WO2017082680A1 - Anode active material and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to an anode active material comprising a mixture of a first anode active material and a second anode active material, wherein the first anode active material has a hardness of 1 kg/mm² to 10 kg/mm² on the basis of the Vickers hardness standard, and the second anode active material has a higher hardness than the first anode active material. The anode active material according to the present invention comprises a mixture of a first anode active material and a second anode active material having different hardness so that pores of an active material layer are maintained in spite of a rolling process at the time of producing an anode, and the pores acting as an electrolyte flow passage of an electrode can effectively be secured, thereby producing a lithium secondary battery having excellent battery performance by lowering resistance when a battery is charged or discharged.

Description

Anode active material and lithium secondary battery comprising same

[Cross-cited with Related Applications]

This application claims the benefit of priority based on Korean Patent Application No. 10-2015-0158421 filed on November 11, 2015 and Korean Patent Application No. 10-2016-0148664 filed on November 09, 2016. All content disclosed in the literature is included as part of this specification.

[Technical Field]

The present invention relates to a negative electrode active material and a lithium secondary battery including the same, and more particularly, to include a mixture of the negative electrode active material of different hardness, the negative electrode active material and lithium containing the same to more effectively secure the voids as the flow path of the electrolyte solution of the electrode It relates to a secondary battery.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among them, 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.

Lithium metal has been used as a negative electrode of a conventional secondary battery, but the reversal of intercalation of lithium ions while maintaining structural and electrical properties while being known for a battery short circuit due to dendrite formation and the risk of explosion due to this is known ) And replaceable carbon-based compounds.

The carbon-based compound has a very low discharge potential of about -3 V relative to the standard hydrogen electrode potential, and has excellent electrode life due to the very reversible charge and discharge behavior due to the uniaxial orientation of the graphite layer. Indicates. In addition, since the electrode potential during Li ion charging may represent a potential similar to that of pure lithium metal as 0 V Li / Li ⁺ , there is an advantage that higher energy can be obtained when configuring an oxide-based anode and a battery.

In the negative electrode for a secondary battery using the carbon-based compound, a conductive material and a binder are usually mixed with a carbon-based compound as a negative electrode active material to prepare a negative electrode active material slurry, and then the slurry is applied to an electrode current collector such as copper foil. It is manufactured by the method of apply | coating and drying, At the time of the said slurry application | coating, an active material powder is crimped | bonded to an electrical power collector, and a press process is performed in order to make thickness of an electrode uniform.

At this time, as the active material powder is pressed during the rolling process, the space between the active materials is reduced, thereby reducing the pore. As the void is reduced, the penetration of the electrolyte becomes difficult, so that a lot of resistance is required during charging and discharging. .

In particular, this phenomenon is further exacerbated when the electrode thickness is thick, and as the impregnation of the electrolyte to the inside of the electrode becomes difficult, the ion migration path cannot be secured, and thus the ion migration cannot be smoothly performed. Will result.

Therefore, development of a technology capable of securing voids in the negative electrode active material layer is required despite the rolling process in the negative electrode manufacturing process.

The problem to be solved of the present invention is to provide a new negative electrode active material, which can secure the voids of the negative electrode active material layer in spite of the rolling process in the production of the negative electrode of the lithium secondary battery.

Another object of the present invention is to provide a negative electrode including the negative electrode active material and a lithium secondary battery including the same.

In order to solve the above problems, the present invention is a negative electrode active material including a mixture of the first negative electrode active material and the second negative electrode active material, the hardness of the first negative electrode active material is based on Vicker hardness of 1 kg / mm ² to 10 kg / mm ² The second negative electrode active material provides a negative electrode active material having a higher hardness than the first negative electrode active material.

In addition, the present invention provides a negative electrode including the negative electrode active material and a lithium secondary battery including the same in order to solve the other problem.

The negative electrode active material according to the present invention includes a mixture of the first negative electrode active material and the second negative electrode active material having different hardness, and maintains the voids in the active material layer despite the rolling process in the production of the negative electrode, thereby providing a void as the electrolyte flow passage of the electrode. Since it can be effectively ensured, the lithium secondary battery excellent in battery performance can be manufactured by lowering the resistance at the time of charge / discharge of a battery.

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

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

The negative electrode active material according to the present invention is a negative electrode active material including a mixture of a first negative electrode active material and a second negative electrode active material, wherein the second negative electrode active material has a higher hardness than the first negative electrode active material.

Since the negative electrode active material according to the present invention includes a second negative electrode active material having a higher hardness than the first negative electrode active material, when the negative electrode is manufactured, the second negative electrode having a relatively high hardness when pressed to the current collector through a rolling process By maintaining the shape of the active material as much as possible, it is possible to prevent the negative electrode active material contained in the negative electrode active material layer is excessively pressed, thereby reducing the size of the voids in the negative electrode active material layer.

The hardness of the first negative electrode active material may be 1 kg / mm ² to 10 kg / mm ² based on Vicker hardness, specifically 2 kg / mm ² to 9 kg / mm ² , more specifically 5 kg / mm ^{May be from 2} to 8 kg / mm ² .

The second negative electrode active material has a higher hardness than the first negative electrode active material, and the hardness of the second negative electrode active material may be 11 kg / mm ² to 10,000 kg / mm ² based on Vicker hardness, and specifically 20 kg / mm ^It may be ² to 7,000 kg / mm ² , more specifically 100 kg / mm ² to 5,000 kg / mm ² It can be.

The first negative electrode active material and the second negative electrode active material may be mixed in a weight ratio of 99: 1 to 50:50, specifically 95: 5 to 60:40, and more specifically 90:10 to 70:30 Can be.

When the first negative electrode active material and the second negative electrode active material are mixed in a weight ratio of 99: 1 to 50:50, when the negative electrode is pressed to the current collector through a rolling process, the voids of the negative electrode active material layer may be more appropriately maintained. The characteristics of the first negative electrode active material as the active material can be appropriately expressed and maintained.

The first negative electrode active material may be an active material having a relatively low hardness compared to the second negative electrode active material, in which lithium ions may be occluded and released, and may be, for example, soft carbon or hard carbon. Natural graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, petroleum and It may be at least one selected from the group consisting of petroleum or coal tar pitch derived cokes, Al, Zn, Sb, Si, Ge, and Sn, and specifically, may be natural graphite.

The second negative electrode active material may be an active material having a relatively higher hardness than the first negative electrode active material, in which lithium ions may be occluded and released, for example, artificial graphite, metal carbide, alloys, metal oxides, and metal oxides. It may be at least one selected from the group consisting of a metal coated with.

In one example of the present invention, when the second negative electrode active material is artificial graphite, alloy, or metal carbide, it may be used as it is, but may be used by further forming a coating layer of a metal oxide on the surface if necessary. That is, the second negative electrode active material may have a coating layer of metal oxide on the surface of artificial graphite, an alloy, or metal carbide, in which case, the hardness of the active material may be further increased.

The coating layer of the metal oxide formed on the surface of the second negative electrode active material may include droplet coating, chemical vapor deposition, melt coating, electrodynamic coating, and electrospraying. ), Electrospinning or dip coating.

The coating layer may have a thickness of 1 nm to 100 μm, specifically 5 nm to 10 μm, and more specifically 10 nm to 1 μm.

The metal may be at least one selected from the group consisting of Si, Ge, Sn, Al, Zn, and Sb, and the alloy is at least two alloys selected from the group consisting of Si, Ge, Sn, Al, Zn, and Sb. Can be.

The metal carbide is titanium carbide, aluminum carbide, aluminum carbide, chromium carbide, zinc carbide, zinc carbide, copper carbide, magnesium carbide, zirconium carbide, zirconium carbide carbides, molybdenum carbides, vanadium carbides, vanadium carbides, niobium carbides, iron carbides, manganese carbides, cobalt carbides, nickel carbides ( nickel carbide, and tantalum carbide.

The metal oxide is not particularly limited as long as it is a metal oxide, but may be an oxide of a transition metal used as a negative electrode active material of a lithium secondary battery.

The metal oxide is, for example, titanium oxide, aluminum oxide, chromium trioxide, zinc oxide, zinc oxide, copper oxide, magnesium oxide, zirconium Zirconium dioxide, molybdenum trioxide, vanadium pentoxide, niobium pentoxide, iron oxide, manganese oxide, vanadium oxide oxinde), cobalt oxide (cobalt oxide), nickel oxide (nickel oxide), and tantalum pentoxide (tantalum pentoxide) may be one or more selected from the group consisting of, specifically titanium oxide, iron oxide, cobalt oxide and nickel oxide It may be one or more selected from the group consisting of.

When the second negative electrode active material is subjected to a pressure of 2,000 kgf / cm ² , the particle size in the direction in which the pressure is applied may be 60% or more based on the original particle size, specifically 70 to 95%, more specifically As may be having a size of 80 to 90%.

The first negative electrode active material may have an average particle diameter (D ₅₀ ) of 10 nm to 100 μm, and specifically, may have an average particle diameter of 100 nm to 50 μm, more specifically 1 μm to 30 μm.

When the average particle diameter of the first negative electrode active material is 10 nm to 100 μm, the slurry may be appropriately coated with a uniform thickness to prevent the electrode density from lowering and have an appropriate volume / volume, while forming an electrode.

The second negative electrode active material may have an average particle diameter (D ₅₀ ) of 10 nm to 100 μm, and specifically, may have an average particle diameter of 100 nm to 50 μm, more specifically 1 μm to 30 μm.

When the average particle diameter of the second negative electrode active material is 10 nm to 100 μm, the second negative electrode active material may prevent the first active material from being pressed through the rolling process, thereby reducing the voids in the negative electrode active material layer, and at an appropriate electrode density. As a result, it may have a capacity per volume, and the slurry for forming the electrode may be appropriately coated with a uniform thickness.

The second negative electrode active material may have a particle size slightly larger than that of the first negative electrode active material so as to properly maintain the voids of the negative electrode active material layer when the negative electrode active material is pressed into the current collector through a rolling process in manufacturing the negative electrode, and the first negative electrode active material and The ratio of the particle size of the second negative electrode active material may be 1: 1.1 to 1: 5, specifically 1: 1.1 to 1: 2, and more specifically 1: 1.2 to 1: 2.

In the present invention, the average particle diameter (D ₅₀ ) of the first negative electrode active material and the second negative electrode active material may be defined as a particle size based on 50% of the particle size distribution. The average particle diameter is not particularly limited, but may be measured using, for example, a laser diffraction method or a scanning electron microscope (SEM) photograph. In general, the laser diffraction method can measure a particle diameter of about several mm from the submicron region, and a result having high reproducibility and high resolution can be obtained.

In addition, the present invention provides a negative electrode including a negative electrode active material layer including the negative electrode active material.

The negative electrode is prepared by mixing and stirring a solvent, a binder and a conductive material as necessary in the negative electrode active material to prepare a slurry, applying the same to a current collector, compressing and drying the same, and forming a negative electrode active material layer on the current collector. can do.

The anode active material layer may have a porosity of 10 to 60%, specifically 20 to 40%, more specifically may have a porosity of 25 to 35%.

The negative electrode current collector is generally made to a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include carbon, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and carbon on the surface of copper or stainless steel. Surface-treated with nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The binder and the conductive material used for the negative electrode may be used that can be commonly used in the art.

Solvents for forming the negative electrode include an organic solvent such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide or water, and these solvents alone or in combination of two or more. Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the negative electrode active material, the binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The binder may be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride), polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid and polymers in which hydrogen thereof is replaced with Li, Na or Ca, or the like, or Various kinds of binder polymers such as various copolymers can be used.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, farnes black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powders; Conductive whiskers 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.

According to an embodiment of the present invention, the negative electrode may further include a thickener for viscosity control. The thickener may be a cellulose-based compound, for example, may be at least one selected from the group consisting of carboxy methyl cellulose (CMC), hydroxy methyl cellulose, hydroxy ethyl cellulose, and hydroxy propyl cellulose, specifically carboxy methyl cellulose (CMC), and the negative electrode active material and the binder can be applied to the negative electrode by dispersing in water with a thickener.

In addition, the present invention provides a lithium secondary battery including the negative electrode.

The lithium secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode.

The positive electrode can be prepared by conventional methods known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant in a positive electrode active material, and then applying (coating) to a current collector of a metal material, compressing, and drying the positive electrode to prepare a positive electrode. have.

The current collector of the metallic material is a highly conductive metal, and is a metal to which the slurry of the positive electrode active material can easily adhere, and is particularly limited as long as it has high conductivity without causing chemical change in the battery in the voltage range of the battery. For example, surface treated with carbon, nickel, titanium, silver, or the like on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel may be used. In addition, fine concavities and convexities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. The current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, and may have a thickness of 3 to 500 μm.

In the method of manufacturing a lithium secondary battery of the present invention, the positive electrode active material is, for example, lithium cobalt oxide (LiCoO ₂ ); Lithium nickel oxide (LiNiO ₂ ); Li [Ni _a Co _b Mn _c M ¹ _d ] O ₂ (wherein M ¹ is any one selected from the group consisting of Al, Ga, and In or two or more elements thereof, and 0.3 ≦ a <1.0, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.1, a + b + c + d = 1); Li (Li _e M ² _{fe-f '} M ³ _f' ) O _{2 - g} A _g (wherein 0≤e≤0.2, 0.6≤f≤1, 0≤f'≤0.2, 0≤g≤0.2 , M ² includes at least one selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn and Ti, M ³ is 1 selected from the group consisting of Al, Mg and B At least one species, and A is at least one species selected from the group consisting of P, F, S and N), or a compound substituted with one or more transition metals; _{Li 1 + h Mn 2 - h} O 4 ( wherein 0≤h≤0.33), LiMnO _3, the lithium manganese oxide such as LiMn ₂ O _3, LiMnO _2; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , Cu ₂ V ₂ O _7, and the like; Formula ^{_{LiNi 1 - i M 4 i O}} 2 Ni site type lithium nickel oxides represented by (wherein, M = ^4, and Co, Mn, Al, Cu, Fe, Mg, B or Ga, 0.01≤y≤0.3); Formula LiMn _{2 - j} M ⁵ _j O ₂ (wherein M ⁵ = Co, Ni, Fe, Cr, Zn or Ta, 0.01 ≦ _y ≦ 0.1) or Li ₂ Mn ₃ M ⁶ O ₈ (wherein M ⁶ = lithium manganese composite oxide represented by Fe, Co, Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; LiFe ₃ O ₄ , Fe ₂ (MoO ₄ ) _3, etc. may be mentioned, but is not limited thereto.

Solvents for forming the positive electrode include organic solvents such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide or water, and these solvents alone or in combination of two or more. Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the positive electrode active material, the binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The binder may be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride), polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), Sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid and polymers in which hydrogen thereof is replaced with Li, Na or Ca, or the like, or Various kinds of binder polymers such as various copolymers can be used.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, farnes black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powders; Conductive whiskers 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 dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

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

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

Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. no.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, square, pouch type, or coin type using a can.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited to these Examples and Experimental Examples. Embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1

96.3 Weight of the negative electrode active material which mixed natural graphite (particle size 20 micrometers, hardness 7 kg / mm <^2> ) as a 1st active material, and titanium oxide (particle diameter 10 micrometers, hardness 700 kg / mm <^2> ) as a 2nd active material in 50:50 weight ratio. %, Super-p 1.0 wt% as a conductive material, and a mixture of 1.5 wt% and 1.2 wt% of styrene butadiene rubber (SBR) and carboxymethylcellulose (CMC) as a binder, respectively, was added to NMP as a solvent to prepare a negative electrode active material slurry. Was prepared. The prepared negative electrode active material slurry was coated on one surface of a copper current collector to a thickness of 65 μm to form an active material layer to a loading amount shown in Table 1 below, dried, and then rolled to have a porosity of 30% of the active material layer. After that punched to a predetermined size to prepare a negative electrode.

Example 2

A negative electrode was manufactured in the same manner as in Example 1, except that the porosity of the active material layer was 25%.

Example 3

A negative electrode was manufactured in the same manner as in Example 1, except that the porosity of the active material layer was rolled to 20%.

Example 4

In Example 1, except that natural graphite as the first active material and titanium oxide as the second active material were mixed at a weight ratio of 70:30 to be used as the negative electrode active material, and the loading amounts shown in Table 1 below, A negative electrode was manufactured by the same method as 1.

Example 5

A negative electrode was manufactured in the same manner as in Example 4, except that the porosity of the active material layer was 25%.

Example 6

A negative electrode was manufactured in the same manner as in Example 4, except that the porosity of the active material layer was 20%.

Example 7

Sn (particle size 20 μm, hardness 7 kg / mm ² ) coated with 1 wt% iron oxide (Fe ₂ O ₃ ) as the first active material (particle size 10 μm, hardness 100 kg / mm ² ) 96.3 wt% of the negative electrode active material mixed at a weight ratio of 50:50, 1.0 wt% super-p as the conductive material, and 1.5 wt% and 1.2 wt% of styrenebutadiene rubber (SBR) and carboxymethylcellulose (CMC), respectively, as a binder. The mixed mixture was added to NMP as a solvent to prepare a negative electrode active material slurry. The prepared negative electrode active material slurry was coated on one surface of a copper current collector so as to have a loading amount shown in Table 1 below to form an active material layer, dried, and then rolled to have a porosity of 30% of the active material layer. Punching produced a negative electrode.

Example 8

In Example 7, except that 5 wt% of iron oxide coated Sn (particle size 10 μm, hardness 500 kg / mm ² ) was used as the second active material so as to have a loading amount shown in Table 1 below. A negative electrode was manufactured in the same manner as in Example 7.

Example 9

As a first electrode active material of natural graphite (particle diameter 20 ㎛, hardness of 7 kg / mm ²⁾ and the artificial graphite as the second active material (particle size 10 ㎛, hardness of 13 kg / mm ²⁾ a cathode active material mixed in a weight ratio of 50:50 96.3 parts by weight %, Super-p 1.0 wt% as a conductive material, and a mixture of 1.5 wt% and 1.2 wt% of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as a binder, respectively, was added to NMP as a solvent to prepare a negative electrode active material slurry. Was prepared. The prepared negative electrode active material slurry was coated on one surface of a copper current collector so as to have a loading amount shown in Table 1 below to form an active material layer, dried, and then rolled to have a porosity of 30% of the active material layer. Punching produced a negative electrode.

Example 10

A negative electrode was manufactured in the same manner as in Example 9, except that the porosity of the active material layer was 25%.

Example 11

A negative electrode was manufactured in the same manner as in Example 9, except that the porosity of the active material layer was 20%.

Comparative Example 1

96.3% by weight of natural graphite (particle size 20 μm, hardness 7 kg / mm ² ) as the negative electrode active material, 1.0% by weight of super-p as a conductive material, and styrene butadiene rubber (SBR) and carboxymethylcellulose (CMC) as a binder, respectively 1.5 A negative electrode active material slurry was prepared by adding a mixture of wt% and 1.2 wt% to NMP as a solvent.

The prepared negative electrode active material slurry was coated on one surface of a copper current collector so as to have a loading amount shown in Table 1 below to form an active material layer, dried, and then rolled to have a porosity of 30% of the active material layer. Punching produced a negative electrode.

Comparative Example 2

A negative electrode was manufactured in the same manner as in Comparative Example 1 except that the porosity of the active material layer was 25%.

Comparative Example 3

A negative electrode was manufactured in the same manner as in Comparative Example 1 except that the porosity of the active material layer was rolled to 20%.

In the Examples and Comparative Examples, the hardness is a value expressed on the basis of Vicker hardness.

Examples 1-1 to 9-1: Preparation of Lithium Secondary Battery

Li metal was used as a counter electrode, and a polyolefin separator was interposed between each of the negative electrodes and Li metals prepared in Examples 1 to 9, and then ethylene carbonate (EC) and diethyl carbonate (DEC) were added. Coin-type half cells were prepared by injecting an electrolyte in which 1M LiPF ₆ was dissolved in a solvent mixed at a volume ratio of: 70.

Comparative Examples 1-1 to 3-1: Fabrication of Lithium Secondary Battery

Li metal was used as a counter electrode, and a polyolefin separator was interposed between each of the negative electrodes and Li metals prepared in Comparative Examples 1 to 3, and then ethylene carbonate (EC) and diethyl carbonate (DEC) were added. Coin-type half cells were prepared by injecting an electrolyte in which 1M LiPF ₆ was dissolved in a solvent mixed at a volume ratio of: 70.

Experimental Example 1

Using a roll press for each of titanium oxide (hardness 700 kg / mm ² ) or iron oxide coated Sn (hardness 500 kg / mm ² ) used as the second active material in Examples 1 to 6 and 8, respectively. After applying a pressure of 2,000 kgf / cm ² , the average particle diameter (D ₅₀ ) was measured and compared with the average particle diameter (D ₅₀ ) before the pressure was applied.

As a result, in the case of titanium oxide (hardness 700 kg / mm ² ), the average particle diameter (D ₅₀ ) after applying a pressure of 2000 kgf / cm ² is 87% based on the average particle diameter (D ₅₀ ) before the pressure is applied. receive naeteumyeo, iron oxide, a Sn (hardness of 500 kg / mm ²⁾ is 2000 kgf / average particle size after the pressured of cm ² (D ₅₀₎ mean particle size prior to being this pressure is applied (D ₅₀₎ for coating the 55% on the basis of the figure.

Experimental Example 2

For each of the batteries produced in Examples 1-1 to 9-1 and Comparative Examples 1-1 to 3-1, the charge / discharge current density was 0.1 C, and the end-of-charge voltage was 4.2 V (Li / Li ⁺ ), Two charge and discharge tests with discharge end voltage of 3 V (Li / Li ⁺ ) were performed. Subsequently, the discharge capacity was measured at a charge current density of 0.1 C and a discharge current density of 1 C. 1 C discharge capacity compared to 0.1 C discharge capacity is shown in Table 1 below.

	Anode active material	Loading (mg)	Mixing ratio	Porosity (%)	0.1 C discharge capacity (mAh)	1 C discharge capacity (mAh)	1 C discharge capacity compared to 0.1 C discharge capacity (%)
Example 1-1	Natural Graphite / Titanium Oxide	20.2	50:50	30	5.26	4.73	90
Example 2-1	Natural Graphite / Titanium Oxide	20.2	50:50	25	5.26	4.52	86
Example 3-1	Natural Graphite / Titanium Oxide	20.2	50:50	20	5.26	4.26	81
Example 4-1	Natural Graphite / Titanium Oxide	17.6	70:30	30	5.26	4.47	85
Example 5-1	Natural Graphite / Titanium Oxide	17.6	70:30	25	5.26	4.31	82
Example 6-1	Natural Graphite / Titanium Oxide	17.6	70:30	20	5.26	4.16	79
Example 7-1	Sn / Fe 2 O 3 (1% by weight) coated Sn	5.4	50:50	30	5.26	4.37	83
Example 8-1	Sn / Fe 2 O 3 (5% by weight) coated Sn	5.4	50:50	30	5.26	4.47	85
Example 9-1	Natural Graphite / Artificial Graphite	14.8	50:50	30	5.26	4.26	81
Example 10-1	Natural Graphite / Artificial Graphite	14.8	50:50	25	5.26	4.00	76
Example 11-1	Natural Graphite / Artificial Graphite	14.8	50:50	20	5.26	3.52	67
Comparative Example 1-1	Natural graphite	14.8	-	30	5.26	4.10	78
Comparative Example 2-1	Natural graphite	14.8	-	25	5.26	3.89	74
Comparative Example 3-1	Natural graphite	14.8	-	20	5.26	3.26	62

Referring to Table 1, Examples 1-1, 4-1, 7-1 to 9-1, and Comparative Example 1-1 having the same porosity of the negative electrode active material layer were used together with a relatively high active material. In the case of Examples 1-1, 4-1, and 7-1 to 9-1, it can be seen that they have a larger discharge capacity and a higher 1 C discharge capacity value than the comparative example 1-1.

In addition, when comparing Examples 1-1 to 3-1, Examples 4-1 to 6-1, Examples 9-1 to 11-1 and Comparative Examples 1-1 to 3-1, When the degree of rolling was increased to reduce the porosity of the negative electrode active material layer, Examples 1-1 to 3-1, Example 4-1 to 6-1, and Example 9-1 using relatively high hardness active materials together It can be seen from 11 to 11-1 that the decrease in the value of the 1 C discharge capacity compared to the 0.1 C discharge capacity is smaller than that of Comparative Examples 1-1 to 3-1 using only natural graphite.

Accordingly, when the negative electrode active material layer is formed by mixing the first negative electrode active material having a relatively low hardness and the second negative electrode active material having a relatively high hardness, the second negative electrode active material having a high hardness may properly maintain the size of the pores. As a result, it was confirmed that the secondary battery including the same can exhibit higher discharge capacity and excellent rate characteristics.

Claims (14)

1. A negative electrode active material comprising a mixture of a first negative electrode active material and a second negative electrode active material,

   Hardness of the first negative electrode active material is 1 kg / mm ² to 10 kg / mm ² based on Vicker hardness,

   The second negative electrode active material has a higher hardness than the first negative electrode active material, negative electrode active material.
2. The method of claim 1,

   Hardness of the second negative electrode active material is 11 kg / mm ² based on Vicker hardness To 10,000 kg / mm ² of negative electrode active material.
3. The method of claim 1,

   The first negative electrode active material and the second negative electrode active material will be included in a weight ratio of 99: 1 to 50:50, the negative electrode active material.
4. The method of claim 1,

   The first negative electrode active material may be soft carbon, hard carbon, natural graphite, kish graphite, pyrolytic carbon, liquid phase pitch based carbon fiber, 1 selected from the group consisting of meso-carbon microbeads, mesophase pitches, petroleum or coal tar pitch derived cokes, Al, Zn, Sb, Si, Ge, and Sn The negative electrode active material which is a species or more.
5. The method of claim 1,

   And the second negative electrode active material is at least one selected from the group consisting of artificial graphite, metal carbide, alloys, metal oxides and metals coated with metal oxides.
6. The method of claim 5,

   The metal oxide may be titanium oxide, aluminum oxide, chromium trioxide, zinc oxide, zinc oxide, copper oxide, magnesium oxide, or zirconium dioxide. zirconium dioxide, molybdenum trioxide, vanadium pentoxide, niobium pentoxide, iron oxide, manganese oxide, vanadium oxinde Cobalt oxide (cobalt oxide), nickel oxide (nickel oxide), and tantalum pentoxide (tantalum pentoxide) is at least one selected from the group consisting of, the negative electrode active material.
7. The method of claim 1,

   When the second negative electrode active material is subjected to a pressure of 2,000 kgf / cm ² , the particle size of the direction in which the pressure is applied is 60% or more based on the original particle size.
8. The method of claim 1,

   When the pressure of 2,000 kgf / cm ² is applied to the second negative electrode active material, the particle size in the direction in which the pressure is applied is 80% to 90% based on the original particle size.
9. The method of claim 1,

   Wherein the first cathode active material having an average particle diameter (D ₅₀₎ of 10 nm to 100 ㎛, the negative electrode active material.
10. The method of claim 1,

    The second negative electrode active material has an average particle diameter (D ₅₀ ) of 10 nm to 100 ㎛, negative electrode active material.
11. The method of claim 1,

    The ratio of the particle size of the first negative electrode active material and the second negative electrode active material is 1: 1.1 to 1: 5, the negative electrode active material.
12. A negative electrode comprising a negative electrode active material layer comprising the negative electrode active material according to any one of claims 1 to 11.
13. The method of claim 12,

    The anode active material layer has a porosity of 10 to 60%, the negative electrode.
14. Lithium secondary battery comprising a negative electrode according to claim 12.