KR20090076276A - Cathode for battery, method for manufacturing thereof, and lithium secondary battery comprising the same - Google Patents

Abstract

A positive electrode is provided to enable the deposition of a conductive material having various structures and properties, to control the thickness of a deposition layer, and to improve conductivity while showing excellent storage ability at a high temperature. A positive electrode comprises a positive active material and a conductive material layer on a part or the whole of a positive electrode mixture. The conductive material is at least one selected from the group consisting of conductive polymer, conductive metal and oxides of the conductive metal. The conductive polymer is at least one selected from the group consisting of polypyrrole, polythiophene, polyaniline, polyacetylene, polysulfurnitride, polyphenylene, and combinations thereof.

Description

A cathode, a method of manufacturing the same, and a lithium secondary battery comprising the same

The present invention relates to a positive electrode having a positive electrode mixture applied to a positive electrode current collector used in a lithium secondary battery, and then coated with a conductive material layer by CVD deposition, a method for manufacturing the same, and a lithium secondary battery including the same. The conductive material layer may be formed on the coated positive electrode current collector to increase conductivity and improve storage performance at high temperature.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and discharge voltage. It is used. Among them, lithium secondary batteries are the most used batteries due to their excellent electrode life and high fast charge and discharge efficiency.

However, the lithium secondary battery has a problem in that the reaction between the lithium transition metal oxide, which is a cathode active material, and the electrolyte is accelerated at a high temperature, thereby generating a by-product that increases the resistance of the cathode, thereby rapidly decreasing the shelf life at a high temperature. As a method for solving this problem, some prior arts propose a method of adding a substance which decomposes at a high temperature to form a protective film on the positive electrode to the electrolyte, but this method can reduce the capacity and output of the battery and The addition of a separate material has a problem that is likely to cause a decrease in battery performance.

As another method, some prior arts suggest a method of coating a cathode active material with a conductive material to lower the contact interface resistance between the cathode active material and the electrolyte or by-products generated at high temperatures. As an example, a method of coating a conductive polymer on a cathode active material is known. In general, however, conductive polymers exhibit poor solubility in organic solvents. Therefore, in order to manufacture the positive electrode, a lithium transition metal oxide, a conductive agent, a binder, and the like are mixed with an organic solvent such as NMP to make a slurry, and it is difficult to apply the same to the process of manufacturing the positive electrode by attaching it to an electrode plate such as aluminum.

In order to solve this problem, some prior art proposes a method of inducing a polymerization reaction on the surface of the oxide by dissolving the conductive polymer monomer in an organic solvent and then acting as a catalyst of a lithium transition metal oxide as a cathode active material and have. According to this method, the reaction system is acidified in order to induce a polymerization reaction on the particle surface of the lithium transition metal oxide. Such acidification has a problem of degrading the performance of the positive electrode active material. Moreover, such a polymerization reaction makes it difficult to obtain a homogeneous coating of the particle surface.

Therefore, the present invention is to solve the conventional problem that the reaction between the positive electrode active material and the electrolyte of the lithium secondary battery is promoted at a high temperature to generate a by-product that increases the resistance of the positive electrode, the storage life at a high temperature is sharply reduced as described above. .

Thus, the present invention was able to solve the above problems by applying a positive electrode mixture including a positive electrode active material, a conductive material, and a binder to the positive electrode current collector, and then coating the positive electrode mixture using a CVD deposition method.

Accordingly, an object of the present invention is to provide a positive electrode of a lithium secondary battery having excellent high temperature storage capability and improved conductivity.

In addition, another object of the present invention is to provide a method for producing a positive electrode having the above characteristics.

Still another object of the present invention is to provide a lithium secondary battery including the positive electrode.

By coating the conductive material on the current collector coated with the positive electrode mixture using the chemical vapor deposition method as described in the present invention, it is possible to deposit conductive materials having various structures and properties, and also to manufacture a positive electrode whose thickness can be easily controlled. When applied to the secondary battery, it can improve conductivity while showing excellent shelf life even at high temperatures.

The positive electrode of the present invention for achieving the above object is characterized in that it comprises a positive electrode mixture applied to the current collector, and a conductive material layer in part or all of the positive electrode mixture.

In addition, a method of manufacturing a positive electrode for achieving another object of the present invention comprises the steps of applying a positive electrode mixture on the current collector; And applying a conductive material layer to at least a portion of the positive electrode mixture.

In addition, the present invention is characterized by providing a lithium secondary battery comprising a positive electrode having the above characteristics in order to achieve another object.

Hereinafter, the present invention will be described in more detail.

The positive electrode of the present invention is a coating of a positive electrode mixture on a current collector, and then includes a conductive material layer thereon.

The positive electrode is prepared by applying the slurry of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector, followed by drying, and optionally, a filler is further added to the mixture. The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used.

The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Specific examples of the positive electrode active material of the present invention include a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 - x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _{1- x} MxO ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _{2 - x} M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein 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 alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these. Preferably, the positive electrode active material may be lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium manganese-cobalt-nickel oxide, or a combination of two or more thereof.

The binder is a component that assists the bonding of the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the electrode mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Low ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers thereof, and the like.

The conductive material is a component for further improving the conductivity of the electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the electrode mixture. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder 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 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 fiber and carbon fiber, are used.

Meanwhile, the conductive material according to the present invention is selected from the group consisting of a conductive polymer, a conductive metal, and an equivalent conductive material, and any conductive material is not limited.

In the case of the conductive polymer, at least two selected from the group consisting of polypyrrole, polythiophene, polyaniline, polyacetylene, polysulfurtritride, polyphenylrin, and combinations of two or more thereof.

In addition, the conductive metal is Li, Al, Sn, Bi, Si, Sb, Ni, Cu, Ti, V, Cr, Mn, Fe, Co, Zn, Mo, W, Ag, Au, Pt, Ir, Ru and It is 1 or more types chosen from the group which consists of these alloys.

Hereinafter, a method of manufacturing a positive electrode according to the present invention will be described in detail.

First, a positive electrode mixture slurry including the positive electrode active material, the conductive material, the binder, and other additives is prepared on a metal current collector, and applied thereto. Application of the positive electrode mixture slurry is carried out by a method known in the art, and is not particularly limited.

Next, a positive electrode mixture is applied onto the positive electrode current collector, and then a conductive material layer is applied to at least a portion of the positive electrode mixture. The coating of the conductive material layer here uses chemical vapor deposition (CVD). The chemical vapor deposition method is advantageous because it has the following advantages in spite of the high reaction temperature, the complicated reaction path, and the disadvantage that most used gases are very dangerous substances.

First, it is easy to manufacture materials that are difficult to manufacture due to the high melting point. Second, high purity. Third, mass production is possible and the cost is lower than physical vapor deposition. This is because the deposition is possible and the control range of the process conditions is very wide, which makes it easy to obtain thin films of various characteristics and has good step coverage.

Chemical vapor deposition method having the same characteristics as described above A thermo-CVD method that is roughly classified into atmospheric pressure CVD reacted under atmospheric pressure and reduced pressure CVD and the like which have formed a film under reduced pressure (Q1-1Torr) to improve mass productivity and step coverage; Plasma-CVD which accelerates the reaction by electric energy under RF glow discharge to form a thin film, and does not require heat, thereby making it possible to lower the temperature; Irradiation of light forms a thin film by photochemical reaction, and unlike the plasma method, high energy charged particles or electric field are not involved in the reaction process, so that the damage in the laminated film is not taken into consideration, and a good film is formed. ; MO-CVD method capable of precise control of composition and characteristics of growth layer by thin film formation method using pyrolysis of organometallic compound; There is a laser CVD method that can selectively control the chemical reaction process by performing a selective reaction.

In the present invention, a variety of chemical vapor deposition methods listed above may be used, and among them, a low pressure CVD method among thermal-CVD methods is performed, and is carried out at a pressure of several tens of mTorr to several tens of torr and a condition of 200 to 500 ° C. It is preferable.

Raw material gas used in chemical vapor deposition It can be selected according to the type of thin film to be deposited. Generally, gas or solid raw material having a gas at room temperature or a sufficiently high vapor pressure is used to facilitate handling. If the vapor pressure is high, it is cooled, while if it is low, it is heated. Preferably, hydrides, halides and organometallic compounds are used.

In addition, the oxygen flow rate in the chemical vapor deposition method is 100 ~ 300 sccm (standard ㏄ / min), the flow rate of nitrogen (N) or argon (Ar) gas as a carrier gas is 50 ~ 250 sccm (standard ㏄ / min) It is preferable to set it as.

 Although the thickness of the conductive material layer applied by the chemical vapor deposition method as described above may be selectively varied, 0.1 to 100mm is preferred.

On the other hand, the present invention includes a secondary battery comprising a positive electrode prepared by applying a positive electrode mixture to the positive electrode current collector as described above, the negative electrode produced by coating and drying the negative electrode material on the negative electrode current collector, and a separator There are also features to provide.

The negative electrode of the present invention is a negative electrode active material, for example, carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, Ti which can be alloyed with lithium, and compounds containing these elements; Complexes of metals and compounds thereof with carbon and graphite materials; Lithium-containing nitrides, and the like, but are not limited thereto. Preferably, they are selected from the group consisting of crystalline carbon, amorphous carbon, silicon-based active material, tin-based active material, and silicon-carbon-based active material, alone or in combination of two or more. In addition, it may include a conventional binder, a conductive material, and other additives included in the negative electrode, and their specific examples and contents, etc. are usually sufficient to be added.

The lithium secondary battery of the present invention has a structure in which a lithium salt-containing non-aqueous electrolyte is impregnated in an electrode assembly having a separator interposed between a positive electrode and a negative electrode.

The separator 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 from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheet or nonwoven fabric made of glass fiber or polyethylene; Kraft paper or the like is used. Typical examples currently on the market include Celgard series (Celgard ^TM 2400, 2300 (manufactured by Hoechest Celanese Corp.), polypropylene separator (manufactured by Ube Industries Ltd. or Pall RAI), and polyethylene series (Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separator to increase the stability of the battery. Representative examples of such gel polymers include polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile and the like. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a nonaqueous electrolyte and a lithium salt. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, for example , Gamma-butylo lactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolon Aprotic organic solvents such as derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used. Can be.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating 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 good material to be dissolved 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-phenyl lithium borate, imide and the like can be used.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

Claims (16)

A positive electrode mixture applied to the current collector, and a positive electrode comprising a conductive material layer on part or all of the positive electrode mixture. The cathode of claim 1, wherein the conductive material is at least one selected from the group consisting of a conductive polymer, a conductive metal, and an oxide of a conductive metal. The method of claim 2, wherein the conductive polymer is at least one selected from the group consisting of polypyrrole, polythiophene, polyaniline, polyacetylene, polysulfurnitride, polyphenylene, and combinations of two or more thereof. anode. The method of claim 2, wherein the conductive metal is Li, Al, Sn, Bi, Si, Sb, Ni, Cu, Ti, V, Cr, Mn, Fe, Co, Zn, Mo, W, Ag, Au, Pt, At least one anode selected from the group consisting of Ir, Ru, and alloys thereof. Applying a positive electrode mixture on the current collector; A method of manufacturing a positive electrode comprising applying a conductive material layer to some or all of the positive electrode mixture. 6. The method of claim 5, wherein the cathode is one selected from the group consisting of the conductive polymer, the conductive metal and the oxide of the conductive metal. 7. The method of claim 6, wherein the polypyrrole, polythiophene, polyaniline, polyacetylene, polysulfuritride, polyphenylene, and at least one selected from the group consisting of two or more thereof. The method of claim 6, wherein the conductive metal is Li, Al, Sn, Bi, Si, Sb, Ni, Cu, Ti, V, Cr, Mn, Fe, Co, Zn, Mo, W, Ag, Au, Pt, A method for producing a positive electrode, characterized in that at least one selected from the group consisting of Ir, Ru, and alloys thereof. 6. The method of claim 5, wherein the coating of the conductive material layer uses chemical vapor deposition (CVD). The method of claim 9, wherein the chemical vapor deposition is performed at a temperature of 200 to 500 ° C. and a pressure of several tens of mTorr to several tens of torr. 10. The method of claim 9, wherein the chemical vapor deposition source gas is one selected from the group consisting of hydrides, halides, and organometallic compounds.  The method of claim 5, wherein the positive electrode mixture comprises a positive electrode active material, a conductive material, and a binder. The method of claim 12, wherein the positive electrode active material is a layered compound, or a compound substituted with one or more transition metals; Lithium manganese oxide represented by the formula Li _{1 + x} Mn _{2 - x} O ₄ , wherein x is 0 to 0.33; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxide; Ni-site type lithium nickel oxide represented by the formula LiNi _{1- x} MxO ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _{2 -x} M _x O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta, and x = 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 alkaline earth metal ions; Disulfide compounds; And Fe ₂ (MoO ₄ ) ₃ . The method of claim 12, wherein the conductive material is at least one selected from the group consisting of graphite, carbon black, conductive fibers, metal powder, conductive whiskey, conductive metal oxide, and polyphenylene derivatives. The method of claim 12, wherein the binder is polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone , Tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof. The manufacturing method of the positive electrode made by gong. Lithium secondary battery comprising a positive electrode according to any one of claims 1 to 4.