KR102256479B1 - Negative electrode active material for lithium secondary battery, and preparing method therof - Google Patents

Abstract

The present invention includes artificial graphite secondary particles in which carbon-based primary particles are assembled, and SiO ₂ nanoparticles are uniformly dispersed and positioned on the surface of the secondary particles, a negative active material for a lithium secondary battery, and lithium containing the same It relates to a secondary battery and a method of manufacturing the same.

Description

Anode active material for lithium secondary battery and its manufacturing method {NEGATIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY, AND PREPARING METHOD THEROF}

The present invention relates to a negative active material for a lithium secondary battery and a method for manufacturing the same, and more particularly, to a negative active material for a lithium secondary battery and a method for manufacturing the same, in which the surface is modified to improve electrode adhesion.

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

Although lithium metal was used as the negative electrode of the conventional secondary battery, the battery short circuit due to the formation of dendrites and the risk of explosion due thereto are known, while maintaining structural and electrical properties, and reversible intercalation of lithium ions. ) And desorbable carbon-based compounds.

The carbon-based compound has a very low discharge potential of about -3 V with respect to the standard hydrogen electrode potential, and excellent electrode life characteristics due to very reversible charging and discharging behavior due to the uniaxial orientation of the graphene layer. Represents. In addition, since the electrode potential is 0V Li/Li+ when charging Li ions, it can exhibit a potential similar to that of pure lithium metal, so that higher energy can be obtained when constructing a battery with an oxide-based positive electrode.

In the negative electrode for a secondary battery using the carbon-based compound, a negative electrode active material slurry is prepared by mixing a conductive material and a binder as necessary with a carbon-based compound as a negative electrode active material, and then the slurry is added to an electrode current collector such as copper foil. It is manufactured by a method of coating and drying, and when the slurry is applied, an active material powder is pressed onto a current collector, and a pressing process is performed to uniformize the thickness of the electrode.

Natural graphite, which is commonly used as a negative electrode, has a large capacity per unit weight, but has a disadvantage in that the degree of orientation is increased during electrode rolling, resulting in deterioration of lithium ions in/out characteristics, thereby deteriorating the rapid charging characteristics of the battery. On the other hand, artificial graphite has an advantage in improving the rapid charging characteristics of a battery because it has a relatively low orientation during electrode rolling than natural graphite, and has good lithium ion input/output characteristics, and also exhibits long life characteristics due to low expansion. There is an advantage.

Although attempts have been made to secure the long-life characteristics of lithium secondary batteries by applying artificial graphite having such advantages, artificial graphite has a disadvantage of low adhesion to the negative electrode current collector, so the development of technology to solve this problem is difficult. Required.

KR 2014-0082036 A

An object to be solved by the present invention is to provide a negative active material for a lithium secondary battery, including artificial graphite secondary particles having an excellent electrode adhesion by modifying the surface.

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

Another object to be solved by the present invention is to provide a method of manufacturing a negative active material for a lithium secondary battery.

In order to solve the above problem,

Including artificial graphite secondary particles in which carbon-based primary particles are granulated,

It provides a negative active material for a lithium secondary battery, in which SiO _{2 nanoparticles having an average particle diameter (D 50} ) of 50 nm to 200 nm are uniformly dispersed and positioned on the surface of the secondary particles.

In addition, the present invention in order to solve the above other problems,

It provides a lithium secondary battery including the negative active material for the lithium secondary battery.

In addition, the present invention in order to solve another problem,

(1) forming secondary particles by mixing the carbon-based primary particles and the adhesive binder;

(2) preparing artificial graphite secondary particles by graphitizing the secondary particles; And

(3) the artificial graphite secondary particles and SiO _{2 Adhering SiO 2} nanoparticles to the surface of the artificial graphite secondary particles by mixing nanoparticles

It provides a method of manufacturing a negative active material for a lithium secondary battery of claim 1 including.

Since the negative electrode active material for lithium secondary battery of the present invention has excellent electrode adhesion by modifying the surface of artificial graphite secondary particles, it has excellent rapid charging characteristics of artificial graphite and long life characteristics due to low expansion, and excellent electrode adhesion according to improved electrode adhesion. Represents the cycle characteristics.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the content of the above-described invention, so the present invention is limited to the matters described in such drawings. It is limited and should not be interpreted.
1 is a view schematically showing a negative active material for a lithium secondary battery according to an example of the present invention.

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

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The negative active material for a lithium secondary battery according to the present invention includes artificial graphite secondary particles in which carbon-based primary particles are granulated, and SiO having _{an average particle diameter (D 50) of 50 nm to 200 nm on the surface of the secondary particles 2} Nanoparticles are uniformly dispersed and positioned.

In the specification of the present invention, the term "primary particle" refers to an original particle when another type of particle is formed from a particle, and a plurality of primary particles are aggregated, bonded, or granulated to form a secondary particle. Can form particles.

In the specification of the present invention, the term "secondary particles (secondary paricles)" refers to large particles that can be physically classified, formed by aggregating, bonding, or granulating individual primary particles.

In the specification of the present invention, the term "assembly" of primary particles refers to a process in which a plurality of primary particles are spontaneously or artificially agglomerated or agglomerated to form an aggregate of primary particles, thereby forming secondary particles. , May be used interchangeably with terms such as set or combination.

The carbon-based primary particles may include, for example, at least one selected from the group consisting of petroleum-based coke, pitch coke, and needle coke.

The primary particles may have an average particle diameter (D ₅₀ ) of 6 μm to 11 μm, and specifically may have an average particle diameter of 8 μm to 10 μm.

In the present invention, the average particle diameter (D ₅₀ ) may be defined as a particle diameter based on 50% of the particle diameter 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 a submicron region, and results having high reproducibility and high resolution can be obtained.

When the average particle diameter (D ₁₀ ) of the primary particles satisfies the range of 6 μm to 11 μm, when they aggregate to form secondary particles, the contact between the primary particles is uniform and the strength of the secondary particles increases. And the secondary particles may appropriately exhibit a particle shape.

The carbon-based primary particles may be mixed with an adhesive binder to form secondary particles.

The adhesive binder may be positioned between the primary input cars to provide an adhesive force between the primary input cars so that they can be aggregated, bonded, or assembled to form secondary particles. Accordingly, the secondary particles may include an adhesive binder between the primary particles. The adhesive binder may include, for example, at least one selected from petroleum-based pitch, coal-based pitch, and mesoface pitch.

The process of forming the secondary particles by mixing the carbon-based primary particles and the adhesive binder may be performed at, for example, 300°C to 900°C, specifically 500°C to 800°C.

When the carbon-based primary particles and the adhesive binder are mixed at 300° C. to 900° C., the volatile components contained in the carbon-based primary particles may be partially removed before the graphitization process by subsequent firing, and the carbon-based Primary particles and adhesive binders can properly form secondary particles

The carbon-based primary particles and secondary particles formed by mixing with the adhesive binder may be graphitized through sintering, and artificial graphite secondary particles may be formed through the graphitization.

The sintering may be performed by heating the secondary particles at a temperature of 2,500°C to 3,500°C, specifically 2,800°C to 3,200°C.

The secondary particle may have a mean particle size (D ₅₀₎ of 13 ㎛ to 23 ㎛, specifically, it may have an average particle diameter (D ₅₀₎ of 16 ㎛ to 21 ㎛.

When the secondary particles have an average particle diameter (D ₅₀ ) of 13 µm to 23 µm, the electrode including it may have a more appropriate electrode density, so that the electrode including it may have an appropriate capacity per volume, and when forming the electrode, the electrode slurry is uniform. It can be suitably coated in thickness.

The SiO ₂ nanoparticles are uniformly dispersed and positioned on the surface of the artificial graphite secondary particles.

The artificial graphite secondary particles decrease the content of functional groups such as -OH that existed on the surface while undergoing a firing process during the manufacturing process, thereby reducing the bonding strength with the negative electrode binder. Therefore, when the negative electrode slurry is formed and coated on the negative electrode current collector, , The adhesion between the secondary artificial graphite particles and the negative electrode current collector and the adhesion between the secondary artificial graphite particles is insufficient. The SiO ₂ nanoparticles are located on the surface of the artificial graphite secondary particles, and improve the reduced bonding strength with the binder according to the reduced functional group content of the artificial graphite secondary particles, thereby improving the problem of low adhesion.

In addition, the SiO ₂ nanoparticles may impart roughness to the surface of the artificial graphite secondary particles to increase adhesion between the negative electrode active material slurry and the electrode current collector during rolling during the negative electrode manufacturing process.

In the context of the present invention, it is that the SiO ₂ nanoparticles being uniformly dispersed in the elimination of the form in which the SiO ₂ nanoparticles are concentrated only on a part area is present in the entire surface of the secondary particles, and the SiO ₂ nanoparticles It is to exclude a form that is located on the surface of the secondary particles aggregated, bonded or aggregated with each other.

1 shows a negative active material for a lithium secondary battery according to an example of the present invention. Referring to FIG. 1, in the negative active material for a lithium secondary battery according to an example of the present invention, it can be seen that the SiO ₂ nanoparticles 200 are dispersed and distributed on the surface of the artificial graphite secondary particles 100.

The SiO ₂ nanoparticles may be located in an area corresponding to 1 area% to 10 area%, specifically 2 area% to 5 area% based on the total surface area of the secondary particles.

When the _{area where the SiO 2} nanoparticles are located is 1 area% to 10 area% based on the total surface area of the secondary particles, the SiO ₂ nanoparticles, which are non-conductors, will exhibit an appropriate adhesion enhancement effect without deteriorating electrical conductivity. I can.

The SiO ₂ nanoparticles do not form a coating layer or shell by covering the entire or most of the surface of the secondary particles, and each SiO ₂ nanoparticle is dispersed and distributed on the surface of the secondary particles. . Accordingly, a portion of the surface of the secondary particle where the SiO ₂ nanoparticles cover the surface of the secondary particle occupies a partial area fraction of the total surface area of the secondary particle.

When the _{amount of the SiO 2} nanoparticles is expressed based on the weight, the negative active material contains the SiO ₂ nanoparticles in 1% to 10% by weight, specifically 1% to 4, more specifically 1% to 2% by weight % Can be included.

When the SiO ₂ nanoparticles are included in the range of 1% by weight to 10% by weight, the capacity per weight of the active material may not be reduced, so that proper cell performance may be maintained, and adhesion of the active material may be improved.

The SiO ₂ nanoparticles may have a particle diameter of 50 nm to 200 nm, and specifically 50 nm to 100 nm.

When the SiO ₂ nanoparticles have a particle diameter of 50 nm to 200 nm, the effect of improving the reduced bonding strength with the binder according to the reduced functional group content of the artificial graphite secondary particles is more excellent, and the artificial graphite secondary particles Appropriate roughness can be given to the surface.

The negative electrode active material for a lithium secondary battery comprises the steps of: (1) forming secondary particles by mixing the carbon-based primary particles and an adhesive binder; (2) preparing artificial graphite secondary particles by graphitizing the secondary particles; And (3) the artificial graphite secondary particles and SiO ₂ It may be prepared by a manufacturing method comprising the step of adhering _{SiO 2} nanoparticles to the surface of the artificial graphite secondary particles by mixing nanoparticles.

(1) forming secondary particles by mixing the carbon-based primary particles and an adhesive binder

In step (1), secondary particles are formed by mixing the carbon-based primary particles and the adhesive binder.

The carbon-based primary particles may include, for example, at least one selected from the group consisting of petroleum-based coke, pitch coke, and needle coke.

The adhesive binder may be positioned between the carbon-based primary particles to provide adhesion between the primary particles so that they can be assembled, bonded, or assembled.

The adhesive binder may include, for example, at least one selected from petroleum-based pitch, coal-based pitch, and mesoface pitch.

The secondary particles may be formed by a conventional method known in the art, for example, by mixing the carbon-based primary particles and an adhesive binder, and blending or kneading. have.

(2) preparing artificial graphite secondary particles by graphitizing the secondary particles

The secondary particles formed through step (1) may be graphitized through sintering.

The sintering may be performed by heating the spherical particles at a temperature of 2,500°C to 3,500°C, specifically 2,800°C to 3,200°C, and the heating is performed for 5 to 20 hours, specifically 10 to 15 hours. I can.

The secondary particles may be graphitized through the graphitization.

(3) the artificial graphite secondary particles and SiO _{2 Adhering SiO 2} nanoparticles to the surface of the artificial graphite secondary particles by mixing nanoparticles

In step (3), the artificial graphite secondary particles prepared through step (2) and SiO _{2 By mixing the nanoparticles and attaching SiO 2} nanoparticles to the surface of the artificial graphite secondary particles, the surface of the artificial graphite secondary particles is modified with _{the SiO 2 nanoparticles.}

The SiO ₂ nanoparticles are 1 wt% to 10 wt%, preferably, 1 wt% to 4 wt%, more preferably 1 wt% to 2 wt%, based on the total weight of the negative active material for a lithium secondary battery to be prepared. It may be mixed with the artificial graphite secondary particles in an amount such that.

The mixing is the artificial graphite secondary particles and SiO ₂ Method of mechanical milling nanoparticles or the artificial graphite secondary particles and SiO ₂ It can be made by a method of mixing and drying the nanoparticles in a solvent.

The mechanical milling includes a roll-mill, a ball-mill, a high energy ball mill, a planetary mill, a stirred ball mill, and a vibrating mill. Alternatively, it may be carried out by mechanically rubbing the artificial graphite secondary particles and the SiO ₂ nanoparticles using a jet-mill, for example, by rotating at a rotation speed of 100 rpm to 1,000 rpm to mechanically compressive stress Can be added. Through the mechanical milling, the SiO ₂ nanoparticles may be attached to the surface of the artificial graphite secondary particles.

Mixing in the solvent includes dispersing and mixing the artificial graphite secondary particles and SiO ₂ nanoparticles in a solvent, and then drying them. After mixing in the solvent, the SiO ₂ nanoparticles are mixed with the artificial graphite through drying. It can be made to adhere to the surface of the secondary particles.

Examples of the solvent include alcohols such as methanol, ethanol, propanol, butanol, heptanol, water, and mixtures thereof, and are not particularly limited as long as they do not affect _{the artificial graphite secondary particles and SiO 2 nanoparticles.} Does not.

Such a negative active material for a lithium secondary battery according to an exemplary embodiment of the present invention can be usefully used as a negative active material for a lithium secondary battery. Accordingly, the present invention provides a lithium secondary battery including the negative active material for a lithium secondary battery.

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

The positive electrode can be manufactured by a conventional method known in the art. For example, after preparing a slurry by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a positive electrode active material, it is applied (coated) to a current collector of a metal material, compressed, and dried to prepare a positive electrode. have.

The current collector of the metallic material is a metal with high conductivity, and is a metal that can be easily adhered to the slurry of the positive electrode active material, and is particularly limited as long as it has high conductivity without causing chemical changes to the battery in the voltage range of the battery. It is not, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like may be used. In addition, it is possible to increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. The current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc., and may have a thickness of 3 to 500 μm.

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 (In the above formula, M ¹ is any one selected from the group consisting of Al, Ga, and In, or two or more of these elements, 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 (in the above formula, 0≤e≤0.2, 0.6≤f≤1, 0≤f'≤0.2, 0≤g≤0.2, and , M ² includes at least one selected from the group consisting of Mn and Ni, Co, Fe, Cr, V, Cu, Zn and Ti, and M ³ is 1 selected from the group consisting of Al, Mg and B A layered compound such as at least one species, and A is at least one 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 , and Cu ₂ V ₂ O _7; Ni site-type lithium nickel oxide represented by the formula LiNi _{1 - i} M ⁴ _i O ₂ (wherein M ⁴ = Co, Mn, Al, Cu, Fe, Mg, B or Ga, 0.01≦i≦0.3); Formula LiMn _{2 - j} M ⁵ _j O ₂ (wherein, M ⁵ = Co, Ni, Fe, Cr, Zn or Ta, 0.01≤j≤0.1) or Li ₂ Mn ₃ M ⁶ O ₈ (in the above formula, M ⁶ = lithium manganese composite oxide represented by Fe, Co, Ni, Cu or Zn); _{LiMn 2} O _{4 in} which part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; LiFe ₃ O ₄ , Fe ₂ (MoO ₄ ) ₃ , and the like, but are not limited thereto.

As a solvent for forming the anode, there are organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide, or water, and these solvents may be used alone or in two or more Can be used by mixing. The amount of the solvent is sufficient as long as it can dissolve and disperse the positive electrode active material, the binder, and the conductive material in consideration of the coating thickness and production yield of the slurry.

As the binder, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), 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, polyacrylic acid and polymers in which hydrogens thereof are substituted with Li, Na or Ca, or Various kinds of binder polymers such as various copolymers may be used.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, Parnes 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 powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. The conductive material may be used in an amount of 1% to 20% by weight based on the total weight of the positive electrode slurry.

The dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The negative electrode may be manufactured by a conventional method known in the art. For example, the negative electrode active material for lithium secondary batteries is used, and additives such as a binder, a conductive material, and a thickener are optionally mixed and stirred to prepare a negative electrode active material slurry. After manufacture, it may be applied to the current collector for a lithium secondary battery, dried, and then compressed.

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

The negative electrode current collector is generally made to have 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 a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, carbon on the surface of copper or stainless steel, Surface treatment with nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

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

As a solvent for forming the negative electrode, there are organic solvents such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide, or water, and these solvents may be used alone or in two or more types. Can be used by mixing. The amount of the solvent is sufficient as long as it can dissolve and disperse the negative electrode active material, the binder, and the conductive material in consideration of the coating thickness and production yield of the slurry.

As the binder, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), 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, polyacrylic acid and polymers in which hydrogens thereof are substituted with Li, Na or Ca, or Various kinds of binder polymers such as various copolymers may be used.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, Parnes 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 powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

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

On the other hand, the separator is a conventional porous polymer film used as a separator in the past, for example, polyolefin such as ethylene homopolymer, propylene homopolymer, ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methacrylate copolymer. A porous polymer film made of a polymer-based polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc., may be used, but is limited thereto. 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 ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^-It may be any one selected from the group consisting of.

Electrolytes used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. that can be used in the manufacture of lithium secondary batteries, and are limited thereto. no.

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

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

Example

Hereinafter, examples and experimental examples will be described in more detail in order to specifically describe the present invention, but the present invention is not limited by these examples and experimental examples. The embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

Example 1

After pulverizing the petroleum needle coke to have an average particle diameter (D ₅₀ ) of 8 µm, it is mixed with petroleum pitch and stirred at a speed of about 40 rpm under a temperature condition of 500°C to 800°C using a blender. By mixing to prepare secondary particles. At this time, volatile components generated from pitch, etc. were exhausted to the outside of the blender. The secondary particles were heat-treated at 3,000° C. in a nitrogen atmosphere to prepare artificial graphite secondary particles having _{an average particle diameter (D 50) of 20 μm.}

A negative active material _{with the SiO 2} nanoparticles attached to the surface of the artificial graphite secondary particles by mechanical milling 98 parts by weight of the prepared artificial graphite secondary particles and _{2 parts by weight of SiO 2 nanoparticles having an average particle diameter (D 50} ) of 100 nm Was prepared.

Example 2

In Example 1, a negative active material was prepared in the same manner as in Example 1, except that the mixing amount of the artificial graphite secondary particles and the SiO _{2 nanoparticles was changed to 95 parts by weight and 5 parts by weight.}

Example 3

In Example 1, a negative active material was prepared in the same manner as in Example 1, except that the mixing amount of the artificial graphite secondary particles and the SiO _{2 nanoparticles was changed to 90 parts by weight and 10 parts by weight.}

Comparative Example 1

The artificial graphite secondary particles having an average particle diameter (D ₅₀ ) of 20 μm prepared in Example 1 were used as a negative electrode active material, and the process of attaching _{the SiO 2} nanoparticles to the surface of the artificial graphite secondary particles was not performed.

Comparative Example 2

A negative electrode in Example 1 as in Example 1, and the same method except that the SiO ₂ particles with a mean particle size (D ₅₀₎ 500 nm in place of the SiO ₂ nano-particles of the average particle diameter (D ₅₀₎ 100 nm An active material was prepared.

Comparative Example 3

Silicon oxide (SiO) having an average particle diameter (D ₅₀ ) of 11.9 μm was pulverized by a ball milling method to prepare a silicon oxide (SiO) having _{an average particle diameter (D 50) of 0.2 μm.}

In Example 1, a negative active material was prepared in the same manner as in Example 1, except that silicon oxide having an average particle diameter (D _{50 ) of 0.2 µm was used instead of the SiO 2 nanoparticles.}

Example 1-1: Preparation of negative electrode

96.5% by weight of the artificial graphite secondary particles prepared in Example 1, 1% by weight of carboxymethyl cellulose (CMC), and 2.5% by weight of styrene butadiene rubber (SBR) were added to NMP and mixed to prepare a negative electrode slurry. The prepared negative active material slurry was coated on one surface of a copper current collector to form an active material layer having a thickness of 65 μm, dried, and then rolled so that the density of the active material layer became 1.6 g/cc, and then punched to a predetermined size. After preparing the negative electrode, it was dried at 130° C. for one day.

Examples 2-1 and 3-1, and Comparative Examples 1-1 to 3-1

Except for using the artificial graphite secondary particles prepared in Examples 2 and 3, and Comparative Examples 1 to 3, respectively, in place of the artificial graphite secondary particles prepared in Example 1 in Example 1-1, A negative electrode was prepared in the same manner as in Example 1-1, and dried.

Experimental Example 1: Evaluation of negative electrode adhesion

Attaching a 4 cm × 2 cm double-sided tape on the slide glass, and cutting the negative electrode prepared in Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1 to a size of 1 cm × 15 cm A constant force was applied with a 2 kg roller to adhere to the double-sided tape. After the slide glass to which the negative electrode was attached was laid at an angle of 180°, the attached negative electrode was peeled off at a speed of 20 m/min, and the force at this time was measured. This was repeated 5 times and the average value is shown in Table 1 below.

Experimental Example 2: Measurement of electrochemical performance

Li metal was used as a counter electrode, and a polyolefin separator was interposed between each of the negative electrodes prepared in Examples 1-1 to 3-1, and Comparative Examples 1-1 to 3-1 and the Li metal. , Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:70 _{by injecting an electrolyte in which 0.5% by weight of vinylene carbonate and 1M LiPF 6} were dissolved, respectively, to prepare a coin-type half-cell. .

For each of the prepared batteries, a charge/discharge test was conducted once with a charge/discharge current density of 0.1 C, a charge end voltage of 4.2 V (Li/Li ⁺ ), and a discharge end voltage of 3 V (Li/Li ^{+ ).} Implemented. Subsequently, the discharge capacity was measured by setting the charge current density to 0.1 C and the discharge current density to 0.5 C. The one-time discharge capacity and initial efficiency were calculated and shown in Table 1 below.

In addition, after charging at the 50th time, the cell was disassembled, washed in DMC, and then the thickness of the electrode was measured, and each negative electrode prepared in Examples 1-1 to 3-1 and Comparative Examples 1-1 to 3-1. By comparing the thickness of and the thickness of the negative electrode in the 50th charged state, the thickness change rate is shown together in Table 1 below.

Adhesion (gf/cm) 1 time
Discharge capacity Initial efficiency Thickness increase rate (%)
<Thickness of negative electrode 50 times/thickness of initial negative electrode> Example 1-1 46.3 361.1 93.3 25 Example 2-1 52.5 355.2 90.6 30 Example 3-1 58.9 349.7 86.2 27 Comparative Example 1-1 16.3 361.5 93.6 Not measurable by cathodic detachment Comparative Example 2-1 23.5 360.3 93.4 28
(Part of the negative electrode edge is removed) Comparative Example 3-1 44.3 380.8 92.6 47

Referring to Table 1, in the case of the negative electrode according to Examples 1-1 to 3-1, adhesion is superior compared to Comparative Examples 1-1 to 3-1, and when manufacturing a secondary battery using this, even after charging 50 times. It was confirmed that the negative electrode (negative electrode active material layer) exhibited an excellent thickness increase rate without causing detachment.

_{On the other hand, the negative electrode of Comparative Example 1-1 prepared using the negative electrode active material in which the SiO 2} nanoparticles were not located on the surface of the artificial graphite secondary particles had poor adhesion, and when a secondary battery was manufactured using this, after 50 cycles. In the negative electrode, desorption occurred.

In addition, the negative electrode of Comparative Example 2-1 prepared using a negative active material having an excessively large average particle diameter of _{the SiO 2} particles located on the surface of the artificial graphite secondary particles exhibited improved adhesion to some extent compared to Comparative Example 1-1. However, compared to Examples 1-1 to 3-1, the degree of improvement was insufficient, and when a secondary battery was manufactured using this, after 50 cycles, detachment occurred at the edge of the negative electrode.

On the other hand, the negative electrode of Comparative Example 3-1 prepared using the negative electrode active material in which SiO is located on the surface of the artificial graphite secondary particles showed improved adhesion compared to Comparative Examples 1-1 and 2-1, but using this When the secondary battery was manufactured, it was confirmed that after 50 cycles, the thickness of the negative electrode increased significantly, resulting in a swelling problem of the negative electrode.

100: artificial graphite secondary particles
200: SiO ₂ nanoparticles

Claims (12)

Including artificial graphite secondary particles in which carbon-based primary particles are granulated,
SiO _{2 nanoparticles having an average particle diameter (D 50} ) of 50 nm to 200 nm on the surface of the secondary particles are uniformly dispersed and located, a negative active material for a lithium secondary battery.
The method of claim 1,
The carbon-based primary particles include at least one selected from the group consisting of petroleum-based coke, pitch coke, and needle coke.
The method of claim 1,
The primary particles have an average particle diameter (D ₅₀ ) of 6 μm to 11 μm, a negative active material for a lithium secondary battery.
The method of claim 1,
The secondary particles include an adhesive binder positioned between the primary particles, a negative active material for a lithium secondary battery.
The method of claim 4
The adhesive binder comprises at least one selected from the group consisting of petroleum-based pitch, coal-based pitch, and meso-face pitch, a negative active material for a lithium secondary battery.
The method of claim 1,
The secondary particles have an average particle diameter (D ₅₀ ) of 13 μm to 23 μm, a negative active material for a lithium secondary battery.
The method of claim 1,
The SiO ₂ nanoparticles are located only on a part of the surface of the secondary particles, a negative active material for a lithium secondary battery.
The method of claim 7,
A portion _{of the surface of the secondary particles on which the SiO 2} nanoparticles are located is 5 area% to 50 area% based on the total surface area of the secondary particles, a negative active material for a lithium secondary battery.
The method of claim 1,
The negative active material comprises _{1% to 4% by weight of the SiO 2} nanoparticles, a negative active material for a lithium secondary battery.
A lithium secondary battery comprising the negative active material for a lithium secondary battery according to any one of claims 1 to 9.
(1) forming secondary particles by mixing the carbon-based primary particles and the adhesive binder;
(2) preparing artificial graphite secondary particles by graphitizing the secondary particles; And
(3) the artificial graphite secondary particles and SiO _{2 Adhering SiO 2} nanoparticles to the surface of the artificial graphite secondary particles by mixing nanoparticles
A method for producing a negative active material for a lithium secondary battery of claim 1 comprising a.
The method of claim 11,
The mixing of step (3) is performed _{by a method of mechanically milling the artificial graphite secondary particles and SiO 2} nanoparticles or mixing and drying them in a solvent, a method of preparing a negative active material for a lithium secondary battery.

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