KR102359813B1 - Anode Coated with Primer Layer Comprising CNT and Method of Manufacturing the Same - Google Patents

Abstract

The present invention, a negative electrode current collector;
A primer layer formed on at least one surface of the negative electrode current collector and including a carbon nano tube (CNT), and a first binder binding the carbon nano tube, the current collector, and the components of the negative electrode mixture layer below ; and
a negative electrode mixture layer positioned on the primer layer and including a negative active material and a second binder for binding between the negative active material particles;
It relates to a negative electrode for a secondary battery comprising a, and a method for manufacturing the same.

Description

Anode Coated with Primer Layer Comprising CNT and Method of Manufacturing the Same

The present invention relates to an anode coated with a primer layer comprising CNTs and a method for manufacturing the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used.

In addition, as interest in environmental issues has increased in recent years, electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, have been developed. There is a lot of research going on. As a power source for such electric vehicles (EVs) and hybrid electric vehicles (HEVs), lithium secondary batteries with high energy density, high discharge voltage, and output stability are mainly researched and used.

This secondary battery has a structure in which an electrode assembly capable of charging and discharging of a positive electrode/separator/negative electrode structure is mounted on a battery case, and the electrodes of the positive electrode and the negative electrode are electrode active materials and organic/inorganic compounds on one or both sides of a metal current collector. It is prepared by applying an electrode coating layer containing the electrode, drying and rolling.

However, in the electrode, the electrode coating layer repeats constant contraction and expansion during charging and discharging of the secondary battery, and this causes a phenomenon in which a portion of the electrode coating layer is detached from the current collector. And, the portion of the electrode coating layer detached from the current collector as described above causes a problem in the safety of the secondary battery or increases the internal resistance to deteriorate the overall performance of the secondary battery. In particular, in the case of an anode using artificial graphite as an active material, this phenomenon is more serious due to shape problems and deepening of volume expansion.

Accordingly, research on a method for improving the adhesion of the electrode coating layer has been actively conducted in the art, and a method including a large amount of a binder in the electrode is widely used for this purpose.

The electrode active material, conductive material, and current collector constituting the electrode are solid at room temperature and have different surface properties, so it is difficult to bond easily at room temperature. , it is possible to suppress the detachment of the electrode during the electrode coating, drying, and rolling processes.

However, if the content of the binder is increased in order to improve the adhesion of the electrode coating layer, the content of the conductive material and the active material is relatively decreased, so that the internal resistance of the electrode is increased, the electronic conductivity is lowered, and there is a problem that the capacity is reduced. have.

As a solution to this problem, an excessive amount of the conductive material may be used as a whole together with the binder. However, the excessive use of the conductive material relatively further lowers the content of the electrode active material, thereby adversely affecting the capacity of the electrode.

On the other hand, for this purpose, a configuration of forming a primer coating layer using a conductive material is adopted, but a conductive material such as carbon black has difficulties in the coating process due to its porous structure, and to adhere it to the current collector. For this purpose, there is a problem in that the consumption of the binder increases and the primer coating layer becomes thick.

Accordingly, there is a high need for an electrode technology that solves the above problems and has excellent electronic conductivity.

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

After repeated in-depth research and various experiments, the inventors of the present application have, as will be described later, a method for binding carbon nanotubes (CNTs) and components between the anode current collector and the anode mixture layer. 1 In the case of including a primer layer containing a binder, excellent adhesion and electronic conductivity between the current collector and the electrode coating layer can be secured even with a thin thickness, and it is confirmed that it is possible to prevent detachment of the mixture layer in the subsequent charging and discharging process, , came to complete the present invention.

The negative electrode for a secondary battery according to the present invention,

negative electrode current collector;

A primer layer formed on at least one surface of the negative electrode current collector and comprising a carbon nano tube (CNT), and a first binder binding the carbon nano tube, the current collector, and the components of the negative electrode mixture layer to each other. ; and

an anode mixture layer positioned on the primer layer and including a second binder for binding between the anode active material and the anode active material particles;

It is characterized in that it includes.

That is, the negative electrode according to the present invention includes a primer layer using carbon nanotubes rather than a conductive material generally used between the current collector and the negative electrode mixture layer, and has a web shape compared to a conductive material such as carbon black. It is easy to improve the electronic conductivity due to the advantage of forming a network structure of As a result, there is an effect of improving the overall performance of the secondary battery by ensuring excellent adhesion and conductivity even after charging and discharging of the secondary battery.

Moreover, compared to the case of using graphene rather than carbon nanotubes for the primer layer, the carbon nanotubes are advantageous in the formation of a web-type network structure in the thickness direction of a bar electrode having a tube shape in a three-dimensional structure, whereas , graphene has a flat planar structure as if it is formed as a single layer in the electrode thickness direction, and has good conductivity in the electrode surface direction, but lower conductivity in the thickness direction than the carbon nanotubes. Accordingly, when the primer layer is formed using the carbon nanotubes, it is advantageous for securing an electron transfer path between the negative electrode mixture layer and the current collector, and thus has better electron conductivity.

These carbon nanotubes may have a largely bundled type or entangle type structure, and the carbon nanotubes according to the present invention may be included in any shape, but specifically, having a bundled structure desirable.

Specifically, the bundle-type carbon nanotubes and the entanglement-type carbon nanotubes are divided by particle size and shape, and in the chemical vapor deposition method, manufactured by varying the temperature in order to manufacture the carbon nanotubes having a desired shape. can do. At this time, since the carbon nanotube having the entanglement structure is a lumped structure and is similar to an intermediate shape between the dotted conductive material and the carbon nanotube having the bundle structure, network structure formation is disadvantageous, whereas the bundle structure is as described above. Since the carbon atoms are spaced apart from each other by a predetermined distance and exist in strands, electron transfer is easier, and therefore, it is more preferable that the carbon nanotubes included in the primer layer of the present invention have a bundled structure.

In addition, the carbon nanotubes have the most preferable electron transport path and have a diameter and length for further improving conductivity, specifically, a diameter of 0.1 nm to 20 nm, a length of 100 nm to 5 μm, specifically, a length of It may be 100 nm to 2 μm.

Here, the diameter and length can be measured by AFM, and when within the above range, it is more advantageous for the formation of a three-dimensional web-type network structure without increasing the thickness of the primer layer too much, so that electronic conductivity is secured It is more preferable in terms of

Out of the above range, if the diameter is too large, the thickness of the primer layer becomes thicker than necessary, and there is a problem that conductivity is lowered due to poor crystallinity, and when the length is too short, there is a problem in forming a network structure, too When the length exceeds 5 μm, there is a problem in forming a thin and uniform primer layer, which is not preferable.

On the other hand, in the primer layer, in addition to the carbon nanotubes, a first binder for binding the primer layer to the components of the current collector and the negative electrode mixture layer is essential, wherein the content ratio of the carbon nanotubes and the first binder is It may be 1:3 to 3:1 by weight.

In the above range, the most desirable adhesive strength and electronic conductivity are exhibited. Outside the above range, if the amount of carbon nanotubes is too small, the desired degree of electronic conductivity cannot be secured, and if the first binder is too small, a predetermined or higher adhesive strength is secured. However, it is not preferable because it adversely affects not only the lifespan characteristics but also the battery resistance, and it deteriorates overall battery performance including electronic conductivity.

The thickness of the primer layer having such a configuration may be 0.1 μm to 2 μm, specifically 0.1 μm to 1 μm, and more specifically, 0.3 μm to 0.5 μm.

As a component of the primer layer, the present invention does not require a lot of binder for binding it to the current collector because it contains carbon nanotubes with high anisotropy, not a conductive material having a conventional porous structure, and a web-type network Since it is advantageous for structure formation and has excellent electron conductivity in the electrode thickness direction, it does not need to contain a large amount compared to the conventional conductive material. It is possible to secure the electronic conductivity and adhesion to the degree of

Therefore, since a smaller amount of carbon nanotubes and a binder are required to exhibit the same electronic conductivity and adhesion as in the case of applying a primer layer using a conventional conductive material, the thickness of the primer layer can be reduced, which is excellent in terms of energy density per volume A battery can be made, and when the primer layer is formed to the same thickness as the conventional primer layer, better adhesion and electronic conductivity can be exhibited.

However, the above range is most preferable when all of the capacity is considered, and if it is less than 0.1 μm outside the above range, the coating uniformity is deteriorated and the formation of the primer layer is not well made, or the adhesive strength and If electron conductivity cannot be ensured, and when it exceeds 2 μm, a large amount of binder and carbon nanotubes are required in the same way as in the configuration having a conventional primer layer, thereby increasing the manufacturing cost, and when the amount of carbon nanotubes is too large It is undesirable because the conduction path is cut off and the rate characteristics are rather deteriorated, and the overall performance of the battery, such as capacity to volume ratio, is deteriorated because the content of the electrode mixture layer is relatively reduced or increased in volume.

The coating method of the primer layer is not limited to a wet or dry method, and all methods related to conventional electrode coating may be used, but in detail, a wet coating method may be used.

For example, the method is not limited, but may be prepared through gravure-roll coating.

Other carbon nanotubes and a dispersion of the first binder dispersed in a solvent is applied by a coating method such as bar coating, doctor blade coating, spray coating, flow coating, roll coating, spin coating and gravure coating. It can be carried out by a wet coating method. Of course there is In the case of wet coating, drying may be performed after coating the primer layer and the negative electrode mixture layer may be coated, or the negative electrode mixture layer may be coated before drying, but is not limited thereto.

On the other hand, the thickness of the negative electrode mixture layer includes a negative electrode active material exhibiting a substantial capacity, and may be relatively much thicker, specifically, 20 μm to 200 μm, more specifically, 50 μm to 200 μm. can

Out of the above range, if it is less than 20 μm, the capacity is too low to sufficiently perform the role of a secondary battery as electric power, and if it exceeds 200 μm, the thickness of the electrode becomes too thick, and the manufacturing cost is very high It is difficult to secure the electronic conductivity in the mixture layer, and separation occurs in the mixture layer.

The negative active material included in the negative electrode mixture layer is not limited, and for example, crystalline artificial graphite, crystalline natural graphite, amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, Ketjen black, super P, graphene ( graphene), and at least one carbon-based material selected from the group consisting of fibrous carbon, a Si-based material, 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, elements of groups 1, 2, 3 of the periodic table, halogen; 0<x≤1 metal composite oxides such as 1≤y≤3;1≤z≤8); lithium metal; lithium alloy; 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; titanium oxide; Lithium titanium oxide and the like may be included, but specifically, it may be a graphite-based material, more specifically artificial graphite, which is preferable in terms of capacity while exhibiting the greatest effect by application of the primer layer of the present invention.

The content of the second binder included in the negative electrode mixture layer may be reduced by at least 30% or more compared to the case where the primer layer is not applied by the application of the primer layer. In particular, according to the present invention, carbon nano When the primer layer is formed using a tube, the more excellent adhesive force is exhibited by the shape of the conductive carbon, and it can be reduced by up to 40%.

Accordingly, the content of the second binder of the negative electrode mixture layer may be 0.5 to 2.5% by weight, specifically 0.8 to 1.5% by weight, based on the total weight of the negative electrode mixture layer, relative to the content of the negative active material can be increased, thereby exhibiting the effect of improving the capacity of the battery.

The first binder included in the primer layer and the second binder included in the negative electrode mixture layer are not limited as long as they are components that assist in bonding between the active material and the conductive material and bonding to the current collector, for example, polyvinyl fluoride. Leadene, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene Terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc. may be selected respectively, but in detail, in terms of manufacturing easiness and mutual adhesion between the primer layer and the negative electrode mixture layer, ) is more preferably a compound of

Meanwhile, the negative electrode mixture layer may further include an electronically conductive conductive material, and specifically, 0.1 to 5% by weight, specifically, 0.3 to 2% by weight, based on the total weight of the negative electrode mixture layer. The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery as a conventionally known conductive material, for example, carbon black, acetylene black, Ketjen black, channel black, furnace black , carbon black such as lamp black and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, 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 may be used.

In addition, the negative electrode mixture layer may optionally further include a filler or the like.

The filler is optionally used as a component for suppressing the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. For example, an olipine-based polymer such as polyethylene or polypropylene; A fibrous material such as glass fiber or carbon fiber is used.

The present invention also provides a method for manufacturing the negative electrode for the secondary battery, the negative electrode for the secondary battery,

forming a primer layer including carbon nanotubes and a first binder on at least one surface of the anode current collector; and

forming an anode mixture layer including an anode active material and a second binder on the primer layer;

It can be prepared including.

Here, the negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface-treated with carbon, nickel, titanium, silver, etc. on the surface of the aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven body, and the like.

A primer layer and a negative electrode mixture layer are formed on the negative electrode current collector as described above.

At this time, the primer layer and the negative electrode mixture layer may follow a conventional electrode coating method, but is not limited thereto, but the primer layer may be formed by a wet method, for example, a gravure-roll coating method, and the negative electrode mixture The layer may be formed by a wet method in which an electrode slurry obtained by mixing a negative electrode active material and a second binder in a solvent is applied on the primer layer and then dried.

The present invention also provides a lithium secondary battery including the negative electrode for the secondary battery.

The lithium secondary battery may have a structure in which an electrode assembly including the negative electrode, the positive electrode, and the separator is embedded in a battery case together with an electrolyte.

The positive electrode may be manufactured by, for example, applying a positive electrode mixture in which a positive electrode active material and a binder are mixed to a positive electrode current collector, and if necessary, a conductive material and a filler may be further added as described in the negative electrode. .

The positive electrode current collector is generally manufactured to have a thickness of 3 to 201 μm, and is not particularly limited as long as it has high conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium , and carbon, nickel, titanium or silver on the surface of aluminum or stainless steel may be used, and specifically aluminum may be used. The current collector may increase the adhesive force of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, sheet, foil, net, porous body, foam body, and nonwoven body are possible.

The positive active material may include, for example, 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 , LiV 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 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 (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; Although Fe2 _{(MoO4)3 etc. are} mentioned, It is not limited only to these.

Examples of the binder, the conductive material, and the filler are as described in the negative electrode.

The separator may be made of the same material, but is not limited thereto, and may be made of different materials depending on the safety, energy density, and overall performance of the battery cell.

The pore size and porosity of the separator are not particularly limited, but the porosity may be in the range of 10 to 95%, and the pore size (diameter) may be in the range of 0.1 to 50 μm. When the pore size and porosity are less than 0.1 μm and 10%, respectively, it acts as a resistance layer, and when the pore size and porosity exceed 50 μm and 95%, it is difficult to maintain mechanical properties.

The electrolyte may be a lithium salt-containing non-aqueous electrolyte, and the lithium salt-containing non-aqueous electrolyte consists of a non-aqueous electrolyte and a lithium salt, and as the non-aqueous electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc. are used, but these It is not limited to only.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile , nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ions A polymerization agent containing a dissociating group may 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, etc. 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 material 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 ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate, imide, etc. may be used.

In addition, for the purpose of improving charge/discharge characteristics and flame retardancy, nonaqueous electrolytes include, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. have. In some cases, in order to impart incombustibility, a halogen-containing solvent 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, and FEC (Fluoro-Ethylene) Carbonate), PRS (propene sultone), etc. may be further included.

In one specific example, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ Lithium salt such as a cyclic carbonate of EC or PC and a low-viscosity solvent of DEC, DMC or EMC A lithium salt-containing non-aqueous electrolyte may be prepared by adding it to a mixed solvent of linear carbonate.

The present invention provides a battery module including the lithium secondary battery as a unit cell, and a device including the battery module as a power source. Of course, a battery pack including the battery module may be used as a power source for the device.

The device is, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, an MP3, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV) , a Plug-in Hybrid Electric Vehicle (PHEV), an electric bicycle (E-bike), an electric scooter (E-scooter), an electric golf cart, or a system for power storage. However, it is needless to say that the present invention is not limited thereto.

Since the structure and manufacturing method of such a battery module, a battery pack, and a device are known in the art, a detailed description thereof will be omitted herein.

As described above, the negative electrode for a secondary battery according to the present invention includes a primer layer including a carbon nano tube (CNT) and a first binder binding the components between the negative electrode current collector and the negative electrode mixture layer By doing so, the electron transport path between the current collector and the negative electrode mixture layer is secured by forming a web-type network structure in the primer layer, thereby further improving conductivity, and the carbon nanotubes are superior to conventional conductive materials. Since it has high anisotropy and can be coated flat on the current collector, it is advantageous for coating processability and exhibits excellent adhesion even with a thinner thickness. There is an effect that can improve the overall performance of the battery.

Hereinafter, the contents of the present invention will be described in detail through examples, but the following examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

As a binder, CMC, SBR, and bundled CNTs (diameter: 5 nm, length: 1 μm) were mixed at a ratio of 1:10:10 by weight and added to water to prepare a precursor for preparing a primer layer.

An anode slurry was prepared by mixing flake-type artificial graphite as an anode active material, CMC, SBR as a binder, and carbon black as a conductive material in a weight ratio of 96:1:2:1, and adding water as a solvent.

After the primer layer was applied to a thickness of 0.3 μm by a gravure-roll coating method on a copper foil having a thickness of 40 μm, a negative electrode slurry was applied to a thickness of 150 μm. The negative electrode was prepared by rolling to a porosity of 25% and drying at 130° C. under vacuum for about 12 hours.

<Example 2>

An anode was prepared in the same manner as in Example 1, except that intangle-type CNTs (diameter: 10 nm, length: 1.3 μm) were used instead of bundle-type CNTs (diameter: 5 nm, length: 1 μm).

<Example 3>

A cathode was prepared in the same manner as in Example 1, except that bundled CNTs (diameter: 10 nm, length: 5 μm) were used instead of bundled CNTs (diameter: 5 nm, length: 1 μm).

<Example 4>

Flake-type artificial graphite as an anode active material, CMC, SBR as a binder, and carbon black as a conductive material were mixed in a weight ratio of 97: 1: 1: 1, and water was added as a solvent to use a negative electrode slurry. A negative electrode was prepared in the same manner as in Example 1.

<Comparative Example 1>

An anode was prepared in the same manner as in Example 1, except that graphene was used instead of bundled CNTs (diameter: 5 nm, length: 1 μm).

<Comparative Example 2>

An anode was prepared in the same manner as in Example 1, except that acetylene black was used instead of bundled CNTs (diameter: 5 nm, length: 1 μm).

<Comparative Example 3>

A negative electrode was manufactured in the same manner as in Example 1, except that the negative electrode was prepared by applying only the negative electrode slurry without forming a primer layer.

<Comparative Example 4>

A negative electrode was manufactured in the same manner as in Example 1, except that the primer layer was applied to a thickness of 2.5 μm by a gravure-roll coating method on a copper foil having a thickness of 40 μm.

<Comparative Example 5>

Examples except that CMC, SBR, and bundled CNT (diameter: 5 nm, length: 1 μm) as a binder were mixed at 1: 1: 8 by weight and added to water to prepare a precursor for preparing a primer layer A negative electrode was prepared in the same manner as in 1.

<Experimental Example 1>

A positive electrode mixture having a composition of 90% by weight of positive active material (LiCoO ₂ ), 5% by weight of Super-P (conductive material), and 5% by weight of PVDF (binder) was added to NMP (N-methyl-2-pyrrolidone) as a solvent. After preparing a positive electrode slurry, it was coated on an aluminum current collector to prepare a positive electrode.

To the negative electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 4, the positive electrode, a polyethylene film (Celgard, thickness: 20 μm) as a separator, and ethylene carbonate, dimethylene carbonate, and diethyl carbonate were 1: 2 : Secondary batteries were manufactured by using a liquid electrolyte in which LiPF ₆ was dissolved at 1 M in a solvent mixed with 1.

These secondary batteries were subjected to a rate test in a voltage range of 2.5 V to 4.4 V, and the results are shown in Table 1 below.

0.1C/0.1C
vs.
0.1C/0.1C 0.5C/0.5C
vs.
0.1C/0.1C 1C/1C
vs.
0.1C/0.1C 2C/2C
vs.
0.1C/0.1C Example 1 100% 98.8% 96.8% 92.2% Example 2 100% 98.7 96.1 90.6 Example 3 100% 98.1 95.7 84.2 Example 4 100% 99.3 98.1 93.2 Comparative Example 1 100% 97.4 92.4 81.1 Comparative Example 2 100% 98.1 95.2 83.4 Comparative Example 3 100% 96.2 88.3 74.1 Comparative Example 4 100% 98.1 94.6 82.1

Referring to Table 1, when a primer layer including a material having different rate characteristics of a secondary battery using an electrode including a primer layer according to the present invention is used (Comparative Examples 1 and 2), or a primer layer is not used It can be confirmed that excellent properties are exhibited compared to the case (Comparative Example 3).

In addition, when using CNTs having a bundle-type structure (Example 1) than when using CNTs having an entanglement-type structure (Example 2), more excellent properties are exhibited.

Furthermore, referring to Example 3, when the length of the CNT increases to 5 μm, it can be seen that the rate characteristic is deteriorated compared to Example 1, and when the length is too large, it can be seen that the inferiority of the rate characteristic appears. have.

In addition, referring to Example 1 and Comparative Example 4, when the thickness of the primer layer is increased to a certain thickness or more, it can be confirmed that the rate characteristic is rather deteriorated.

Finally, referring to Example 4, as the amount of binder in the negative electrode slurry is increased, the amount of the active material is relatively increased, and thus it can be confirmed that the negative electrode slurry has better rate characteristics.

<Experimental Example 2>

After charging and discharging 200 times at 0.5C using the batteries prepared in Experimental Example 1, the discharge capacity retention rate of 200 times compared to the single discharge capacity was calculated, and the results are shown in Table 2 below.

1 time 200 episodes Example 1 100% 89% Example 2 100% 87 Example 3 100% 86 Example 4 100% 91 Comparative Example 1 100% 75 Comparative Example 2 100% 83 Comparative Example 3 100% 72 Comparative Example 4 100% 81

Referring to Table 2, similarly as shown in Table 1, when a primer layer including a material having different lifespan characteristics of a secondary battery using an electrode including a primer layer according to the present invention is used (Comparative Example 1 and 2), or it can be confirmed that the primer layer is not used (Comparative Example 3) and exhibits superior properties.

In addition, when using the bundle-type CNTs (Example 1) than when using the CNTs having an entanglement-type structure (Example 2), more excellent lifespan characteristics are exhibited.

Furthermore, referring to Example 3, when the length of the CNTs is increased to 5 μm, it can be confirmed that the lifespan characteristics are also deteriorated compared to that of Example 1.

Similarly, when the thickness of the primer layer is increased, the capacity retention rate is also lowered.

Finally, referring to Example 4, it can be confirmed that the life characteristics are more excellent because the amount of the active material is relatively increased as the content of the binder in the negative electrode slurry is increased.

<Experimental Example 3>

In order to measure the peel strength of the negative electrode prepared in Example 1 and Comparative Example 5, the force applied while attaching the electrode surface to the tape at a constant pressure and peeling it off at an angle of 180 degrees was measured. In the case of dry adhesion, the electrode was as it is after rolling, and in the case of wet adhesion, the rolled electrode was immersed in the electrolyte for 24 hours, the Li salt was washed in DMC solvent, and the adhesion was measured after drying for 24 hours, and the results are shown in Table 3 below. indicated.

Dry adhesion Wet adhesion Example 1 28.5 gf 6.5 gf Comparative Example 5 22.6 gf 0.2 gf

Referring to Table 3, it can be seen that when CNT is added in excess of a predetermined content or more, the adhesive force is significantly reduced.

This is because the adhesion of the electrode is affected by the content of the binder, and when the CNT content is excessively added, the content of the binder is relatively decreased. In this case, the rate characteristic may slightly increase, but the adhesive force is significantly reduced, and the active material layer together with the primer layer may be detached in the subsequent charging/discharging process of the battery. .

Those of ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above content.

Claims (20)

negative electrode current collector;
A primer layer formed on at least one surface of the negative electrode current collector and including a carbon nano tube (CNT), and a first binder binding the carbon nano tube, the current collector, and the components of the negative electrode mixture layer below ; and
a negative electrode mixture layer positioned on the primer layer and including a negative active material and a second binder for binding between the negative active material particles;
including,
The carbon nanotubes have a bundled type (aligned type) structure, have a diameter of 0.1 nm to 20 nm, and a length of 100 nm to 2 μm,
The content ratio of the carbon nanotubes and the first binder in the primer layer is 1:3 to 3:1 by weight,
The thickness of the primer layer is 0.3 to 0.5㎛,
A negative electrode for a secondary battery, characterized in that the content of the second binder of the negative electrode mixture layer is 0.5 to 2.5% by weight based on the total weight of the negative electrode mixture layer. delete delete delete delete The negative electrode for a secondary battery according to claim 1, wherein the primer layer is formed by a wet coating method. The negative electrode for a secondary battery according to claim 1, wherein the negative electrode mixture layer has a thickness of 20 μm to 200 μm. The negative electrode for a secondary battery according to claim 1, wherein the negative active material is a graphite-based material. The negative electrode for a secondary battery according to claim 8, wherein the graphite-based material is artificial graphite. delete The negative electrode for a secondary battery according to claim 1, wherein the first binder and the second binder are compounds of the same kind. The negative electrode according to claim 1, wherein the negative electrode mixture layer further comprises an electronically conductive conductive material. The negative electrode for a secondary battery according to claim 12, wherein the content of the conductive material is 0.1 wt% to 5 wt% based on the total weight of the negative electrode mixture layer. forming a primer layer including carbon nanotubes and a first binder on at least one surface of an anode current collector;
forming an anode mixture layer including an anode active material and a second binder on the primer layer;
including,
The carbon nanotubes have a bundled type (aligned type) structure, have a diameter of 0.1 nm to 20 nm, and a length of 100 nm to 2 μm,
The content ratio of the carbon nanotubes and the first binder in the primer layer is 1:3 to 3:1 by weight,
The thickness of the primer layer is 0.3 to 0.5㎛,
The method of manufacturing a negative electrode for a secondary battery, characterized in that the content of the second binder of the negative electrode mixture layer is 0.5 to 2.5% by weight based on the total weight of the negative electrode mixture layer. 15. The method of claim 14, wherein the primer layer is formed by a wet coating method. 15. The method of claim 14, wherein the negative electrode mixture layer is formed by applying an electrode slurry in which an anode active material and a second binder are mixed in a solvent and then dried on a primer layer. delete delete delete delete