KR20210157763A - Anode for lithium secondary battery and Lithium secondary battery comprising the same - Google Patents

Abstract

Disclosed are a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, wherein the negative electrode for a lithium secondary battery includes: a negative electrode current collector; a metal oxide layer positioned on the upper surface of the negative electrode current collector; a reduced graphene oxide layer positioned on the upper surface of the metal oxide layer; and a negative electrode active material layer positioned on the upper surface of the reduced graphene oxide layer, and the reduced graphene oxide layer and the metal oxide layer are chemically bonded to each other.

Description

Anode for lithium secondary battery and lithium secondary battery comprising the same

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery having the same. More particularly, it relates to an anode for a lithium secondary battery having improved lifespan characteristics and a lithium secondary battery having the same.

In recent years, the market for electric vehicles, robots, and power storage devices has rapidly developed, requiring secondary batteries with high energy density, stability, miniaturization, weight reduction, and long lifespan. Whether to be applied to such a large-scale field depends on securing the performance of the secondary battery with an energy density per weight or volume higher than the current level of energy density.

Graphite, which is currently commercialized as an anode active material for lithium-ion batteries, has a theoretical capacity of 372 mAh/g (about 160Wh/kg). Silicon (Si), which has a capacity (4200 mAh/g) more than 10 times that of graphite, is attracting attention as a negative electrode material for a next-generation nonaqueous electrolyte secondary battery. In addition, as a new material to replace carbon-based materials such as graphite, it has been proposed to use various non-carbon-based materials as negative electrode active materials in addition to silicon alloying with lithium and exhibiting high theoretical capacity.

However, in the process of alloying with lithium, cracks in the inside and surface of the electrode are generated due to a high volume expansion rate in the silicon-based material, and the active material is removed from the current collector. side effects may occur.

Accordingly, an object of the present invention is to provide an anode with improved adhesion between an electrode/metal current collector and a lithium secondary battery having the same in order to secure the lifespan characteristics of a high-capacity anode.

In order to solve the above problems, according to one aspect of the present invention, there is provided a negative electrode for a lithium secondary battery of the following embodiment.

According to the first embodiment, the negative electrode current collector; a metal oxide layer positioned on the upper surface of the negative electrode current collector, and a reduced graphene oxide layer positioned on the upper surface of the metal oxide layer; and an anode active material layer positioned on the upper surface of the reduced graphene oxide layer;

There is provided a negative electrode for a lithium secondary battery in which the reduced graphene oxide layer and the metal oxide layer are chemically bonded to each other

According to a second embodiment, according to the first embodiment,

The reduced graphene oxide layer may have a thickness of 0.5 to 100 nm.

According to a third embodiment, according to the first or second embodiment,

The metal oxide layer may have a thickness of 1 to 100 nm.

According to a fourth embodiment, according to any one of the first to third embodiments,

The oxygen content of the reduced graphene oxide may be 0.1 to 15 atomic percent.

According to a fifth embodiment, according to any one of the first to fourth embodiments,

When the reduced graphene oxide layer is coated with graphene oxide on the anode current collector, a spontaneous reduction reaction of the graphene oxide occurs due to a difference in standard reduction potential between the graphene oxide and the anode current collector, and is formed without the need for an additional reduction process can be

According to a sixth embodiment, according to any one of the first to fifth embodiments,

A chemical bond between the reduced graphene oxide and the metal oxide layer of the reduced graphene oxide layer may be formed by a redox reaction between the graphene oxide and the negative electrode current collector.

According to one aspect of the present invention, there is provided a lithium secondary battery of the following embodiments.

According to a seventh embodiment,

an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a battery container accommodating the electrode assembly; And in the lithium secondary battery having a non-aqueous electrolyte injected into the battery container,

A lithium secondary battery is provided, wherein the negative electrode is an anode for a lithium secondary battery according to any one of the first to sixth embodiments.

According to one aspect of the present invention, there is provided a method of manufacturing a negative electrode for a lithium secondary battery according to the following embodiments.

According to an eighth embodiment,

Preparing a dispersion containing graphene oxide and a dispersion medium;

The dispersion is applied to at least one surface of the negative electrode current collector and dried, and a spontaneous redox reaction occurs at the interface between the graphene oxide and the negative electrode current collector due to the reduction potential difference between the graphene oxide of the dispersion and the negative electrode current collector. forming a graphene oxide layer and a metal oxide layer; and

Forming a negative electrode active material layer by coating and drying a negative electrode slurry comprising a negative electrode active material, a binder, a conductive material, and a slurry dispersion medium on at least one surface of the negative electrode current collector on which the reduced graphene oxide layer and the metal oxide layer are formed There is provided a method for manufacturing a negative electrode for a lithium secondary battery of claim 1, comprising a.

According to one embodiment of the present invention, the adhesive force between the current collector and the anode active material layer is improved, and through this adhesion improvement, a negative active material having a large volume expansion and excellent capacity like a silicon-based active material can be applied, and as a result, a high capacity It is possible to provide a secondary battery with improved lifespan characteristics by providing the negative electrode and the negative electrode.

By forming a reduced graphene oxide (rGO) layer on the anode current collector, a redox reaction occurs between the reduced graphene oxide and the metal current collector to form a chemical bond, so the adhesion between the two layers is improved. can be very strong.

In order to improve the adhesion between the current collector and the anode active material layer, a coating layer containing reduced graphene oxide having a thickness of several nanometers is applied, thereby conventionally applying a primer layer having a thickness of several micrometers to the current collector. In contrast, the energy density can be greatly improved.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the above-described content of the present invention, so the present invention is limited to the matters described in those drawings It should not be construed as being limited.
1 is a schematic diagram of a cross-section of a cathode according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

1, the negative electrode 100 for a lithium secondary battery according to an aspect of the present invention,

anode current collector 110; a metal oxide layer 120 positioned on the upper surface of the negative electrode current collector 110 , and a reduced graphene oxide layer 130 positioned on the upper surface of the metal oxide layer 120 ; and a negative active material layer 140 positioned on the upper surface of the reduced graphene oxide layer 130;

The reduced graphene oxide layer 130 and the metal oxide layer 120 are chemically bonded to each other.

The current collector may include stainless steel, aluminum, nickel, titanium, calcined carbon, copper; stainless steel surface-treated with carbon, nickel, titanium or silver; aluminum-cadmium alloy; Non-conductive polymer surface-treated with a conductive material; Non-conductive polymer surface-treated with metal; and a material selected from among conductive polymers.

In addition, the current collector may have a thickness of 3 μm to 500 μm, but is not limited thereto, and the size of the porous current collector is also not particularly limited, and may be appropriately selected according to the use of the electrode.

As used herein, the term “graphene oxide” refers to an oxide formed by oxidizing graphite, and since such graphene oxide can prepare a dispersion solution unlike graphite, it has a feature that thin film is possible. Therefore, when graphene oxide is thinned using a dispersion solution of graphene oxide and then reduced, it becomes possible to form graphene in a sheet shape. In addition, the graphene oxide may include a structure in which a functional group containing oxygen, such as a carboxyl group, a hydroxyl group, or an epoxy group, is bonded to a single layer graphene.

As used herein, "graphene" refers to a polycyclic aromatic molecule formed by covalently connecting a plurality of carbon atoms to each other, and the carbon atoms connected by covalent bonds form a 6-membered ring as a basic repeating unit, but a 5-membered ring and / Or it is also possible to further include a 7-membered ring. Thus, the graphene appears as a single layer of carbon atoms covalently bonded to each other (usually sp2 bonds). The graphene may have various structures, and such a structure may vary depending on the content of a 5-membered ring and/or a 7-membered ring that may be included in the graphene. The graphene may consist of a single layer, but it is also possible to form a plurality of layers by stacking a plurality of them, and a thickness of up to 100 nm may be formed. have.

In the present invention, "reduced graphene oxide" means a reduced product obtained by reducing the graphene oxide. rGO".

The reduced graphene oxide as described above does not have the form of complete graphene (C=C/C-C conjugated structure), and contains less C=C than graphene. That is, as elements other than carbon, oxygen atoms or nitrogen atoms are partially mixed, so that various band gaps exist between the reduced graphene oxides.

According to an embodiment of the present invention, the reduced graphene oxide is 0.1 to 15 atomic percent (at.%), or 0.1 to 10 atomic percent (at.%), or 0.1 to 5 atomic percent (at. %) of oxygen. When the oxygen content of the reduced graphene oxide satisfies this range, it is advantageous in terms of reducing the electrical resistance between the active material layer and the current collector by improving the electrical conductivity of the reduced graphene.

According to one embodiment of the present invention, the thickness of the reduced graphene oxide layer may be 0.5 to 100 nm, or 2 to 10 nm. When the thickness of the reduced graphene oxide layer satisfies this range, it is advantageous in terms of minimizing an increase in electrical resistance while improving adhesion between the active material layer and the current collector.

In addition, the thickness of the metal oxide layer may be 1 to 100 nm, or 2 to 50 nm. When the thickness of the metal oxide layer satisfies this range, it is advantageous in terms of simultaneously securing electrical properties and adhesion between the active material and the current collector.

A method of manufacturing a negative electrode for a lithium secondary battery according to an aspect of the present invention,

Preparing a dispersion containing graphene oxide and a dispersion medium;

The dispersion is applied to at least one surface of the negative electrode current collector and dried, and a spontaneous redox reaction occurs at the interface between the graphene oxide and the negative electrode current collector due to the reduction potential difference between the graphene oxide of the dispersion and the negative electrode current collector. forming a graphene oxide layer and a metal oxide layer; and

Forming a negative electrode active material layer by coating and drying a negative electrode slurry comprising a negative electrode active material, a binder, a conductive material, and a slurry dispersion medium on at least one surface of the negative electrode current collector on which the reduced graphene oxide layer and the metal oxide layer are formed includes ;

First, a dispersion containing graphene oxide and a dispersion medium is prepared.

As the dispersion medium, any solvent that does not chemically affect graphene oxide can be applied without limitation, for example, water, ethanol, methanol, acetone, isopropyl alcohol, butanol, and the like may be used.

In the dispersion, the graphene oxide may be included in an amount of 0.0001 to 0.02 parts by weight, or 0.001 to 0.008 parts by weight based on 100 parts by weight of the dispersion medium.

Next, the dispersion is applied to at least one surface of the negative electrode current collector and dried.

At this time, the coating and drying method is not particularly limited as long as it is a method commonly used in the art.

According to one embodiment of the present invention, the coating method using a slot die may be used as the coating method, and in addition, the Mayer bar coating method, gravure coating method, dip coating method, spray coating method, etc. may be used.

In addition, the drying process may be carried out by methods such as heat treatment at a temperature capable of maximally removing moisture contained in graphene oxide along with evaporation of the dispersion medium in the dispersion, hot air injection, and the like. Specifically, the drying process may be carried out at a temperature equal to or higher than the boiling point of the solvent or lower than the melting point of the binder, and more specifically, may be carried out at 25 to 150 °C, or at a temperature of 40 to 100 °C for 1 to 50 hours. can be

At this time, a spontaneous redox reaction occurs at the interface between the graphene oxide and the negative electrode current collector due to the reduction potential difference between the graphene oxide of the dispersion and the negative electrode current collector to form a reduced graphene oxide layer and a metal oxide layer.

By the redox reaction between the graphene oxide and the negative electrode current collector, a chemical bond between the reduced graphene oxide and the metal oxide layer of the reduced graphene oxide layer is formed.

When the graphene oxide and a metal having a lower reduction potential than that of the graphene oxide come into contact in an aqueous environment, a spontaneous redox reaction may proceed due to the reduction potential difference. The oxygen functional group removed from the graphene oxide during the spontaneous redox reaction may combine with the metal, resulting in the formation of a metal oxide. As a result, a layer structure of reduced graphene oxide-metal oxide-metal may be sequentially formed.

Next, on at least one surface of the negative electrode current collector on which the reduced graphene oxide layer and the metal oxide layer are formed, a negative electrode slurry comprising a negative electrode active material, a binder, a conductive material, and a slurry dispersion medium is applied and dried to form a negative electrode active material layer to form

As an anode active material, a carbon material, lithium metal, silicon-based, or tin-based material, which can typically be occluded and released with lithium ions, can be used, and metal oxides such as _{TiO 2} and SnO _{2 with a potential of less than 2V to lithium are also possible.} do. Preferably, a carbon material may be used, and as the carbon material, both low-crystalline carbon and high-crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch High-temperature firing of mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, petroleum derived cokes, and tar pitch derived cokes Carbon is an example.

In one embodiment of the present invention, the adhesive force between the current collector and the negative electrode active material layer is improved, and through this improvement in adhesive strength, a negative active material having a large volume expansion and excellent capacity like a silicon-based active material can be applied, and as a result, a high capacity negative electrode and , it is possible to provide a secondary battery with improved lifespan characteristics by providing such a negative electrode.

The silicon-based negative active material includes Si and is not particularly limited as long as it is a material capable of alloying with lithium. Specifically, the Si-based negative active material may include Si, SiO _x (0<x<2), SiC, or two or more of these.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 50% by weight based on the total weight of the electrode mixture. Examples of such binders include polyvinyl alcohol, polyacrylic acid, polyacrylonitrile, polyvinylidene fluoride, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrroly. Don, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ter polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), polyacrylic acid, alkali cation or polyacrylic acid substituted with ammonium ion, alkali Poly(alkylene-maleic anhydride) copolymer substituted with cation or ammonium ion, poly(alkylene-maleic acid) copolymer substituted with alkali cation or ammonium ion, polyethylene oxide, fluororubber, or two or more of these can More specifically, the polyacrylic acid substituted with the alkali cation includes lithium-polyacrylate (Li-PAA, polyacrylic acid substituted with lithium), and the poly(alkylene-maleic anhydride) copolymer substituted with the alkali cation. The sieve may include lithium-substituted polyisobutylene-maleic anhydride. According to one embodiment of the present invention, a mixture of PVA (polyvinyl alcohol) and PAA (polyacrylic acid) is used as the binder, or a mixture of PVA (polyvinyl alcohol) and PAA (polyacrylic acid) and CMC (carboxy methyl cellulose) may be used.

The conductive material is a component that does not cause chemical change in the battery, and includes, for example, graphite such as natural graphite or artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black (brand name), carbon nanotube, carbon nanofiber, channel black, furnace black, lamp black, thermal black, conductive fibers, such as carbon fiber and metal fiber, fluorocarbon, metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium oxide; Conductive materials, such as polyphenylene derivatives, etc. can be used.

According to one embodiment of the present invention, when the negative electrode is manufactured by applying a mixture of the negative electrode active material including the negative electrode active material, the conductive material and the binder on the negative electrode current collector, the negative electrode active material, the conductive material and the binder are formed by a dry method. It may be prepared by directly applying the solid mixture, or may be prepared by adding the negative electrode active material, the conductive material and the binder to the dispersion medium by a wet method, then applying the mixture in the form of a slurry by stirring, and then removing the dispersion medium by drying or the like. At this time, as the dispersion medium used in the case of the wet method, an aqueous medium of water (deionized water, etc.) may be used, or an organic type such as N-methyl-pyrrolidone (NMP, N-methyl-2-pyrrolidone) or acetone. A medium may also be used.

A secondary battery according to an embodiment of the present invention includes the above-described negative electrode and positive electrode, and a separator interposed between the positive electrode and the negative electrode.

The positive electrode may be prepared by applying a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector and drying the mixture, and, if necessary, may further include a filler in the mixture. The cathode active material may _{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 Formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO _{2 ;} lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O _{7 ;} 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 (where 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 an alkaline earth metal ion; disulfide compounds; And the like Fe ₂ (MoO _{4) 3,} but is not limited to these.

For the positive electrode, the conductive material, the current collector, and the binder may refer to the above-described 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 0.01 to 10 μm, and the thickness is generally 5 to 300 μm. As such a separation membrane, For example, olefin polymers, such as chemical-resistant and hydrophobic polypropylene; A film, sheet, or non-woven fabric made of glass fiber or polyethylene is used. Meanwhile, the separation membrane may further include a porous layer including a mixture of inorganic particles and a binder resin on the outermost surface.

In one embodiment of the present invention, the electrolyte contains an organic solvent and a predetermined amount of a lithium salt, and as a component of the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propionate (MP), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran , N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), vinylene carbonate (VC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, formic acid propyl, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, butyl propionate, or mixtures thereof. Also, halogen derivatives of the above organic solvents can be used, and linear ester materials are also available. can be used The lithium salt is a material easily 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 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

Finally, a lithium secondary battery may be provided by configuring an electrode assembly by interposing a separator between the negative electrode and the positive electrode, accommodating it in a battery case, and injecting an electrolyte.

The electrolyte may include a lithium salt and an organic solvent for dissolving the lithium salt.

The lithium salt may be used without limitation as long as it is commonly used in electrolytes for secondary batteries. For example, as an anion of the lithium salt ^{, F -} , Cl ^- , 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 ^- One selected from the group consisting of may be used.

The organic solvent included in the electrolyte may be used without limitation as long as it is conventionally used, and representatively, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide At least one selected from the group consisting of side, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are highly viscous organic solvents and have a high dielectric constant, so they can be used preferably because they dissociate lithium salts in the electrolyte well, and dimethyl carbonate and diethyl in these cyclic carbonates When a low-viscosity, low-dielectric constant linear carbonate such as carbonate is mixed in an appropriate ratio, an electrolyte having a high electrical conductivity can be prepared, which can be more preferably used.

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

The battery according to an embodiment of the present invention may be of a stack type, a winding type, a stack and folding type, or a cable type, and may be used in a battery cell used as a power source of a small device, as well as a plurality of battery cells It can be preferably used as a unit cell in a medium or large-sized battery module. Preferred examples of the mid-to-large device include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. In particular, it is useful for hybrid electric vehicles and new and renewable energy storage batteries, which are areas requiring high output. can be used

Hereinafter, test examples and examples will be described in detail to help the understanding of the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example 1

<Formation of coating layer on current collector>

A dispersion was prepared by mixing 0.002 parts by weight of graphene oxide with 100 parts by weight of a dispersion medium prepared by mixing ethanol and water in a weight ratio of 50:50.

The prepared dispersion was applied on one side of a copper foil having a thickness of 15 μm, which is an anode current collector, in a bar coating method, and dried at a temperature of 60° C. for 20 minutes.

When the dispersion is coated on the copper foil, a spontaneous reduction reaction proceeds at the interface due to the reduction potential difference between graphene oxide and the metal, and a metal oxide layer with a thickness of 10 nm on the metal current collector and on the metal oxide layer A reduced graphene oxide (rGO) layer with a thickness of 3.5 nm was formed on the

<Production of cathode>

Si-based active material, Si as a binder, PVA (polyvinyl alcohol)-PAA (polyacrylic acid) copolymer (PVA-PAA copolymer, PVA:PAA=60:40 (weight ratio)), CMC (carboxymethyl cellulose), conductive material A slurry for the active material layer was prepared by mixing a mixture of raw carbon black in a weight ratio of 70:10:20, and water as a dispersion medium, and mixing the mixture and dispersion medium in a weight ratio of 1:2.

Using a slot die, the slurry for the active material layer is coated on the upper surface of the coating layer on the copper (Cu) thin film, which is the negative current collector on which the coating layer is formed. was formed.

The active material layer thus formed was rolled by a roll pressing method to prepare an anode having a single-layered active material layer having a thickness of 45 μm. Based on the dry weight of the anode active material layer, the loading amount was 16 mg/cm ² .

<Production of anode>

_{Li(Ni 0.8} Mn _0.1 Co _0.1 )O ₂ (NCM-811) as a cathode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 96:2:2 as a solvent It was added to phosphorus N-methylpyrrolidone (NMP) to prepare a cathode active material slurry. The slurry was coated on one surface of an aluminum current collector having a thickness of 15 μm, and drying and rolling were performed under the same conditions as the negative electrode to prepare a positive electrode. At this time, the loading amount based on the dry weight of the positive electrode active material layer was 20 mg/cm ² .

<Manufacture of lithium secondary battery>

Fluorenyl right ethylene carbonate (FEC), and ethyl methyl carbonate (EMC) 3: it was dissolved to a concentration of the LiPF ₆ in a mixed organic solvent in the proportion of 7 (volume ratio) to prepare a 1.0M aqueous electrolytic solution.

After interposing the polyolefin separator between the positive electrode and the negative electrode prepared above, the electrolyte was injected to prepare a lithium secondary battery.

<Production of half coin cell>

Fluorenyl right ethylene carbonate (FEC), and ethyl methyl carbonate (EMC) 3: it was dissolved to a concentration of the LiPF ₆ in a mixed organic solvent in the proportion of 7 (volume ratio) to prepare a 1.0M aqueous electrolytic solution.

After interposing the polyolefin separator between the negative electrode prepared above and the lithium metal counter electrode, the electrolyte was injected and used to prepare a half cell.

Comparative Example 1:

A cathode and a cathode in the same manner as in Example 1, except that the step of forming a metal oxide layer on a metal current collector and a reduced graphene oxide (rGO) layer on the metal oxide layer was omitted. A lithium secondary battery and a half cell were manufactured.

Experimental Example 1: Evaluation of adhesion between the current collector and the anode active material layer

After preparing the negative electrode prepared in Example 1 and Comparative Example 1 to a size of 2.5 cm x 15 cm, immersed in a dimethyl chloride (DMC) solvent and dried to prepare a sample for the adhesion test. Adhere the double-sided tape prepared in the size of 2 x 12 cm to the slide glass, and attach the other side of the double-sided tape to the sample. The force to peel the electrode from the current collector by pulling, that is, the adhesive force, was measured, and the measurement angle between the slide glass and the electrode was 90°.

In this case, the peel strength of the negative electrode was measured by measuring the initial adhesive strength immediately after the negative electrode was prepared and the adhesive strength after one week after the negative electrode was prepared and stored in a chamber at 60 ° C. The results are shown in Table 1 below.

Adhesion (gf/cm) Example 1 Comparative Example 1 Early 23 21 after 1 week 19.2 11.5

Referring to Table 1, it can be seen that the negative electrode of Example 1 is superior to the comparative example in the adhesive force and the adhesive force retention of the Example 1 not only in the initial adhesive force but also in the change in the adhesive force after 1 week.

Experimental Example 2: Evaluation of the life (cycle) characteristics of the secondary battery

For the coin half cells prepared in Example 1 and Comparative Example 1, both charging and discharging were at a rate of 0.5 C and a voltage condition of 0.005 V - 1.5 V vs. Life characteristics were evaluated by performing 20 cycles with Li/Li+, and the results are shown in Table 2 below.

Initial discharge capacity (mAh/g) Discharge capacity after 20 cycles (mAh/g) Example 1 3,408 3,238 Comparative Example 1 3,420 3,197

Referring to Table 2, the battery of Example 1 (coin half cell) to which a negative electrode having a reduced graphene oxide layer was applied was charged compared to the battery of Comparative Example 1 to which a negative electrode without a reduced graphene oxide layer was applied. It was found that the discharge cycle characteristics were excellent.

Claims (8)

negative electrode current collector; a metal oxide layer positioned on the upper surface of the negative electrode current collector, and a reduced graphene oxide layer positioned on the upper surface of the metal oxide layer; and an anode active material layer positioned on the upper surface of the reduced graphene oxide layer;
A negative electrode for a lithium secondary battery in which the reduced graphene oxide layer and the metal oxide layer are chemically bonded to each other. According to claim 1,
A negative electrode for a lithium secondary battery, characterized in that the reduced graphene oxide layer has a thickness of 0.5 to 100 nm. According to claim 1,
A negative electrode for a lithium secondary battery, characterized in that the thickness of the metal oxide layer is 1 to 100 nm. According to claim 1,
The negative electrode for a lithium secondary battery, characterized in that the oxygen content of the reduced graphene oxide is 0.1 to 15 atomic percent. According to claim 1,
When the reduced graphene oxide layer is coated with graphene oxide on the anode current collector, a spontaneous reduction reaction of the graphene oxide occurs due to a difference in standard reduction potential between the graphene oxide and the anode current collector, and is formed without the need for an additional reduction process A negative electrode for a lithium secondary battery, characterized in that it becomes. According to claim 1,
A negative electrode for a lithium secondary battery in which a chemical bond between the reduced graphene oxide and the metal oxide layer of the reduced graphene oxide layer is formed by a redox reaction between the graphene oxide and the negative electrode current collector. an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a battery container accommodating the electrode assembly; And in the lithium secondary battery having a non-aqueous electrolyte injected into the battery container,
The lithium secondary battery wherein the negative electrode is the negative electrode for a lithium secondary battery according to any one of claims 1 to 6. Preparing a dispersion containing graphene oxide and a dispersion medium;
The dispersion is applied to at least one surface of the negative electrode current collector and dried, and a spontaneous redox reaction occurs at the interface between the graphene oxide and the negative electrode current collector due to the reduction potential difference between the graphene oxide of the dispersion and the negative electrode current collector. forming a graphene oxide layer and a metal oxide layer; and
Forming a negative electrode active material layer by coating and drying a negative electrode slurry comprising a negative electrode active material, a binder, a conductive material, and a slurry dispersion medium on at least one surface of the negative electrode current collector on which the reduced graphene oxide layer and the metal oxide layer are formed A method of manufacturing a negative electrode for a lithium secondary battery of claim 1, comprising a.

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