KR20080015162A - Positive electrode coated with conductive polymer in uniform pattern and secondary battery containing the same - Google Patents

Abstract

A positive electrode is provided to enhance an adhesion of an electrode mixture to a current collector in conductive polymer-coated portions and to improve electroconductivity between the current collector and electrode mixture in conductive polymer-uncoated portions. A positive electrode(100) has a positive electrode mixture coating layer on a current collector(110), wherein the positive electrode mixture comprises a positive electrode active material, a binder, and a conductive material. To improve an adhesion of the positive electrode mixture to the current collector and electroconductivity, the positive electrode is prepared by coating the current collector with a conductive polymer(130) thinly in a uniform pattern, and then coating the pattern coating layer with the positive electrode mixture(140).

Description

Positive Electrode Coated with Conductive Polymer in Uniform Pattern and Secondary Battery Containing the Same}

1 is a schematic diagram of a manufacturing process for forming a polymer layer and a mixture layer in the positive electrode according to an embodiment of the present invention;

2A-2C are plan views of release paper that may be used illustratively in the anode of FIG. 1.

The present invention relates to a positive electrode in which a conductive polymer is coated in a uniform pattern. More specifically, the present invention relates to a positive electrode, in which a positive electrode mixture composed of a positive electrode active material, a binder, and a conductive material is applied onto a current collector and is in close contact with the current collector. To improve the bonding strength and electrical conductivity of the positive electrode mixture to the current collector, the secondary polymer, characterized in that the thin coating of the conductive polymer in a uniform pattern on the current collector, and is prepared by applying a positive electrode mixture on the pattern coating layer Provided is a battery positive electrode and a secondary battery comprising such a positive electrode.

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.

In general, in a lithium secondary battery, a mixture of a conductive material and a binder mixed with a lithium cobalt oxide, a lithium nickel oxide, a lithium manganese oxide, or the like as a positive electrode active material is applied to a current collector such as aluminum and nickel, and then pressurized. The positive electrode manufactured by making it is used.

However, in the positive electrode having the above structure, due to the volume change during repeated charging and discharging of the battery, a problem occurs that the mixture adhering to the surface of the current collector is peeled off. This peeling phenomenon is one of the main causes of deterioration of battery performance and safety. In particular, the adhesion between the current collector and the mixture mainly depends on the binder contained in the mixture, and PVdF, which is generally used as the binder, exhibits adhesive force by physical bonding, thereby solving the problem of weak binding strength of the binder. There is a need for a solution.

As a method for solving this problem, for example, there is a method of increasing the bonding strength with the mixture by etching the surface of the aluminum current collector to form fine irregularities. This method has an advantage that an aluminum current collector having a high specific surface area can be obtained by a simple process, but has a problem in that the life of the aluminum current collector is reduced due to the etching process.

As another method, Korean Patent No. 0362281 and Korean Patent No. 0573098 disclose a method of improving a bonding force with an electrode mixture by coating a conductive polymer on the surface of a current collector. However, the conductive polymer has the advantage of improving the bonding strength between the current collector and the electrode mixture, but has a disadvantage of lowering the electrical conductivity between the current collector and the electrode mixture. That is, when the conductive polymer is coated between the current collector and the electrode mixture, the electrical conductivity between the current collector and the mixture is reduced than when the current collector and the mixture are in direct contact. In particular, when the conductive polymer is applied to the entire surface of the current collector as in the above technique, the degree of decrease in electrical conductivity becomes more serious.

Therefore, there is a high demand for a technology capable of improving the bonding strength without compromising the electrical conductivity between the current collector and the mixture.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application have applied a conductive polymer on the current collector in a positive electrode mixture coated on a current collector comprising a positive electrode active material, a binder, and a conductive material. When the coating is thin in a uniform pattern and the positive electrode mixture is applied on the coating layer, it is found that the bonding strength of the positive electrode mixture to the current collector can be improved while maintaining the electrical conductivity between the current collector and the mixture. Came to complete.

Accordingly, the positive electrode according to the present invention is a positive electrode in a state in which a positive electrode mixture composed of a positive electrode active material, a binder, and a conductive material is adhered to a current collector and is in close contact with each other. In order to improve, the conductive polymer is thinly coated in a uniform pattern on a current collector, and is prepared by applying a positive electrode mixture on the pattern coating layer.

That is, the positive electrode according to the present invention can increase the bonding strength of the electrode mixture to the current collector in the portion where the conductive polymer is coated, and improve the electrical conductivity between the current collector and the electrode mixture in the portion where the conductive polymer is not coated. It has the advantage of being able to.

The conductive polymer is not particularly limited as long as it is a polymer having electrical conductivity, and may be various. Preferably, the conductive polymer may be one or two or more selected from the group consisting of polyacetylene, polypyrrole, polyaniline, and polythiophene.

The pattern coating layer of the conductive polymer is preferably 0.5 to 100 μm so as to stably maintain the bond between the current collector and the positive electrode mixture and to suppress the decrease in the electric conductivity as much as possible and not adversely affect the overall volume of the finished battery. It may be formed with an area of 20 to 80% of the thickness and current collector area. In other words, if the thickness of the pattern coating layer is too thin or the coating area is too small, and it is difficult to expect the improvement of adhesion due to the formation of the conductive polymer layer, on the contrary, if the pattern coating layer is too thick or the coating area is large, the width of the internal resistance increase is increased. May degrade performance.

In one preferred example, the pattern coating layer may be formed by applying a mixture containing a conductive polymer on the current collector and then drying. At this time, the coating method of the pattern coating layer is not particularly limited and may be various, for example, a spray coating method, sputtering and the like. In addition to the conductive polymer, the mixture may include a surfactant or the like such that the conductive polymer can be easily adhered to the surface of the current collector, and the conductive polymer and the surfactant may be, for example, in a solution such as NMP. It can be prepared by melting.

In another preferred example, the pattern coating layer may be formed by putting a current collector in a mixture including a monomer for forming a conductive polymer and an initiator, the conductive polymer is synthesized by the polymerization of the monomer on the current collector. In this case, in order to speed up the synthesis rate of the conductive polymer, a current may be applied to the current collector. More specifically, a mixture containing the monomer for forming the conductive polymer and the initiator is used as an electrolyte, and for example, an electrochemical cell for synthesizing the conductive polymer is prepared by using an aluminum current collector and platinum as the counter electrode. By applying a current to the aluminum current collector and the platinum electrode, the conductive polymer can be electrochemically synthesized. That is, the monomer of the conductive polymer may be anodized polarized by an applied current, and may be coated with the conductive polymer on the surface of the current collector. As in the above-described example, the mixture may include a surfactant and the like so that the conductive polymer can be easily adhered to the surface of the current collector, and the monomer and initiator for forming the conductive polymer, and the surfactant, for example For example, it may be prepared by dissolving in a solution such as NMP.

In the above example, the monomer is not particularly limited as long as it can synthesize the conductive polymer by a polymerization reaction, and may vary. Preferably, in the group consisting of acetylene monomer, pyrrole monomer, aniline monomer, and thiophene monomer It may be one or more than one selected.

In the present invention, release paper may be used to thinly coat the conductive polymer in a uniform pattern, and the type of such release paper may be varied, for example, stripes (FIG. 2A), islands (FIG. 2B), Or honeycomb patterns (FIG. 2C). An exemplary method of patterning a conductive polymer using the release paper can be more easily confirmed in FIG. 1, in which a manufacturing process of a positive electrode is schematically illustrated.

Referring to FIG. 1, the positive electrode 100 e is coated and dried with a mixture 130 containing a conductive polymer in a state in which a release paper 120 is attached on an aluminum current collector 110 a. And (c) removing the release paper 120 and then applying the positive electrode mixture 140 including the positive electrode active material, the binder, and the conductive material (e).

Although the above example has been described as applying the conductive polymer to the aluminum current collector attached to the release paper, as in the above example, it is possible to form a pattern coating layer using the aluminum current collector with release paper in the polymerization reaction system of the conductive polymer. Of course it can.

Examples of the positive electrode active material include a layered compound such as lithium cobalt oxide (LiCoO ₂ ) and 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 M _x O 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.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 5 to 30 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material 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. Specific examples of commercially available conducting agents include acetylene black Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack, EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

In the present invention, a filler may be further added to the positive electrode mixture as needed. Such a filler is optionally used as a component for inhibiting the 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 thereof include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The positive electrode mixture may be added to a solvent such as NMP, prepared as a slurry, and then coated on a current collector coated with a conductive polymer, followed by drying and compression to prepare a positive electrode.

The current collector for the positive electrode is generally made to a thickness of 3 to 500 ㎛. 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.

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

The lithium secondary battery according to the present invention is composed of a positive electrode, a negative electrode, a separator, and a lithium salt-containing nonaqueous electrolyte prepared by the above method.

The negative electrode is manufactured by applying, drying, and compressing a negative electrode material on a current collector, and, as necessary, may further include components as described above.

The current collector for the cathode is generally made of a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, and aluminum-cadmium alloys may be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As said negative electrode material, For example, carbon, such as hardly graphitized carbon and graphite type 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': Al, B, P, Si, Group 1, 2, 3 of the periodic table) Metal composite oxides such as a group element, halogen, 0 <x ≦ 1, 1 ≦ y ≦ 3, 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.

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; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. 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, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

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, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

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.

In one preferred embodiment, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) _2, and the like, may be prepared by cyclic carbonate of EC or PC as a highly dielectric solvent and DEC, DMC or EMC as a low viscosity solvent. Lithium salt-containing non-aqueous electrolyte can be prepared by adding to a mixed solvent of linear carbonate.

Hereinafter, the present invention will be described in more detail based on the following examples, but the scope of the present invention is not limited thereto.

Example 1

1-1. Manufacture of anode

20% by weight polypyrrole and 0.5% by weight Pluronic ^™ F127 (BASF) as a surfactant were added to the NMP solution to prepare a mixture comprising the conductive polymer. A stripe release paper with a size of 40% of the current collector area was coated and dried on an aluminum foil to which the stripe release paper was regularly attached as shown in FIG. 2A, and then the release paper was removed. The conductive polymer was coated on the aluminum foil. Then, 94.5% by weight of LiCoO ₂ , 2.5% by weight of Super-P (conductor), and 2.5% by weight of PVDF (binder) were added to NMP (N-methyl-2-pyrrolidone) as a positive electrode active material for positive electrode mixture. After preparing the slurry, a positive electrode was prepared by coating, drying and pressing on an aluminum foil coated with a conductive polymer.

1-2. Preparation of Cathode

95% by weight of artificial graphite as a negative electrode active material, 2.5% by weight of Super-P (conductive material), and 2% by weight of PVDF (binder) were added to NMP as a solvent to prepare a slurry for negative electrode mixture, followed by coating on copper foil, The negative electrode was prepared by drying and pressing.

1-3. Preparation of Electrolyte

As the electrolyte, an EC / EMC solution containing a lithium salt of 1M LiPF ₆ was used.

1-4. Manufacture of batteries

A porous separator (Celgard ^TM ) was placed between the positive electrode and the negative electrode prepared in 1-1 and 1-2, respectively, and a non-aqueous electrolyte prepared in 1-3 was prepared to manufacture a lithium secondary battery.

Example 2

20% by weight of pyrrole monomer, 1.5% by weight of benzoylperoxide as initiator, and 0.5% by weight of Pluronic ^™ F127 (manufactured by BASF) as a surfactant were added to the NMP solution to prepare a mixture comprising a monomer for forming a conductive polymer. Applying a current of 0.5 Ma / cm ² in a state of immersing aluminum foil and platinum on which release paper is attached, and then removing the aluminum foil to remove the release paper, except that the conductive polymer was coated on the aluminum foil. Then, a positive electrode and a battery were manufactured in the same manner as in Example 1.

Comparative Example 1

A positive electrode and a battery were manufactured in the same manner as in Example 1, except that the positive electrode mixture was applied, dried, and compressed without directly coating the conductive polymer on the aluminum foil.

Comparative Example 2

After the conductive polymer was coated on the entire surface of the aluminum foil, a positive electrode and a battery were manufactured in the same manner as in Example 1, except that the positive electrode mixture was applied, dried, and compressed.

Experimental Example 1

In order to compare the bonding strength of the positive electrode mixture to the current collector in the positive electrode according to Examples 1 and 2 and Comparative Examples 1 and 2, each of the prepared positive electrode surface was cut to a fixed size and fixed on a slide glass, and then the copper foil was Peeling was measured 180 ° peeling strength, the results are shown in Table 1 below. The peeling strength is a value measured at a positive electrode separated from the battery by discharging and discharging the battery 50 times continuously according to Examples and Comparative Examples. At this time, the positive electrode is a state in which the electrolyte is completely removed.

TABLE 1

As shown in Table 1, the positive electrode of Examples 1 and 2 and Comparative Example 2 according to the present invention shows a higher electrode adhesion than the positive electrode of Comparative Example 1 is not coated with a conductive polymer. That is, it was found that the bonding strength of the positive electrode mixture to the current collector was improved by the conductive polymer.

Experimental Example 2

In order to compare the electrical conductivity between the current collector and the positive electrode mixture in the positive electrode according to Examples 1 and 2 and Comparative Examples 1 and 2, the resistance of the prepared positive electrode was measured, and the results are shown in Table 2 below.

TABLE 2

As a result, the anodes of Examples 1 and 2 according to the present invention had a higher internal resistance than Comparative Example 1, which did not include the conductive polymer coating layer, but the conductive polymer layer formed a patterned coating layer, Compared with the comparative example 2 which forms the coating layer in the front surface, it turns out that it has a much lower internal resistance.

As described above, the positive electrode according to the present invention has an effect of improving the bonding strength of the positive electrode mixture to the current collector while maintaining the electrical conductivity between the current collector and the mixture.

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 (10)

A positive electrode in a state in which a positive electrode mixture comprising a positive electrode active material, a binder, and a conductive material is adhered to the current collector and adhered to the current collector, so as to improve the binding strength and electrical conductivity of the positive electrode mixture to the current collector, Coating a conductive polymer thin in a uniform pattern, the positive electrode for a secondary battery, characterized in that is produced by applying a positive electrode mixture on the pattern coating layer. The positive electrode of claim 1, wherein the conductive polymer is at least one selected from the group consisting of polyacetylene, polypyrrole, polyaniline, and polythiophene. The positive electrode for secondary batteries of claim 1, wherein the pattern coating layer has a thickness of 0.5 to 100 μm. The cathode for a secondary battery of claim 1, wherein the pattern coating layer is coated with a coating area of 20 to 80% based on the area of the current collector. The cathode for a secondary battery of claim 1, wherein the pattern coating layer is formed by applying a mixture containing a conductive polymer onto a current collector on which a release paper is attached in a pattern shape, and then drying and removing the release paper. The method of claim 1, wherein the pattern coating layer is a mixture containing a monomer for forming a conductive polymer and an initiator, the current collector is attached to the release paper in a pattern shape, and the conductive polymer is synthesized by the polymerization reaction of the monomer on the current collector After that, the secondary battery positive electrode, characterized in that formed by removing the release paper. The positive electrode of claim 6, wherein the monomer is one or two or more selected from the group consisting of an acetylene monomer, a pyrrole monomer, an aniline monomer, and a thiophene monomer. The cathode of claim 1, wherein the cathode active material is lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium manganese-cobalt-nickel oxide, or a combination of two or more thereof. A secondary battery comprising the positive electrode according to any one of claims 1 to 8. The secondary battery of claim 9, wherein the battery is a lithium secondary battery.

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