KR20130117006A - Cathode slurry comprising novel binder and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: Anode slurry is provided to increase the lifespan characteristic and output property of a battery by improving the delamination of electrode. CONSTITUTION: Anode slurry is a cathode active material for a secondary battery. The anode slurry is made by mixing an anode material comprising the spinel-structured lithium manganese group oxide represented by the chemical formula 1: LixMyMn2-yO4-zAz, a conductive material, and a binder with organic solvent. The binder comprises a material in which at least two functional groups having different reactivity are combined with inorganic metal. In the chemical formula 1, 0<=x<=0.1; 0<y<=0.5; and 0<=z<=0.2. M is a transition metal cation having divalent oxidation number. A is a monovalent or divalent anion.

Description

Anode Slurry Comprising Novel Binder and Lithium Secondary Battery Comprising the Same

The present invention relates to a positive electrode slurry comprising a novel binder and a lithium secondary battery including the same, and more particularly, a spinel structure lithium represented by the following Chemical Formula 1 as a positive electrode active material for secondary batteries that occludes and desorbs lithium ions: A cathode slurry in which a cathode material including a manganese oxide, a conductive material, and a binder is mixed with an organic solvent, wherein the binder includes a material (binder) in which at least two kinds of different functional groups are bonded to an inorganic metal. It relates to a positive electrode slurry and a lithium secondary battery comprising the same.

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0 ≦ x ≦ 0.1; 0 <y ≦ 0.5; 0 ≦ z ≦ 0.2; M is a transition metal cation having an oxidation number of +2; A is an anion of oxidation number -1 or -2.

The increase in the price of energy sources due to the depletion of fossil fuels, the increase of interest in environmental pollution, and the demand for environmentally friendly alternative energy sources are becoming indispensable factors for future life. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, in the case of a lithium secondary battery, the demand for an energy source is rapidly increasing due to an increase in technology development and demand for a mobile device. Recently, the use of a lithium secondary battery as a power source for an electric vehicle (EV) and a hybrid electric vehicle , And the area of use is also expanding for applications such as power assisted power supply through gridization.

Conventional lithium ion secondary batteries generally use lithium-containing cobalt oxides such as LiCoO ₂ in a layered structure for the positive electrode, but lithium-containing nickel oxides and spinel crystals such as LiNiO _{2 in a} layered crystal structure. The use of lithium-containing manganese oxides such as LiMn ₂ O _{4 in} structure is also contemplated.

The lithium-containing manganese oxide of the spinel crystal structure has a problem of requiring a larger amount of binder than a cathode active material such as a lithium-containing cobalt oxide due to the large surface area.

The adhesion of the electrode affects the electrode processability and the stability of the electrode performance.

Inadequate adhesion force induces electrode peeling phenomenon in electrode drying, pressing, etc., and improves the electrode defect rate. In addition, peeling of an electrode with low adhesive force even by an external impact of the battery can adversely affect stability such as battery life characteristics. Such electrode peeling increases the contact resistance between the electrode material and the current collector, do.

However, when the binder ratio is increased to solve the adhesive force problem, there is a problem in that the binder acts as a resistance element in the electrode as well as a disadvantage that the active material ratio is reduced, thereby decreasing the performance.

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.

Accordingly, an object of the present invention is to include a positive electrode slurry and a lithium secondary battery including the same to improve the lifespan and output characteristics of a battery by improving a peeling phenomenon of an electrode including a material capable of simultaneously bonding with an electrode current collector and an organic compound. To provide.

Therefore, the positive electrode slurry according to the present invention is a positive electrode active material for storing and detaching lithium ions, and a positive electrode material containing a lithium manganese oxide, a conductive material, and a binder having a spinel structure represented by the following Chemical Formula 1 in an organic solvent: As one positive electrode slurry, the binder is characterized in that it comprises a substance (binder) in which at least two kinds of different functional groups are bonded to an inorganic metal.

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

Wherein 0 ≦ x ≦ 0.1; 0 <y ≦ 0.5; 0 ≦ z ≦ 0.2; M is a transition metal cation having an oxidation number of +2; A is an anion of oxidation number -1 or -2.

Wherein 0 ≦ x ≦ 0.1; 0 <y ≦ 0.5; 0 ≦ z ≦ 0.2; M is a transition metal cation having an oxidation number of +2; A is an anion of oxidation number -1 or -2.

The spinel-structure lithium manganese oxide represented by Chemical Formula 1 is a part of manganese (Mn) that is substituted with a transition metal cation having an oxidation number of +2, and in a specific embodiment of the present invention, M is nickel (Ni) And the maximum substitution amount of nickel may be 0.5 mol%. In this case, the lithium manganese oxide represented by Chemical Formula 1 is LiNi _0.5 Mn _1.5 O ₄ .

Meanwhile, in Chemical Formula 1, the oxygen element may be partially substituted with an anion of -1 or -divalent oxidation number, and the maximum substitution amount may be less than 0.2 mol%. In a specific embodiment of the present invention, the anion is F, Cl It may be at least one anion selected from the group consisting of halogen, such as Br, I, S and N.

By substituting these anions, the binding force with the transition metal is improved and the structural transition of the compound is prevented, so that the lifetime of the battery can be improved. On the other hand, if the amount of substitution of the anion A is too large (t ≧ 0.2), it is not preferable because the life characteristics are lowered due to the incomplete crystal structure.

The lithium manganese oxide may further include cathode active materials other than the cathode active material represented by Formula 1 above. That is, the lithium manganese oxide may be included in more than 50% by weight to 100% by weight relative to the total weight of the positive electrode active material.

When the content of the lithium manganese oxide is 100% by weight based on the total weight of the positive electrode active material, it means a case in which the positive electrode active material is composed of only lithium manganese oxide.

The content of the binder or the binder may be 0.1 to 10% by weight based on the total weight of the cathode material.

When the content of the binder is less than 0.1% by weight based on the total weight of the positive electrode material, the binding force between the desired positive electrode current collector and the positive electrode active materials cannot be expected, and when the content of the binder is 10% by weight or more, it is not preferable because it acts as a resistance element.

Therefore, for the above reason, the content of the binder is more preferably 0.1 wt% or more and 5 wt% or less.

The inorganic metal may be one or two or more selected from the group consisting of silane (Si), titanium (Ti), zinc (Zn), and chromium (Cr), and the binder may be a proton present on the surface of the organic compound. It is preferable to include the functional group -OR (R is H or an alkyl group) which reacts with (H ⁺ ).

The organic compound may be, for example, carbon black, calcium carbonate, graphite, aramid or fiber.

The present invention also provides a cathode current collector comprising a cathode coated with the cathode slurry and a lithium secondary battery comprising the cathode and the anode, and a cathode slurry including an anode active material represented by the following Formula 2 It provides a lithium secondary battery comprising a negative electrode applied to.

Li _x Ti _y O ₄ (0.5≤x≤3; 1≤y≤2.5) (2)

For example, the negative electrode active material represented by Chemical Formula 2 may be Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O _4, or the like. It is not limited only to these.

More preferably, Li _1.33 Ti _1.67 O ₄ , which has a spinel structure with little change in crystal structure and excellent reversibility during charge and discharge, may be used.

The method for producing lithium titanium oxide represented by Chemical Formula 2 is well known in the art, for example, lithium and a lithium salt in a solution in which lithium salts such as lithium hydroxide, lithium oxide, lithium carbonate and the like are dissolved in water. According to the atomic ratio of titanium, titanium oxide or the like is added as a titanium source, followed by stirring and drying to prepare a precursor and then firing it.

In the negative electrode slurry, the binder is preferably contained in an amount of 0.1 wt% to 10 wt%, based on the total weight of the negative electrode material.

The lithium 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.

Also, the present invention provides a battery pack including the battery module as a power source of a middle- or large-sized device, wherein the middle- or large-sized device is an electric vehicle (EV), a hybrid electric vehicle (HEV) An electric vehicle including a plug-in hybrid electric vehicle (PHEV), a power storage device, and the like, but the present invention is not limited thereto.

The structure of the battery module and the battery pack and the method of manufacturing the battery module and the battery pack are well known in the art, so a detailed description thereof will be omitted herein.

As described above, as described above, the positive electrode slurry according to the present invention contains a substance containing two kinds of different functional groups as a binder in the molecule as described above, thereby improving processability and mechanical properties of the electrode. The effect of improving the stability of the battery through improvement.

In addition, the ratio of the active material is increased by decreasing the ratio of the binder and the resistance element is reduced by the binder, thereby improving the performance of the battery.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

In addition to the lithium manganese oxide of Chemical Formula 1, the positive electrode active material according to the present invention may further include other lithium-containing transition metal oxides.

Examples of the other lithium-containing transition metal oxides include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta and y = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The positive electrode may be prepared by applying a slurry prepared by mixing a positive electrode mixture containing the positive electrode active material with a solvent such as NMP, coating the positive electrode collector, followed by drying and rolling.

In addition to the cathode active material, the cathode mixture may optionally include a conductive material, a binder, a filler, and the like.

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, and examples thereof include copper, stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. The positive electrode current collector may be formed into various shapes such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, or the like by forming fine irregularities on the surface to enhance the bonding force of the positive electrode active material.

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 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.

Typical examples of the dispersion include isopropyl alcohol, N-methyl pyrrolidone (NMP), and acetone.

The method of evenly applying the paste of the electrode material to the metal material can be selected from known methods or performed by a new suitable method in consideration of the properties of the material. For example, the paste can be uniformly dispersed by using a doctor blade or the like after being distributed on the current collector. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. In addition, a die casting method, a comma coating method, a screen printing method, or the like may be used. Alternatively, the resin may be formed on a separate substrate, and then pressed or laminated by a pressing or laminating method. .

Drying of the paste applied on the metal plate is preferably dried within one day in a vacuum oven at 50 to 200 ℃.

The negative electrode may be formed by coating a negative electrode active material on a negative electrode collector and drying the negative electrode active material. If necessary, the negative electrode may further include components such as a conductive agent, a binder, and a filler as described above.

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 conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, 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, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, and the like.

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; Kraft paper and the like are used. Representative examples currently on the market include the Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation membrane to increase the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

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 non-aqueous electrolyte is composed of a nonaqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane A non-protonic organic solvent such as an ether, a methyl pyrophosphate, or an ethyl propionate is used as the solvent, a sulfone, a methyl sulfolane, a 1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, .

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, Polymers containing ionic dissociation groups, and the like can 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 3 Li, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

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.

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 (15)

As a cathode active material for secondary batteries that occludes and desorbs lithium ions, a cathode slurry including a lithium manganese oxide having a spinel structure represented by Formula 1 below, a conductive material, and a binder, mixed with an organic solvent, and the binder is an inorganic metal. A cathode slurry comprising a substance (binder) in which at least two kinds of reactive groups with different reactivity are bonded.
Li _x M _y Mn _{2 - y} O _{4 - z z} (1)
Wherein 0 ≦ x ≦ 0.1; 0 <y ≦ 0.5; 0 ≦ z ≦ 0.2; M is a transition metal cation having an oxidation number of +2; A is an anion of oxidation number -1 or -2. The positive electrode slurry according to claim 1, wherein the inorganic metal is one or two or more selected from the group consisting of silane (Si), titanium (Ti), zinc (Zn), and chromium (Cr). The cathode slurry of claim 1, wherein the binder or binder is present in an amount of 0.1 to 10 wt% based on the total weight of the cathode material. The positive electrode slurry according to claim 1, wherein the binder comprises a functional group -OR (R is H or an alkyl group) which reacts with protons (H ⁺ ) present on the surface of the organic compound. The cathode slurry of claim 1, wherein M is Ni. The cathode slurry of claim 1, wherein A is at least one selected from the group consisting of halogen, such as F, Cl, Br, and I, and S and N. The cathode slurry of claim 1, wherein the lithium manganese oxide is LiNi _0.5 Mn _1.5 O ₄ . The cathode slurry of claim 1, wherein the lithium titanium oxide is contained in an amount of 50 wt% or more and 100 wt% or less based on the total weight of the positive electrode active material. The positive electrode in which the positive electrode slurry in any one of Claims 1-8 is apply | coated to the positive electrode electrical power collector. A lithium secondary battery comprising the positive electrode and the negative electrode according to claim 9. The lithium secondary battery according to claim 10, wherein the negative electrode is coated with a negative electrode slurry including a negative electrode active material represented by Formula 2 below.
Li _x Ti _y O ₄ (0.5≤x≤3; 1≤y≤2.5) (2) 12. The lithium secondary battery of claim 11, wherein the negative electrode slurry contains 0.1 to 10% by weight of a material (binder) in which at least two kinds of different functional groups are bonded to an inorganic metal, based on the total weight of the negative electrode material. . A battery module comprising the lithium secondary battery according to claim 10 as a unit cell. A battery pack comprising the battery module according to claim 13. A device comprising the battery pack according to claim 14 as a power source.