KR20170031387A - Electrode Comprising Active Material Layers Having Active Material Particles of Different Average Particle Sizes - Google Patents

Abstract

The present invention relates to an electrode for a secondary battery, comprising: a current collector; a first coating layer formed on at least one surface of the current collector, and including a first active material; and a second coating layer formed on the first coating layer, and including a second active material having the average particle diameter relatively smaller than the first active material.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrode for a secondary battery including active material particles having different average particle diameters,

The present invention relates to an electrode for a secondary battery comprising coating layers having different average particle diameters of active material particles.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

The secondary battery is classified into a cylindrical battery and a prismatic battery in which the electrode assembly is housed in a cylindrical or rectangular metal can according to the shape of the battery case, and a pouch-shaped battery in which the electrode assembly is housed in a pouch-shaped case of an aluminum laminate sheet .

The electrode assembly incorporated in the battery case is a charge / dischargeable power generating element formed of a laminate structure of a positive electrode / separator / negative electrode. The electrode assembly is composed of a jelly-roll type in which a separator is interposed between a positive electrode and a negative electrode coated with an active material, Sized positive and negative electrodes are stacked in a stacked state in a state in which a separator is interposed therebetween.

A full cell or anode / separator / cathode / separator / separator / separator / cathode assembly having a positive electrode / separator / negative electrode structure with a constant unit size, which is a progressive structure of a jelly- A stack / folding type electrode assembly having a structure in which a bicell having a positive (negative) electrode structure is folded by using a continuous long separating film has been developed.

Further, in order to improve the processability of the conventional stacked electrode assembly and meet the demands of various types of secondary batteries, a lamination / stacked electrode structure in which unit cells alternately laminated and laminated are laminated Assemblies have also been developed.

On the other hand, the electrode of the secondary battery has a structure in which an electrode coating layer including an electrode active material and a binder is formed on the current collector. The electrode coating layer is subjected to a rolling process to improve the energy density of the electrode and improve adhesion to the current collector. In recent years, as the demand for high-density secondary batteries increases, the rolling rate of the electrode coating layer is further increased and the loading amount is further increased.

However, in the case of the electrode having a high rolling rate and a large loading amount as described above, the space between the active materials decreases, and it takes a long time for the electrolytic solution to be impregnated into the electrode coating layer and the lithium ion transmission through the electrolyte is difficult, There has been a problem of deterioration.

The surface of the electrode coating layer has a high accessibility of the electrolytic solution and a short migration path of lithium ions, so that the above problem is somewhat small. However, even if rolled with the same force, the porosity decreases more inside than the surface side of the electrode coating layer, and in the case of the inside, the problem of the electrolyte impregnability becomes more remarkable. In addition, the inside of the electrode coating layer has a low accessibility with the electrolyte solution, and the migration path of the lithium ion is long, so that the impregnability drop and the ion transfer rate are more problematic than the surface side.

Therefore, there is a high need for a technique capable of sufficiently securing the electrolyte impregnability and the ion transfer rate even when the energy density is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that, as will be described later, the second active material, which is formed on the first coating layer and contains a second active material having an average particle diameter relatively smaller than that of the first active material, It has been confirmed that the impregnation property and the ion transfer rate of the electrolyte are improved even when the energy density is increased when the coating layer is included, and thus the present invention has been accomplished.

Accordingly, the electrode for a secondary battery according to the present invention comprises: a current collector; A first coating layer formed on at least one surface of the current collector, the first coating layer including a first active material; And a second coating layer formed on the first coating layer and including a second active material having an average particle diameter relatively smaller than that of the first active material.

That is, the second coating layer includes a second active material having a relatively small average particle diameter (D50) to improve the energy density, and the first coating layer including the first active material having a relatively large average particle size has a porosity, Thereby improving the stability and ion transfer rate.

According to the conventional technical knowledge, it is known that it is advantageous to improve the porosity near the surface of the active material coating layer remote from the current collector in order to ensure electrolyte impregnability. In other words, by adapting to the present invention, it was intended to improve the porosity of the second coating layer to improve the electrolyte impregnability. However, according to this technical arrangement, as the rolling rate and the loading amount of the electrode are increased, the porosity of the first coating layer is further reduced as compared with the second coating layer, so that the electrolyte is hardly impregnated in the first coating layer. Therefore, it takes more time to impregnate the entire electrode with the electrolytic solution. Further, the movement path of lithium ions to the first coating layer becomes longer, and the ion transfer rate as a whole is remarkably reduced.

On the other hand, according to the present invention, the second coating layer uses an active material having a high accessibility to the electrolytic solution, a short migration path of lithium ions, and a relatively small average particle size to maintain the electrolyte impregnability and the ion transfer rate . In addition, since the first coating layer can maintain a high porosity by using an active material having a relatively large average particle size, it is possible to improve the impregnating property of the electrolytic solution even if the accessibility of the electrolytic solution is not easy, So that the ion transfer rate can be improved.

That is, the present invention uses a first active material having a relatively large average particle diameter in the first coating layer and a second active material having a relatively small average particle size in the second coating layer, which is contrary to conventional technology, The electrolyte impregnating property and the ion transfer rate are increased.

In one specific example, the average particle size of the first active material may be 1.01 or more to 5 or less, more specifically 1.3 or more to 3 or less, in comparison with the average particle size of the second active material. When the average particle diameter is less than 1.01, If the ratio is more than 5, the energy density of the electrode is decreased and the porosity of the second coating layer is too low, so that the electrolyte impregnability and the ion transfer rate may be decreased.

The average particle size of the first active material may be 1 mu m or more and 50 mu m or less in the range satisfying the size condition relative to the second active material.

The average particle size of the second active material may be 0.5 mu m or more to 40 mu m or less in the range satisfying the size condition relative to the first active material.

In one specific example, the porosity of the first coating layer may be relatively large compared to the porosity of the second coating layer.

Specifically, the porosity of the first coating layer may be 1.01 or more to 3 or less, more specifically 1.1 or more to 2 or less, in relation to the porosity of the second coating layer.

The porosity can be quantified by analyzing the shapes of the active material particles and pores by observing with SEM after cutting the electrode in the cross-sectional direction after manufacturing the electrode.

In one specific example, the second coating layer may further include a third active material having an average particle diameter different from that of the second active material.

The third active material may be larger or smaller than the average particle size of the second active material. By including the third active material, porosity and energy density of the second coating layer can be more finely adjusted. Particularly, when particles having different average particle diameters are mixed, the porosity can be effectively reduced to further improve the energy density.

The average particle size of the third active material may be 0.5 mu m or more to 50 mu m or less in the range satisfying the size condition relative to the second active material.

On the other hand, problems of electrolytic solution impregnation and reduction of ion transmission rate due to an increase in the rolling rate and the loading amount may occur in both the positive electrode and the negative electrode.

In one specific example, the first active material, the second active material, and the third active material are cathode active materials, and in detail, they may be the same cathode active material. In this case, since only one type of cathode active material is manufactured and the electrode according to the present invention can be manufactured only through the classification according to the size, the process can be efficient and the cost can be reduced.

In still another example, the first active material, the second active material, and the third active material are negative active materials, and specifically, they may be the same negative active material. In this case as well, since the electrode according to the present invention can be manufactured only through the process of manufacturing only one type of anode active material and classification according to the size, the process can be efficiently performed and the cost can be reduced.

In one specific example, the thickness of the first coating layer may be the same or different from the thickness of the second coating layer and may be varied to control the energy density, electrolyte impregnability and ion transport rate.

Specifically, the ratio of the thickness of the first coating layer to the thickness of the second coating layer may be in the range of 1: 2 to 2: 1. If the first coating layer is too thin, the electrolyte- The transfer speed is lowered, and if the second coating layer is too thin, the energy density can be reduced.

In one specific example, the loading amount of the first coating layer and the second coating layer as a whole may be 10 mg / cm ² or more to 50 mg / cm ² or less. When the loading amount of the electrode is increased as described above, The electrolyte impregnability of the first coating layer is generally reduced drastically. However, according to the present invention, the porosity of the first coating layer can be ensured and the electrolyte impregnability can be further improved.

The thickness of the first coating layer and the second coating layer may be 100 mu m or more and 300 mu m or less. When the thickness of the electrode is increased, the electrolyte impregnability of the first coating layer is sharply decreased as compared with the second coating layer. However, according to the present invention, the porosity of the first coating layer is ensured, The impregnability of the electrolyte solution can be further improved.

In one specific example, the first coating layer and the second coating layer may each further comprise a binder and a dispersing agent.

The dispersant is not particularly limited as long as it improves the dispersibility of the electrode active material and does not significantly deteriorate the adhesive force. Examples of the dispersant include an oil soluble polyamine, an oil-soluble amine compound, fatty acids, fatty alcohols, And sorbitan fatty acid esters, and the like.

The present invention also provides a method of manufacturing an electrode for a secondary battery,

(a) applying a first slurry containing a first active material and a solvent on at least one surface of a current collector;

(b) applying a second slurry containing a second active material and a solvent having an average particle diameter relatively smaller than that of the first active material on the first slurry in an undried state applied to the current collector;

(c) drying the first slurry and the second slurry applied to the current collector to form a first coating layer and a second coating layer; And

(d) rolling the first coating layer and the second coating layer;

. ≪ / RTI >

Since the first slurry and the second slurry do not have to be respectively dried through the process of applying the second slurry on the first slurry in an undried state as in the process (b), only one drying step is required, Can be simplified.

Further, the second slurry coated on the first slurry in an undried state may be partially mixed at the interface, and the bonding force between the first coating layer and the second coating layer may be further increased after drying.

In another example, a method of manufacturing an electrode for a secondary battery includes:

(A) applying a first slurry containing a first active material and a solvent on at least one surface of a current collector, and drying the first slurry to form a first coating layer;

(B) forming a second coating layer on the first coating layer by applying a second slurry containing a second active material and a solvent having an average particle diameter relatively smaller than that of the first active material, and drying the second slurry; And

(C) rolling the first coating layer and the second coating layer;

. ≪ / RTI >

When the second slurry is applied after the first coating layer is formed as in the above processes (A) and (B), uniform application of the second slurry is possible.

The present invention also provides an electrode assembly including the electrode, wherein the electrode assembly is embedded in a battery case together with an electrolyte solution.

Hereinafter, other components of the secondary battery will be described.

The secondary battery includes a positive electrode, a negative electrode, and a separator. The positive electrode may be manufactured by, for example, applying a positive electrode mixture mixed with a positive electrode active material, a conductive material, and a binder to a positive electrode collector, A filler may further be added to the positive electrode mixture.

The cathode current collector is generally formed to a thickness of 3 to 201 탆 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 a surface treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel can be used. Specifically, aluminum can be used. The current collector may form fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where 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, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode material mixture containing the positive electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery, and examples thereof include graphite, carbon black, acetylene black, ketjen black, channel black, perneic black, lamp black, Carbon black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder contained in the positive electrode is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the positive electrode active material, as a component that assists in bonding between the active material and the conductive material and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

On the other hand, the negative electrode may be manufactured by applying a negative electrode mixture containing a negative electrode active material and a binder to a negative electrode collector, and may further include a dispersant, a filler, and the like selectively.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

In the present invention, the thickness of the anode current collector may be the same within the range of 3 to 201 [mu] m, but may have different values depending on the case.

The negative electrode active material may be, for example, natural graphite and artificial graphite, Li _x Fe ₂ O _{3 (0? X ? 1), Lix} WO ₂ (0? _X? 1), Sn _x Me _1-x Me _{y O z (Me: Mn, Fe} , Pb, Ge; Me ': Al, B, P, Si, Group 1 of the Periodic Table, Group 2, Group 3 element, a halogen; 0 <x≤1;1≤y≤3; 1? Z? 8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{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 Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, or the like may be used.

In one specific example, the separation membrane may be a polyolefin-based film commonly used in the art, and may be, for example, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyetheretherketone, A sheet made of at least one selected from the group consisting of polyethersulfone, polyphenylene oxide, polyphenylenesulfrode, polyethylene naphthalene, and mixtures thereof.

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

The pore size and porosity of the separation membrane are not particularly limited, but the porosity may be in the range of 10 to 95% and the pore size (diameter) may be 0.1 to 50 탆. When the pore size and porosity are 0.1 μm or less and 10% or less, respectively, it acts as a resistive layer. If the pore size and porosity are more than 50 μm and 95%, it is difficult to maintain the mechanical properties.

The electrolyte solution may be a non-aqueous electrolyte containing a lithium salt, and the non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. Non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, The present invention is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile , Nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride A polymer containing an acid dissociation group and the like 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a substance that is soluble in the nonaqueous electrolyte and includes, 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 carboxylate lithium, lithium tetraphenylborate, and imide.

The nonaqueous electrolyte may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added have. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing nonaqueous electrolyte.

The present invention also provides a battery pack including such a secondary battery as a unit cell, and a device including such a battery pack as a power source.

The device may be, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, 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 bike (E-bike), an electric scooter (E-scooter), an electric golf cart, However, the present invention is not limited thereto.

The structure and manufacturing method of such a device are well known in the art, so a detailed description thereof will be omitted herein.

As described above, the electrode for a secondary battery according to the present invention is formed on a current collector and includes a first coating layer including a first active material, and a second coating layer formed on the first coating layer, And a second coating layer including a second active material having a small average particle size, thereby improving the electrolyte density and ion transfer rate while improving the energy density.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but it should be understood that the scope of the present invention is not limited thereto.

&Lt; Example 1 >

Artificial graphite was classified as a negative electrode active material to prepare a first negative electrode active material having an average particle diameter of about 24.1 占 퐉. A first negative electrode slurry was prepared by mixing CMC-Na as a first negative electrode active material, an acrylic binder, and a dispersant at a ratio of 97.0: 1.5: 1.5 based on the weight, and adding water as a solvent.

Artificial graphite was classified as a negative electrode active material to prepare a second negative electrode active material having an average particle diameter of about 12.9 탆. A second negative electrode slurry was prepared by mixing CMC-Na as a second negative electrode active material, an acrylic binder, and a dispersant at a ratio of 97.0: 1.5: 1.5 based on weight, and adding water as a solvent.

A first negative electrode slurry was coated on a copper foil having a thickness of 10 탆 and dried to form a first negative electrode coating layer and a second negative electrode slurry was coated on the first negative electrode coating layer to have the same thickness and dried to form a second negative electrode coating layer Respectively. The first negative electrode coating layer and the second negative electrode coating layer were rolled using a pressure roller, and the total thickness after rolling was 139 占 퐉, respectively. At this time, the total loading amount of the first negative electrode coating layer and the second negative electrode coating layer was 11.1 mg / cm ² .

&Lt; Comparative Example 1 &

As the negative electrode active material, artificial graphite was prepared with an average particle size of about 17.7 탆 without classification. The negative electrode active material, the acrylic binder, and CMC-Na as a dispersant were mixed in a weight ratio of 97.0: 1.5: 1.5, and water was added as a solvent to prepare a negative electrode slurry.

A negative electrode slurry prepared on a copper foil having a thickness of 10 탆 was applied and dried to form a negative electrode coating layer. The anode coating layer was rolled using a pressure roller, and the total thickness after rolling was 140 탆. At this time, the loading amount of the negative electrode coating layer was 11.1 mg / cm ² .

&Lt; Example 2 >

LiCoO ₂ was classified as a cathode active material to prepare a first cathode active material having an average particle diameter of about 18.9 μm. (Kureha KF9706), a dispersant (Zeon BM-740H), and a conductive agent (LGC CNT) were mixed in a weight ratio of 99.0: 0.7: 0.05: 025, (NMP) was added to prepare a first positive electrode slurry.

LiCoO ₂ was classified as a cathode active material to prepare a second cathode active material having an average particle diameter of about 10.9 μm. (Kureha KF9706), a dispersant (Zeon BM-740H), and a conductive agent (LGC CNT) were mixed in a weight ratio of 99.0: 0.7: 0.05: 025, (NMP) was added to prepare a second positive electrode slurry.

A first anode coating layer was formed by applying a first cathode slurry to an aluminum foil having a thickness of 12 占 퐉 and dried to form a second anode coating layer having the same thickness on the first anode coating layer and dried to form a second anode coating layer Respectively. The first anode coating layer and the second anode coating layer were rolled using a pressure roller, and the total thickness after rolling was 114 탆. At this time, the total loading amount of the first anode coating layer and the second anode coating layer was 20.9 mg / cm ² .

&Lt; Comparative Example 2 &

LiCoO ₂ was prepared as a cathode active material with a mean particle diameter of about 14.9 μm without classification. (Kureha KF9706), a dispersant (Zeon BM-740H), and a conductive agent (LGC CNT) were mixed in a ratio of 99.0: 0.7: 0.05: 025 by weight and N-methylpyrrolidone NMP) was added to prepare a positive electrode slurry.

A positive electrode slurry prepared on an aluminum foil having a thickness of 12 占 퐉 was applied and dried to form a positive electrode coating layer. The anode coating layer was rolled using a pressure roller, and the total thickness after rolling was 114 탆. At this time, the total loading amount of the anode coating layer was 20.9 mg / cm ² .

<Experimental Example 1>

The time required for the impregnation of the PC was measured using a propylene carbonate (PC) drop test on the electrodes prepared in Examples 1 and 2 and Comparative Examples 1 and 2. A total of 0.1 ml of PC drop was dropped on the electrode surface and the time from when the PC was dropped to when the PC was completely impregnated was measured.

Impregnation time (sec) Example 1 121 Comparative Example 1 189 Example 2 561 Comparative Example 2 647

Referring to Table 1, in Example 1, the time required for impregnation was reduced by 68 seconds as compared with Comparative Example 1, and the time required for impregnation was reduced by 86 seconds in Example 2 as compared with Comparative Example 2. Based on the time required for impregnation, it can be seen that the electrolyte according to the present invention has improved impregnability by about 30% or more and the anode has improved electrolyte impregnation by about 10% or more.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (23)

Collecting house;
A first coating layer formed on at least one surface of the current collector, the first coating layer including a first active material; And
A second coating layer formed on the first coating layer and including a second active material having an average particle diameter relatively smaller than that of the first active material;
And the second electrode is formed on the second electrode. The electrode for a secondary battery according to claim 1, wherein an average particle diameter of the first active material with respect to an average particle diameter of the second active material is 1.01 or more to 5 or less. The electrode for a secondary battery according to claim 1, wherein an average particle diameter of the first active material is 1.3 or more to 3 or less with respect to an average particle diameter of the second active material. The electrode for a secondary battery according to claim 1, wherein the average particle size of the first active material is in the range of 1 占 퐉 or more to 50 占 퐉 or less in the range satisfying the size requirement relative to the second active material. The secondary battery electrode according to claim 1, wherein the average particle size of the second active material is 0.5 占 퐉 or more to 40 占 퐉 or less within a range satisfying a size condition relative to the first active material. The electrode for a secondary battery according to claim 1, wherein the porosity of the first coating layer is relatively larger than the porosity of the second coating layer. The secondary battery electrode according to claim 6, wherein the first coating layer has a porosity of 1.01 or more to 3 or less, with respect to the porosity of the second coating layer. The secondary battery electrode according to claim 6, wherein the first coating layer has a porosity of 1.1 or more to 2 or less, with respect to a porosity of the second coating layer. The electrode for a secondary battery according to claim 1, wherein the second coating layer further comprises a third active material having an average particle diameter different from that of the second active material. 10. The electrode for a secondary battery according to claim 9, wherein an average particle size of the third active material is 0.5 mu m or more to 50 mu m or less in a range satisfying a relative size condition with respect to the second active material. The secondary battery electrode according to claim 9, wherein the first active material, the second active material, and the third active material are cathode active materials, and more specifically, the same cathode active material. The electrode for a secondary battery according to claim 9, wherein the first active material, the second active material, and the third active material are negative active materials, and more specifically, the same negative active material. The electrode for a secondary battery according to claim 1, wherein the thickness of the first coating layer is equal to or different from the thickness of the second coating layer. The electrode for a secondary battery according to claim 1, wherein the ratio of the thickness of the first coating layer to the thickness of the second coating layer is in the range of 1: 2 to 2: 1. The electrode for a secondary battery according to claim 1, wherein the loading amount of the first coating layer and the second coating layer is 10 mg / cm ² or more to 50 mg / cm ² or less. The secondary battery electrode according to claim 1, wherein the thickness of the first coating layer and the second coating layer is 100 mu m or more and 300 mu m or less. The electrode for a secondary battery according to claim 1, wherein the first coating layer and the second coating layer each further comprise a binder and a dispersant. A method of manufacturing an electrode for a secondary battery,
(a) applying a first slurry containing a first active material and a solvent on at least one surface of a current collector;
(b) applying a second slurry containing a second active material and a solvent having an average particle diameter relatively smaller than that of the first active material on the first slurry in an undried state applied to the current collector;
(c) drying the first slurry and the second slurry applied to the current collector to form a first coating layer and a second coating layer; And
(d) rolling the first coating layer and the second coating layer;
&Lt; / RTI &gt; A method of manufacturing an electrode for a secondary battery,
(A) applying a first slurry containing a first active material and a solvent on at least one surface of a current collector, and drying the first slurry to form a first coating layer;
(B) forming a second coating layer on the first coating layer by applying a second slurry containing a second active material and a solvent having an average particle diameter relatively smaller than that of the first active material, and drying the second slurry; And
(C) rolling the first coating layer and the second coating layer;
&Lt; / RTI &gt; An electrode assembly comprising an electrode according to claim 1. The secondary battery according to claim 20, wherein the electrode assembly is embedded in the battery case together with the electrolyte solution. A battery pack comprising a secondary battery according to claim 21 as a unit cell. 23. A device comprising the battery pack according to claim 22 as a power source.