KR101466397B1 - Anode for lithium secondary battery, method for manufacturing thereof, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a negative electrode of a lithium secondary battery comprising a negative electrode active material particle coated on the negative electrode collector with a reduced amount of copper metal adsorbed thereon, a method for producing the same, and a lithium secondary battery including the negative electrode.

The present invention reduces the copper ions between the anode active material particles and adsorbs the copper ions, thereby making the copper metal serve as a conductive material, thereby allowing the reduced copper metal to be adsorbed on the minute voids between the active materials, Can be improved.

Cathode electrode * copper * reduction * lithium secondary battery * electronic conductivity

Description

[0001] The present invention relates to a negative electrode of a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the negative electrode,

The present invention relates to a cathode electrode used in a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the cathode electrode.

Unlike conventional primary batteries, which can not be charged, secondary batteries capable of charging and discharging are under active research in the development of advanced fields such as digital cameras, cellular phones, notebook computers, and hybrid vehicles. Examples of the secondary battery include a nickel-cadmium battery, a nickel-metal hydride battery, a nickel-hydrogen battery, and a lithium secondary battery. Among them, the lithium secondary battery is used as a power source of a portable electronic device at an operating voltage of 3.6 V or more, or several series are connected in series to be used in a high-output hybrid vehicle. Compared with a nickel-cadmium battery or a nickel-metal hydride battery The operating voltage is three times higher and the energy density per unit weight is also excellent.

However, since the lithium secondary battery has a high energy density, it is widely used as a power source for portable telephones, notebook computers, and digital cameras. However, it is inconvenient to frequently recharge the battery due to discharge during use due to limitations of the charging capacity. As the charging capacity of the secondary battery increases, the replacement cycle becomes longer, which makes the consumer more convenient.

Currently used lithium secondary batteries are composed of a cathode made of lithium-cobalt oxide powder, a cathode made of carbon, an organic electrolyte and a separator.

On the other hand, the anode uses graphite free of lithium ion migration as an anode active material, and uses graphite and carbon black having excellent conductivity as a conductive agent to improve the conductivity between the active materials, and the binder resin and the like are mixed to prepare a slurry. The slurry is coated on a copper foil as an electrode current collector to produce a negative electrode.

Examples of the carbon material that can be used as an anode material of a lithium ion battery include natural graphite, artificial graphite, graphitized mesocarbon microbeads, mesophase pitch-based carbon fibers, graphite such as graphite whiskers, various kinds of coke, Amorphous carbon materials such as mesocarbon microbeads, mesophase pitch carbon fibers, vapor grown carbon fibers, polyacrylonitrile carbon fibers, and thermosetting resin carbides.

When the graphite is used as an electrode material, it has an advantage of having a good potential flatness and a low potential, but it has a limitation of discharge capacity.

On the other hand, the amorphous carbon material has a relatively poor dislocation flatness, which makes it difficult to manufacture a large-capacity battery, but has a large discharge capacity and easy control of shape and physical properties.

Therefore, a method for compensating for the disadvantages of an anode material manufactured by only one kind of anode material by mixing two or more kinds of carbon materials is proposed. For example, JP-A-8-222206 and JP-B-7-326343 disclose such a method. However, the above method by simple mixing has a problem that it is difficult to obtain uniform characteristics.

In recent years, however, it is required to continuously improve performance such as higher capacity and cycle characteristics in order to cope with large capacity and frequent charging and discharging according to demand of large electric power by development and high function of information equipment. For this purpose, it is required to improve the conductivity in the electrode while maintaining the existing characteristics.

In order to improve the conductivity of the negative electrode, a material which is stable in the potential range in which the negative electrode operates and has excellent conductivity is used as a conductive agent. Graphite and carbon black are used as a conductive agent until now and they are physically contacted with the active material using a binder, To improve the movement.

On the other hand, lithium is charged and discharged by a reversible intercalation and deintercalation reaction between the layers of the carbon anode material. The theoretical charge / discharge capacity of a carbon material, which is a typical negative electrode material, is 372 mAh / g, but the actual charge / discharge capacity has a reversible charge / discharge capacity as low as about 200 to 320 mAh / g.

Therefore, in order to improve such a low charge / discharge capacity, a new anode material capable of replacing a carbon material has been studied.

Many new tin-based and silicon-based metal systems have been studied, and cobalt oxide-based oxides, silicon oxide-based oxides, and the like have been extensively studied. In the process of lithium ions entering and exiting the negative electrode material by repetitive charging and discharging,

Since the particles are gradually separated due to the expansion due to the change of the blood, the cycle characteristics are deteriorated and the application to the lithium secondary battery is actually limited. In recent years, attempts have been made to make nanoparticles to suppress such expansion and to increase the discharge capacity, but the cycle characteristics are not remarkably improved.

Recently, a carbon-doped carbon composite prepared by a method of mixing carbon particles capable of intercalating and deintercalating lithium ions with a compound containing copper ions and generating a copper oxide on the surface of all or a part of the carbon particles And a binder are used as a negative electrode material to provide a high capacity, high voltage lithium ion battery.

In addition, when copper is coated on the metal powder by an electroless plating or a liquid phase reduction method, it is used as a negative electrode material of a lithium secondary battery, and the cycle characteristics are somewhat improved but not significantly increased. The electroless plating or liquid phase reduction method is not preferable due to environmental waste solution, and impurities remaining in the plating solution and the reducing agent are likely to remain, and the concentration of oxygen in the powder is increased by introducing a powder washing process if necessary. In addition, there is a problem that the coupling between the coated copper and the powder is weak and the cycle characteristics are deteriorated easily.

Accordingly, in the present invention, as described above, various problems of the anode material of the lithium secondary battery are solved to improve the performance of the battery.

Accordingly, the present invention relates to a method for producing a cathode active material, which comprises immersing a cathode electrode coated with a carbonaceous anode active material on an anode current collector in an aqueous solution containing copper ions, As a result, a gap is formed between the negative electrode active material and the copper metal to increase the surface area of the current collector and improve the conductivity of the negative electrode active material, thereby solving the conventional problems as described above.

Accordingly, it is an object of the present invention to provide a negative electrode of a lithium secondary battery which improves the conductivity of the negative electrode active material and is excellent in the room temperature output and the low temperature output characteristic.

Another object of the present invention is to provide a method of manufacturing a negative electrode of a lithium secondary battery.

It is still another object of the present invention to provide a lithium secondary battery including a cathode electrode having the above-described characteristics.

The cathode electrode coated with the carbonaceous anode active material is allowed to adsorb copper ions between the cathode active material particles and the cathode active material particles by giving a potential that the copper ions are reduced from the aqueous solution to copper, The room temperature output and the low temperature output can be improved.

The conventional electrode conductive agent is physically contacted with the active material through the binder. However, the present invention reduces the copper ion between the anode active material particles and adsorbs the copper ion, thereby allowing the copper metal to serve as a conductive agent, It is possible to improve the electronic conductivity between the active materials by causing the reduced copper metal to be adsorbed to the fine voids between the active materials that are difficult to contact with the active material.

In order to achieve the above object, the cathode of the lithium secondary battery of the present invention is characterized in that copper metal reduced between the anode active material particles coated on the anode current collector is adsorbed.

According to another aspect of the present invention, there is provided a method of manufacturing a negative electrode of a lithium secondary battery, comprising: coating a negative electrode mixture on a negative electrode collector; immersing the negative electrode collector coated with the negative electrode mixture in a solution containing copper And a step of adsorbing the copper ions between the anode active material particles in the negative electrode mixture by applying a constant voltage to the solution.

A lithium secondary battery according to still another aspect of the present invention includes the cathode electrode, the anode electrode, and the separator.

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

The present invention can provide a secondary battery which is excellent in electric conductivity and excellent in room temperature and low temperature output characteristics because a reduced amount of copper metal is adsorbed between particles of an anode active material by a cathode electrode used in a lithium secondary battery.

The negative electrode according to the present invention comprises the steps of: applying a negative electrode mixture onto an anode current collector; Immersing the negative electrode current collector coated with the negative electrode mixture in a solution containing copper; And a step of applying a constant electric potential to the solution to adsorb the copper ions on the negative electrode active material particles in the negative electrode mixture.

In the first step, a negative electrode mixture containing a negative electrode active material, a conductive material, and a binder is prepared in a slurry state and applied on the negative electrode collector.

The anode current collector generally has a thickness of 3 to 500 占 퐉 and is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. Examples of the anode current collector include copper, stainless steel, aluminum, nickel, Titanium, sintered carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel can be used. In the present invention, it is preferable to use copper.

The negative electrode current collector may have fine irregularities on its surface to increase the adhesive force of the negative electrode 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.

The negative electrode active material of the present invention can be obtained, for example, from carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, hard graphitizable carbon, carbon black, carbon nanotube, fullerene and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitride, and the like. However, the present invention is not limited to these. In the present invention, it is preferable to use graphite.

The binder is a component that assists in bonding between the negative electrode active material and the conductive material and bonding to the negative electrode collector. The binder is selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, Polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, various of these, Copolymers and the like.

The conductive material is a component for further improving the conductivity of the electrode active material. The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and 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.

After the negative electrode mixture is applied onto the negative electrode collector, the negative electrode coated with the negative electrode mixture is immersed in a solution containing copper. In addition, after immersing the negative electrode, a certain potential is applied to the solution so that the copper ions are adsorbed between the negative electrode active material particles in the negative electrode mixture.

1, a negative electrode material mixture 22 is prepared on a potentiostat 10 in the form of a slurry composition on a negative electrode collector 21, The cathode electrode 20, the platinum counter electrode 30, and the reference electrode Ag / AgCl 40 are connected to a part of the whole. Then, a constant electric potential, to which the cathode electrode, the platinum electrode, and the reference electrode are connected as described above, is immersed in the 1M aqueous solution of copper sulfate (50).

Then, a voltage of 0.1 V or less relative to the Ag / AgCl reference electrode is applied to reduce the copper ions in the aqueous copper sulfate solution, adsorb the reduced copper ions to the negative electrode, .

The oxidation / reduction potential of a common copper ion is 0.34 V (standard hydrogen electrode potential). When the Ag / AgCl is used as a reference electrode, when a voltage of 0.1 V is applied, it is confirmed that the copper ion is reduced to the cathode. In order for copper to be reduced from the solution containing copper ions according to the present invention and adsorbed between the anode active material particles, it is preferable to apply a potential of about 0.1 V or less to the Ag / AgCl reference electrode.

The solution containing copper is preferably an aqueous solution in which at least one copper-containing substance selected from the group consisting of copper sulfate, copper acetate, and copper nitrate is dissolved in water.

The cathode electrode of the present invention is formed by immersing a cathode electrode coated with a negative electrode mixture containing a negative electrode active material represented by graphite, a conductive material for improving the conductivity of the electrode, and a binder in an aqueous solution containing copper ions, The copper ions are reduced and adsorbed between the graphite active particles of the cathode electrode by applying electric potential to improve the conductivity between the graphite particles to improve the room temperature output and the low temperature output.

In the meantime, the present invention relates to a negative electrode prepared by applying a negative electrode material on a positive electrode collector and drying the negative electrode, wherein the negative electrode includes a negative electrode on which copper ions reduced between the negative electrode active material particles coated on the negative electrode collector as described above are adsorbed, The present invention also provides a lithium secondary battery including a separator.

Specific examples of the cathode 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 and Cu ₂ V ₂ O ₇ ; Formula LiNi _1-x MxO ₂ (Here, M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, 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. Preferably, the cathode 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 lithium secondary battery of the present invention has a structure in which a nonaqueous electrolyte solution containing a lithium salt is impregnated in an electrode assembly having a separator interposed between an anode and a cathode.

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 Celgard ^TM 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 improve 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 non-aqueous electrolyte and a lithium salt. 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 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, 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 charge / discharge characteristics, flame retardancy, etc., non-aqueous electrolytes may be used in the form of, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

1 is an electrochemical cell configuration diagram for adsorption of copper ions.

≪ Description of reference numerals &

10: Potentiostat 20: Cathode

21: negative electrode current collector (copper) 22: negative electrode coating portion

30: Counter Electrode (Pt)

40: Reference electrode (Ag / AgCl, KCl (saturated)

50: 1M CuSO ₄ solution

Claims (16)

Wherein a reduced amount of copper metal is adsorbed between the negative electrode active material particles applied on the negative electrode current collector, Wherein the reduction of the copper metal is performed by immersing the negative electrode current collector coated with the negative active material in a solution containing copper and applying a constant voltage thereto. delete The negative electrode of a lithium secondary battery according to claim 1, wherein the voltage is 0.1 V or less of the Ag / AgCl reference electrode. The negative electrode of a lithium secondary battery according to claim 1, wherein the solution containing copper is an aqueous solution in which at least one copper-containing material selected from the group consisting of copper sulfate, copper acetate, and copper nitrate is dissolved in water. The negative electrode of a lithium secondary battery according to claim 1, wherein the negative electrode collector is copper. The negative electrode of a lithium secondary battery according to claim 1, wherein the negative electrode active material is graphite. Applying an anode mixture onto the anode current collector; Immersing the negative electrode current collector coated with the negative electrode mixture in a solution containing copper; And And applying a constant voltage to the solution to adsorb the copper ions between the negative electrode active material particles in the negative electrode mixture. The method of manufacturing a cathode according to claim 7, wherein the anode current collector is copper. 8. The method according to claim 7, wherein the negative electrode material mixture comprises a negative electrode active material, a conductive material, and a binder. The negative active material according to claim 9, wherein the negative electrode active material is at least one carbon or graphite material selected from the group consisting of natural graphite, artificial graphite, expanded graphite, carbon fiber, hard graphitizable carbon, carbon black, carbon nanotube, fullerene, ; At least one metal selected from the group consisting of Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti capable of being alloyed with lithium; A composite of the metal and the compound containing the metal and the carbon or graphite material; And a lithium-containing nitride. The method of manufacturing a cathode of a lithium secondary battery according to claim 1, The lithium secondary battery according to claim 9, wherein the conductive material is at least one selected from the group consisting of graphite, carbon black, conductive fibers, metal powder, conductive whisker, conductive metal oxide and polyphenylene derivative. Gt; The method of claim 9, wherein the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcelluloses, regenerated cellulose, polyvinylpyrrolidone Based material selected from the group consisting of tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof Wherein the negative electrode is made of a metal. The lithium secondary battery according to claim 7, wherein the solution containing copper is an aqueous solution in which at least one copper-containing material selected from the group consisting of copper sulfate, copper acetate, and copper nitrate is dissolved in water. Gt; 8. The method as claimed in claim 7, wherein the voltage is 0.1 V or less of the Ag / AgCl reference electrode. The method for manufacturing a negative electrode of a lithium secondary battery according to claim 7, wherein the negative electrode active material is graphite. A lithium secondary battery comprising the negative electrode according to any one of claims 1 to 6.

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