KR20110029321A - Electrode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: An electrode for a lithium secondary battery is provided to prevent partial degeneration of an electrode since a plurality of graphen layers are inserted in an electrode, and to improve the output of a battery by reducing interface resistance. CONSTITUTION: An electrode for a lithium secondary battery includes a current collector(10) and an electrode lminate layer(20) applied on at least one side of the current collector, wherein the electrode lminate layer formed by alternately laminating a plurality of graphen layers(22) and electrode active material layer(21). One of the graphen layers laminated on the current collector is contacted with the current collector.

Description

Electrode for lithium secondary battery and lithium secondary battery having same {Electrode for lithium secondary battery and Lithium secondary battery comprising the same}

The present invention relates to a lithium secondary battery electrode and a lithium secondary battery having the same.

Recently, lithium secondary batteries have received the most attention as batteries with high energy density and long lifespan. Typically, a lithium secondary battery includes an anode made of a carbon material or a lithium metal alloy, a cathode made of a lithium metal oxide, and an electrolyte in which lithium salt is dissolved in an organic solvent.

Typically, the electrode of a lithium secondary battery is prepared by applying an electrode mixture slurry prepared by including an electrode active material, a binder, a conductive material and the like on a current collector and compression drying.

Specifically, the negative electrode mixture includes a negative electrode active material, a binder for fixing the negative electrode active material, and a conductive material for improving electrical conductivity. In the case of the negative electrode, a carbon material is mainly used as an electrode active material. In the case of a carbon-based active material, the carbon-based active material has a high conductivity, and thus also plays a role as a conductive material. As the charging and discharging are repeated, the moving path of the electrons may become unstable. Therefore, it is preferable to use a conductive material to compensate for this.

In addition, the positive electrode mixture is prepared similarly to the negative electrode mixture. Lithium metal oxide is mainly used as the positive electrode active material. Since most of the ceramic materials have low electrical conductivity, the use of a conductive material is essential.

As the conductive material used for the electrode mixture, conductive carbon is usually used. For example, various conductive carbon materials such as carbon black and graphite powder are used. Various conductive carbon materials can be largely divided into amorphous or crystalline carbon. Amorphous carbon has a relatively large specific surface area, which has the advantage of reducing the amount of conductive material used, but has the disadvantage of poor conductivity. In contrast, crystalline graphite has a relatively high conductivity, but has a disadvantage in that the amount of use is high.

In addition, since the conventional conductive material is simply mixed with the active material to form an electrode mixture, a difference may occur in uniformity of ion conductivity in the electrode depending on the degree of mixing, and may cause partial degeneration of the electrode.

Accordingly, the problem to be solved by the present invention is to provide a new conductive material that can ensure uniformity of ion conductivity in the active material.

In addition, another object of the present invention is to provide a new electrode that reduces the interface resistance between the mixture layer and the current collector, increases the contact area to improve the capacity.

In order to solve the above problems, according to the present invention, a lithium secondary battery electrode having a current collector and an electrode mixture layer applied to at least one surface of the current collector, the electrode mixture layer has a plurality of graphene (graphene) The layer and the electrode active material layer are characterized in that the alternately formed.

The thickness of one graphene layer of the electrode mixture layer according to the present invention is preferably several nm. Optionally, the lowermost graphene layer of the plurality of graphene layers stacked on the current collector is in contact with the current collector. The graphene layer may be formed by vapor deposition.

The electrode mixture layer according to the present invention may be coated on a current collector to form both a positive electrode, a negative electrode, or a positive electrode and a negative electrode. The positive electrode and the negative electrode thus prepared may be used to manufacture a lithium secondary battery through a separator therebetween. have.

In the electrode of the present invention, a plurality of graphene layers are inserted in the electrode mixture layer to ensure uniformity of ion conductivity in the electrode, thereby preventing partial degradation of the electrode.

In addition, when the graphene layer is in contact with the current collector, the output of the battery can be improved by reducing the interface resistance between the mixture layer and the current collector, and the battery capacity is also improved by increasing the contact area between the current collector and the mixture layer. .

Hereinafter, the present invention will be described in detail with reference to the drawings. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

In figure 1 an embodiment of an electrode 1 according to the invention is shown schematically. However, the configuration described in the embodiments and drawings described below are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, which can be replaced at the time of the present application It should be understood that there may be various equivalents and variations.

Referring to FIG. 1, the structure of the electrode 1 of the present invention having the electrode mixture layer 20 formed by alternately stacking the active material layer 21 and the graphene layer 22 on the current collector 10 can be seen. have.

Graphene has a sheet-like structure in which carbon atoms are arranged in a hexagonal mesh shape, and has high electrical conductivity. In addition, carbon nanotubes, which are known as highly conductive materials, have electrical conductivity only in one direction because they have a one-dimensional structure, but graphene has a two-dimensional structure in a planar shape, and thus, two-dimensional in a plane. It is characterized by having electrical conductivity and thermal conductivity in the direction.

The present invention has a structure in which a plurality of graphene layer 22 and the active material layer 21 is alternately stacked in the electrode mixture layer 20 to maximize the excellent electrical characteristics and two-dimensional transfer characteristics of the graphene. to provide. The graphene layer 22 inserted between the active material layers 21 is formed over the mixture layer 20 to ensure uniform ion conductivity inside the mixture layer. Therefore, it is possible to maximize the excellent electrical conductivity effect of the graphene, and further, the graphene layer 22 formed on the entire mixture layer may prevent partial degradation of the electrode.

Optionally, in another embodiment of the electrode 1 of the present invention as schematically shown in FIG. 2, the graphene layer 22 is in contact with the current collector 10 and the graphene layer 22 and the active material layer 21. ) May be alternately stacked to form the mixture layer 20.

When the graphene layer 22 is in contact with the current collector 10, the interface resistance between the mixture layer 20 and the current collector 10 may be reduced. In particular, when used for the negative electrode, since a carbon-based material is mainly used as the active material, graphene formed of the same element is more preferable for lowering the interfacial resistance. When the interface resistance between the current collector 10 and the mixture layer 20 is lowered, there is an effect that the output of the battery is improved. In addition, the graphene layer 22 coming into contact with the current collector 10 may increase the adhesive force and contact area between the mixture layer 20 and the current collector 10, thereby contributing to the improvement of battery capacity.

The graphene layer 22 according to the present invention may be formed by various methods, but is preferably formed by vapor deposition in order to have a uniform surface shape. The vapor deposition method includes physical vapor deposition (PVD) or chemical vapor deposition (CVD), and any one of the present invention may be applied without limitation.

In addition, the thickness of one graphene layer 22 formed in accordance with the present invention is preferably several nm. More preferred graphene layer 22 is a monolayer two-dimensional planar structure in the form of a carbon layer of several nm thickness, the thickness can be seen as the diameter of the carbon atom. It is expected that the function as a conductive material will be somewhat limited if it forms agglomerated or bulk carbon rather than a single layer.

In the electrode mixture layer 20 according to the present invention, the electrode active material layer 21 may be used without any particular limitation to an active material layer applied to a conventional electrode. The electrode active material layer 21 may include an electrode active material, a binder, and a conductive material, and various additives may be used as necessary.

If the electrode used is a negative electrode, as the negative electrode active material, a carbon material, lithium metal, silicon or tin, etc., in which lithium ions may be occluded and released, may be used. Preferably, the carbon material is mainly used. As the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber. High temperature calcined carbon such as (mesophase pitch based carbon fiber), meso-carbon microbeads, Mesophase pitches and petroleum or coal tar pitch derived cokes.

In addition, if the electrode used is a positive electrode, a lithium-containing transition metal oxide may be preferably used as the positive electrode active material, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-y Co _y O ₂ , LiCo _1-y Mn _y O ₂ , LiNi _1-y Mn _y O ₂ (O≤y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn _2-z Ni _z O ₄ , LiMn _2-z Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ , any one selected from the group consisting of or a mixture of two or more thereof Can be used. In addition to these oxides, sulfides, selenides, and halides may also be used.

Examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and the like. It can be used individually or in mixture of 2 or more types.

As the conductive material included in the active material layer, various conductive carbons such as carbon black, acetylene black, caten black, super-P, and carbon nanotubes may be used alone or in combination of two or more thereof.

The current collector 10 in which the electrode active material layer 21 and the graphene layer 22 are stacked may be an electrode current collector used in the art without limitation. Specifically, the current collector is a highly conductive metal, and any slurry can be used as long as the slurry of the electrode active material can be easily adhered and is not reactive in the voltage range of the battery. Non-limiting examples of the positive electrode current collector may include a foil made by aluminum, nickel, or a combination thereof. Non-limiting examples of the negative electrode current collector may include a foil made by copper, gold, nickel or a copper alloy or a combination thereof.

Hereinafter, an embodiment of the manufacturing method of the electrode of the present invention will be described in detail.

The active material slurry containing the electrode active material, the binder, and the conductive material is coated on the current collector 10 to a predetermined thickness to form the active material layer 21. Graphene is vapor-deposited on the formed active material layer 21 to form a graphene layer 22. Then, the electrode 1 of the present invention may be obtained by alternately stacking the active material slurry and the graphene in the same manner.

Optionally, the graphene layer 22 is formed in a manner in which the graphene layer 22 is first formed on the current collector 10, and then the active material layer 21 is formed thereon, with a different stacking order as shown in FIG. 2. And the active material layer 21 can be laminated alternately to obtain the electrode 1 of the present invention.

In the present invention, the number of laminations of the active material layer 21 and the graphene layer 22 is not particularly limited. The number of laminations can be determined according to the specific application and required electrode thickness.

When the electrode is manufactured according to the present invention, a lithium secondary battery having a separator and an electrolyte interposed between the positive electrode and the negative electrode, which is commonly used in the art, may be manufactured using the electrode.

In the electrolytic solution used in the present invention, the lithium salt that may be included as an electrolyte may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as the lithium salt, the anion is F ^-, Cl ^-, Br ^{- _{, I -, NO 3 -,}} N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 _{^{PF 2 -, (CF 3)}} 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N _{^{-, CF 3 CF 2 (CF}} 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO _{^{3 -, CF 3 CO 2 -}} , CH 3 CO 2 -, SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^-It may be any one selected from the group consisting of.

In the electrolyte solution used in the present invention, as the organic solvent included in the electrolyte solution, those conventionally used in the electrolyte for lithium secondary batteries may be used without limitation, and typically, propylene carbonate (PC), ethylene carbonate (ethylene carbonate, EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxy Ethylene, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, any one selected from the group consisting of, or a mixture of two or more thereof may be representatively used. In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents, and thus may be preferably used because they dissociate lithium salts in electrolytes well. When a low viscosity, low dielectric constant linear carbonate, such as carbonate, is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and thus it can be more preferably used.

Optionally, the electrolyte solution stored according to the present invention may further include additives such as an overcharge inhibitor included in a conventional electrolyte solution.

In addition, as the separator, conventional porous polymer films conventionally used as separators, for example, polyolefins such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. The porous polymer film made of the polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. It is not.

The battery case used in the present invention may be adopted that is commonly used in the art, there is no limitation on the appearance according to the use of the battery, for example, cylindrical, square, pouch type or coin using a can (coin) type and the like.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 is a schematic cross-sectional view of an electrode manufactured according to an embodiment of the present invention.

2 is a schematic cross-sectional view of an electrode manufactured according to another embodiment of the present invention.

Claims (9)

In the lithium secondary battery electrode having a current collector and an electrode mixture layer applied to at least one surface of the current collector, The electrode mixture layer is a lithium secondary battery electrode, characterized in that formed by alternately stacking a plurality of graphene layer and electrode active material layer. The method of claim 1, One of a plurality of graphene layers stacked on the current collector is in contact with the current collector, the lithium secondary battery electrode. The method of claim 1, The graphene layer is a lithium secondary battery electrode, characterized in that formed by the vapor deposition method. The method of claim 1, The electrode active material layer comprises an electrode active material, a binder and a conductive material. The method of claim 4, wherein The electrode active material of the electrode active material layer, when the electrode is a negative electrode made of soft carbon, hardened carbon, natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber, carbon microspheres, liquid crystal pitch and petroleum and coal-based coke Lithium secondary battery electrode comprising any one or a mixture of two or more thereof selected from the group. The method of claim 4, wherein In the electrode active material of the electrode active material layer, when the electrode is a positive electrode, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 < b <1, 0 <c <1, a + b + c = 1), LiNi _1-y Co _y O ₂ , LiCo _1-y Mn _y O ₂ , LiNi _1-y Mn _y O ₂ (O≤y < 1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn _2-z Ni _z O ₄ LiMn _2-z Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ any one selected from the group consisting of or a mixture of two or more thereof. The method of claim 4, wherein The binder of the electrode active material layer is any one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, poly acrylonitrile and poly methyl methacrylate or two or more thereof Lithium secondary battery electrode comprising a mixture. The method of claim 4, wherein The conductive material of the electrode active material layer is any one selected from the group consisting of carbon black, acetylene black, Caten black, super-P and carbon nanotubes or a mixture of two or more thereof. In a lithium secondary battery comprising a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode, The lithium secondary battery, characterized in that the positive electrode or negative electrode is an electrode according to any one of claims 1 to 8.

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