0002] Lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate have been widely used in secondary batteries, which have been rapidly increasing in demand in recent years.

In addition, as interest in environmental issues grows, research on electric vehicles and hybrid electric vehicles that can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, which are one of the major causes of air pollution, . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches on the use of lithium secondary batteries having high energy density and discharge voltage have been actively carried out and some of them have been commercialized.

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 and the like is also considered. Examples of the positive electrode active material include a lithium manganese oxide such as lithium cobalt oxide (LiCoO ₂ ), a layered crystal structure of LiMnO ₂ , a spinel crystal structure of LiMn ₂ O ₄ , a transition metal oxide 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 and 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 exhibit a relatively low safety and a high 1-phase reaction with high slope during charging and discharging. .

On the other hand, among the materials showing a two-phase reaction, the material has an excellent safety due to its structural stability and an excellent output characteristic according to a charging / discharging period. However, since the true density and the voltage are low, Low materials are present. In order to improve such a low electrical conductivity, when the carbon coating or the like is performed, the electrode density is lowered, so that the capacity of the battery is very low.

In this connection, in some prior arts, a mixture of a lithium nickel cobalt manganese composite oxide and a lithium manganese oxide is used as a cathode active material, or a mixture of a lithium composite oxide and a lithium cobalt oxide having a layered crystal structure is used Thereby producing a positive electrode active material. However, it has been confirmed that the effect of complementing the physical properties of the cathode active material prepared by mixing different oxides is not great.

Further, when a lithium composite oxide having a layered crystal structure and a lithium iron phosphate are mixed and used 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 whole of the active material .

Therefore, there is a high need for techniques to solve 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.

The inventors of the present application have conducted intensive research and various experiments, and have found that a specific electrode active material exhibiting a one-phase reaction during discharge and a specific electrode exhibiting a lower voltage than that of a two- The composite electrode has been developed in which the active material is applied to the respective current collectors to form individual electrodes. Such a composite electrode has been confirmed that safety and low-temperature output characteristics can be improved while minimizing an increase in resistance due to simple mixing of the active material And completed the present invention.

Accordingly, the composite electrode according to the present invention comprises a first electrode having one or more electrode active materials selected from the following formula (1) and exhibiting a one-phase reaction during the discharge process, the first electrode being coated on the first current collector, And a second electrode having a second current collector coated thereon with one or more electrode active materials selected from the following formula (2), wherein the second electrode has a lower voltage than the first electrode.

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 at least one transition metal selected from one period transition metal;

M 'is at least one 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 a metal and a metalloid having a one-cycle transition metal and a structure stable to 6 coordination;

A is selected from a stable metal and a quasi metal in a four coordination structure.

As described above, when the active material is simply mixed and used, the properties of the mixture, rather than the optimum characteristics of the active material, are exerted. Therefore, the effect of complementing the physical properties due to mixing is not significant, and resistance is increased.

On the contrary, since the composite electrode according to the present invention is composed of different kinds of electrodes coated with different kinds of active materials, not only the characteristics of each of the active materials can be maximized, but also the power the deterioration of the power characteristics can be minimized.

Specifically, since the active materials having different specific characteristics are coated on the electrode current collectors to form different types of electrodes, they complement each other not only in terms of physical properties but also exhibit synergistic effects due to other electrode active materials having the same physical properties So that the characteristics of each of the active materials can be maximized as compared with the case where the active materials are simply mixed and used.

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

The compound of Formula 1 or Formula 2 according to the present invention may preferably be a lithium transition metal oxide or lithium iron phosphate of 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 is a lithium The transition metal oxide serves as a separation layer of the transition metal oxide, so that the safety of the battery can be further enhanced.

The positive electrode active material may be Li _x (Ni _v Mn _w Co _y M _z ) O _{2 - t} A _t 0.9, 0? Z? 0.9, x + v + w + y + z = 2, 0? T <0.9, 0? W? 0.9, 0? W? 0.9, 0.2, M is +2 or +4 is one or more metal or transition metal cation of oxidation number, A is -1 or -2 valent anion), Li _a Mn _2-b M ' _b O _4-c A' _c Wherein M 'is at least one metal or transition metal cation of an oxidation number of +2 to +4, A' is -1 or - A divalent anion), a disulfide compound, Fe ₂ (MoO ₄ ) ₃ , and the like, but is not limited thereto.

INDUSTRIAL APPLICABILITY As described above, the composite electrode according to the present invention can minimize an increase in resistance due to simple mixing of electrode active materials, and can improve safety. Such a composite electrode exhibits excellent low temperature output characteristics Can be used for the production of lithium secondary batteries.

The positive electrode active material according to the present invention may optionally comprise 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 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 positive electrode for a secondary battery can be produced, for example, by applying a slurry prepared by mixing the positive electrode material mixture with a solvent such as NMP, onto a 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.

In the composite electrode according to the present invention, the negative electrode active material is a carbon-based anode active material, titanium-containing _{oxides, 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, Group 2 or Group 3 elements of the periodic table, ? Y? 3; 1? Z? 8); 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, but are not limited thereto.

Such an anode active material, if necessary, constitutes the anode mixture including the components as described above.

The negative electrode for a secondary battery can be produced, for example, by applying a slurry prepared by mixing the negative electrode mixture to a solvent such as NMP, coating the negative electrode collector, followed by drying and rolling.

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

The porous separation membrane prevents short-circuiting 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 electrode assembly for a secondary battery according to the present invention may be manufactured in various forms such as a jelly-roll type, a stack type, a stack / folding type, or a stack / zigzag folding type. A cylindrical can, a square can, or 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 can be preferably a lithium secondary battery, and is particularly applicable to a so-called lithium ion polymer battery in which a lithium-containing non-aqueous electrolyte is impregnated with an 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.

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 lithium secondary battery according to the present invention can be used not only for a battery cell used as a power source for a small device but also for a middle- or large-sized battery module including a plurality of battery cells used as a power source for a medium- Can be preferably used. Further, it is preferably used for a middle- or large-sized battery module requiring high-rate characteristics, power characteristics, and the like depending on operating conditions and requiring 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); An electric golf cart; Power storage devices, 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 (7)

A first electrode having one or more electrode active materials represented by the following formula (1) and exhibiting a one-phase reaction during the discharge process, the first electrode being coated on the first current collector; and a two-phase reaction A second electrode having a second current collector coated with one or more electrode active materials selected from the following formula (2) And
And a porous separator interposed between the composite electrodes. The electrode assembly for a secondary battery according to claim 1,
Li (Li _x M _1-x ) O ₂ (1)
In this formula,
0? X <0.5; And M is one selected from the group consisting of Ni, Co and Mn;
(1-z) LiFe _x P _1-x O ₄ * zC (2)
In this formula,
0? X <0.5 and 0? Z <0.1 delete A lithium secondary battery comprising the electrode assembly according to claim 1. A battery module comprising the lithium secondary battery according to claim 3 as a unit cell. An electric vehicle characterized by using the battery module according to claim 4 as a power source. The power storage device according to claim 4, wherein the battery module is used as a power source. A hybrid electric vehicle characterized by using the battery module according to claim 4 as a power source.