KR102273647B1 - Positive electrode for rechargeable lithium battery and rechargeable lithium battery including the same - Google Patents

Abstract

A positive electrode for a lithium secondary battery comprising a composite positive electrode active material in which a first conductive material is complexed on a surface of a positive electrode active material capable of reversibly intercalating and releasing lithium, a second conductive material, and a binder having a tensile modulus of 900 MPa or less, and a lithium secondary including the same A battery is provided.

Description

A positive electrode for a lithium secondary battery and a lithium secondary battery including the same

A positive electrode for a lithium secondary battery and a lithium secondary battery including the same.

In recent years, with the miniaturization of information processing devices such as mobile phones and notebook computers, improvement of battery characteristics of lithium secondary batteries that can be used as power sources for these information processing devices has been demanded.

For example, Japanese Patent Application Laid-Open No. 2012-146590 proposes a technique for improving the capacity of a lithium secondary battery by increasing the density of the positive electrode. Specifically, it is suggested to adjust the average particle diameter of the positive electrode active material and the conductive material to enable the closest filling in order to increase the density of the positive electrode mixture layer.

However, in this case, since the slidability on the surface of the positive electrode active material is not sufficient, the state of charge of the positive electrode is not good and the densification of the positive electrode is insufficient.

One embodiment is to provide a positive electrode for a lithium secondary battery capable of high density.

Another embodiment is to provide a lithium secondary battery including the positive electrode for the lithium secondary battery.

One embodiment is a composite positive electrode active material in which a first conductive material is complexed on the surface of a positive electrode active material capable of reversibly occluding and releasing lithium; a second conductive material; And it provides a positive electrode for a lithium secondary battery comprising a binder having a tensile modulus of 900 MPa or less.

The first conductive material may include flaky graphite, graphene, or a combination thereof.

An average particle diameter (D50) of the first conductive material may be 0.5 μm to 3 μm.

The first conductive material may be composited in an amount of 0.3 wt% to 1 wt% based on the total amount of the composite cathode active material.

The total amount of the first conductive material and the second conductive material may be 0.6 wt% to 2.0 wt% based on the total amount of the composite positive electrode active material, the second conductive material, and the binder.

The positive active material capable of reversibly intercalating and releasing lithium may include a lithium transition metal oxide.

The binder may include a copolymer formed by polymerization of two or more different monomers, specifically, the binder is vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-chlorotrifluoro ethylene copolymers, mixtures of polyvinylidenefluoride and hydrogenated acrylonitrile-butadiene copolymers, or combinations thereof.

Another embodiment provides a lithium secondary battery including the positive electrode.

The details of other implementations are included in the detailed description below.

By providing a high-density positive electrode, a high-capacity lithium secondary battery can be realized.

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

Unless otherwise specified in the specification, when a part such as a layer, film, region, plate, etc. is "on" another part, it is not only when it is "on" another part, but also when there is another part in between. include

Hereinafter, a lithium secondary battery according to an embodiment will be described with reference to FIG. 1 .

1 is a cross-sectional view showing a schematic configuration of a lithium secondary battery according to an embodiment.

Referring to FIG. 1 , the lithium secondary battery 10 includes a positive electrode 20 , a negative electrode 30 , a separator 40 , and a non-aqueous electrolyte. The shape of the lithium secondary battery 10 is not particularly limited, and may be, for example, a cylindrical shape, a prismatic shape, a laminate type, a button type, or the like.

The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22 .

The current collector 21 may include, but is not limited to, aluminum.

The positive electrode active material layer 22 may include a composite positive electrode active material in which a first conductive material is complexed on a surface of a positive electrode active material capable of reversibly occluding and releasing lithium, a second conductive material, and a binder.

The positive active material is a material capable of reversibly occluding and releasing lithium, and may include a lithium transition metal oxide. A lithium secondary battery using the lithium transition metal oxide as a positive electrode active material may have a high potential and a high capacity.

Examples of the lithium transition metal oxide include lithium cobalt composite oxide such as _{LiCoO 2} , lithium nickel cobalt manganese composite oxide such as _{LiNi x} Co _y Mn _z O _{2 , LiNiO 2} and lithium nickel-based composite oxides, _{such as lithium manganese composite oxides, such as LiMn 2} O ₄ , and these may be used alone or in combination of two or more thereof.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited. In addition, in order to suppress a side reaction with the electrolyte solution at the time of high voltage, the said positive electrode active material may use the thing which surface-treated said each material.

The average agglomerated particle diameter of the positive active material may be 10 μm to 30 μm. When the particle size is within the above range, safety or filling properties of the positive active material may be improved. The average agglomerated particle diameter represents a 50% integration value (D50 value) of the diameter distribution when secondary particles formed by agglomeration of primary particles of a material capable of reversibly occluding and releasing lithium are considered as spheres. It can measure by the diffraction/scattering method.

When a material in which the first conductive material is complexed on the surface of the positive electrode active material is used for the positive electrode, it is possible to increase density of the positive electrode. In addition, by compounding the first conductive material on the surface of the positive electrode active material, higher conductivity can be obtained compared to a case where the same amount of the conductive material and the positive electrode active material are simply mixed. In general, a conductive material is added to secure the conductivity of the positive electrode, but when a large amount is added, the filling property of the positive electrode active material is reduced due to high steric hindrance and increased slip resistance. However, according to one embodiment, since the amount of the second conductive material can be suppressed, steric hindrance and sliding resistance caused by the conductive material can be reduced, and the filling properties and bulk density of the positive electrode can be improved.

Here, the compounding refers to coating the first conductive material by firmly bonding the first conductive material to the surface of the positive electrode active material. The complexing may be performed, for example, by a dry mechanochemical method, an electro-fluid coating method by wet spraying, a spray coat method, a forced deposition method, or the like.

The dry mechanochemical method is, for example, a method of uniformly imparting impact force, shear force, and compressive force to each of the particles of the mixed powder of the raw material. Complexing by the dry mechanochemical method can be performed, for example, by Nobilta manufactured by Hosokawa Micron, or the like.

The first conductive material may be a carbon-based material, and specifically, may include flaky graphite, graphene, or a combination thereof, and these may be flaky. By compounding the first conductive material of the above type on the surface of the positive electrode active material, the slidability of the positive electrode active material can be improved. Accordingly, it is possible to improve the filling properties during the production of the positive electrode, and to increase the density of the positive electrode. In addition, since the first conductive material can efficiently impart conductivity to the composite positive electrode active material by the composite, the amount of the second conductive material can be suppressed. For this reason, the steric hindrance and sliding resistance caused by the second conductive material are reduced, so that the anode can be more dense.

For example, the first conductive material may be added in an amount of 0.3 wt % to 1 wt % based on the total amount of the composite positive active material to be compounded, and specifically may be added in an amount of 0.6 wt % to 1 wt %. When the amount of the first conductive material is within the above range, the first conductive material may improve the sliding property of the positive electrode active material without inhibiting the movement of lithium ions in order to properly coat the surface of the positive electrode active material. Accordingly, the positive electrode for a lithium secondary battery according to an embodiment may improve bulk density while maintaining battery characteristics.

The average particle diameter (D50) of the first conductive material may be 0.5 μm to 3 μm, for example, 1 μm to 3 μm. When the D50 of the first conductive material is within the above range, the slidability of the first conductive material may be improved, so that the bulk density of the positive electrode active material layer may be increased. In this case, the average particle diameter D50 means a particle diameter at which the integrated value becomes 50% in the particle size distribution of the diameter when the particles of the first conductive material are regarded as spheres. In addition, the average particle diameter (D50) of the first conductive material may be measured, for example, by a laser diffraction/scattering method.

The second conductive material may be, for example, a carbon-based material such as carbon black such as ketjen black or acetylene black, carbon nanotubes, natural graphite, or artificial graphite, but is not limited thereto. .

The second conductive material may impart conductivity to the positive active material layer 22 . The second conductive material is not compounded with the positive electrode active material, and when included in the positive electrode active material layer 22 , the positive electrode active material layer 22 may further obtain conductivity.

The total addition amount of the first conductive material and the second conductive material is 0.6 wt % to 2.0 with respect to the total amount of the positive electrode active material layer 22 , that is, based on the total amount of the composite positive electrode active material, the second conductive material, and the binder. It may be weight %, for example, it may be 0.8 weight % to 1.5 weight %. When the total addition amount of the first and second conductive materials is within the above range, sufficient conductivity can be provided, and the positive electrode has excellent compression moldability and fillability, thereby realizing high density of the positive electrode.

The binder may bind the composite positive electrode active material and the second conductive material on the current collector 21 .

The binder may have a tensile modulus of 900 MPa or less, for example, 300 MPa to 900 MPa. When the tensile modulus of elasticity of the binder is within the above range, it is possible to improve the compression moldability when manufacturing the positive electrode due to high flexibility, thereby improving the bulk density of the positive electrode active material layer and increasing the density of the positive electrode. The tensile modulus can be measured, for example, by a tensile test of ASTM D638.

The binder may include at least one copolymer. In this case, the copolymer is a polymer formed by polymerization of two or more different monomers, and may be distinguished from a homopolymer formed by polymerization of a single monomer. When the copolymer is used, a binder having a tensile modulus of 900 MPa or less can be obtained.

The binder may be, for example, a vinylidenefluoride-tetrafluoroethylene copolymer, a vinylidenefluoride-chlorotrifluoroethylene copolymer, a mixture of polyvinylidenefluoride and a hydrogenated acrylonitrile-butadiene copolymer, or combinations thereof may be included. Among them, vinylidenefluoride-tetrafluoroethylene copolymer can be used. The binder is difficult to swell by an electrolyte solution or the like and has excellent oxidation resistance. The vinylidene fluoride-tetrafluoroethylene copolymer can control the tensile modulus of elasticity of the binder by controlling the polymerization ratio of vinylidene fluoride and tetrafluoroethylene. Specifically, as the polymerization ratio of tetrafluoroethylene increases, The tensile modulus may be lowered.

The content of the binder in the positive electrode active material layer 22 is not particularly limited, and any range is possible as long as the content is applied to the positive electrode active material layer of a conventional lithium secondary battery.

The positive electrode active material layer 22 includes, for example, a composite positive electrode active material in which the first conductive material is complexed on the surface of the positive electrode active material in an organic solvent such as N-methyl-2-pyrrolidone, the second conductive material and The slurry in which the binder is dispersed may be coated on the current collector 21 , and may be formed by drying and rolling. The coating method includes, for example, a doctor blade method, a slot die method, a knife coater method, and a gravure coater method. The thickness in particular of the formed positive electrode active material layer 22 is not restrict|limited, What is necessary is just the thickness which the positive electrode active material layer of a lithium secondary battery has.

The negative electrode 30 includes a current collector 31 and an anode active material layer 32 .

The current collector 31 may include, for example, copper (Cu), nickel (Ni), or the like.

The negative electrode active material layer 32 may be any type as long as it is used as a negative electrode active material layer of a lithium secondary battery. For example, the anode active material layer 32 may include an anode active material and may further include a binder.

As the anode active material, a carbon-based material, a silicon-based material, a tin-based material, lithium metal oxide, metallic lithium, etc. may be used alone or in combination of two or more. The carbon-based material may be, for example, artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, or a graphite-based material such as natural graphite coated with artificial graphite. The silicon-based material may be, for example, silicon, silicon oxide, a silicon-containing alloy, or a mixture of these and a graphite-based material. The silicon oxide may be expressed as SiOx (0.5≤x≤1.5). The silicon-containing alloy is an alloy in which the content of silicon is the highest among all metal elements with respect to the total amount of the alloy, and for example, a Si-Al-Fe alloy may be mentioned. The tin-based material may be, for example, tin, tin oxide, a tin-containing alloy, or a mixture of these and a graphite-based material. The lithium metal oxide may include, for example, a titanium oxide-based compound such as _{Li 4} Ti ₅ O _{12 .}

The binder is not particularly limited, and the same binder as the binder used in the positive electrode may be used.

The weight ratio of the negative active material and the binder is not particularly limited, and a weight ratio used in a conventional lithium secondary battery may be used.

The negative electrode 30 may be manufactured as follows. A mixture of the negative active material and the binder in a desired ratio is dispersed in a solvent such as water to prepare a slurry, then the slurry is applied on the current collector 31, dried and rolled to form the negative active material layer 32 can form. At this time, the thickness of the negative active material layer 32 is not particularly limited, and may be any thickness that the negative active material layer of the lithium secondary battery has. In addition, when metallic lithium is used as the anode active material layer 32 , a metallic lithium foil may be overlapped on the current collector 31 .

The separator layer 40 may include a separator and an electrolyte.

The separator in particular is not restrict|limited, As long as it is used as a separator of a lithium secondary battery, what kind may be sufficient. For example, a porous membrane or a nonwoven fabric exhibiting excellent high rate discharge performance may be used alone or in combination.

In addition, the separator Al ₂ O ₃ , Mg(OH) ₂ , SiO _{2 A} surface coated with an inorganic material such as SiO 2 may be used.

As the material of the separator, for example, polyolefin resin, polyester resin, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidenefluoride-ethylene copolymer, vinylidenefluoride-propylene copolymer, vinylidenefluoride-trifluoropropylene copolymer, vinylidenefluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride Ride-ethylene-tetrafluoroethylene copolymer etc. are mentioned. Examples of the polyolefin-based resin include polyethylene and polypropylene, and examples of the polyester-based resin include polyethylene terephthalate and polybutylene terephthalate.

The porosity of the separator is not particularly limited, and the porosity of the separator of the lithium secondary battery may be arbitrarily applied.

The electrolyte may have a composition in which an electrolyte salt is contained in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate, and methyl butyric acid; tetrahydrofuran or a derivative thereof; ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, and methyl diglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or a derivative thereof; Ethylene sulfide, sulfolane, sultone or a derivative thereof may be used alone or as a mixture of two or more, but is not limited thereto.

The electrolyte salt is, for example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiPF _{6 -x} (CnF _{2n +1} ) _x (1<x<6, n=1 or 2), LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , an inorganic ion salt containing one of lithium, sodium, or potassium such as KSCN; LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ ), LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H _{7 )} ) ₄ NBr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C _{2 )} and organic ionic salts such as H ₅ ) ₄ N-phthalate, lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzenesulfonate, and these ionic compounds may be used alone or in combination of two or more.

The concentration of the electrolyte salt is not particularly limited, and may be used, for example, in a concentration of 0.5 to 2.0 mol/L.

Hereinafter, the manufacturing method of the lithium secondary battery 10 is demonstrated.

The above-described separator is disposed between the positive electrode 20 and the negative electrode 30 to prepare an electrode structure, and then the electrode structure is processed into a desired shape, such as a cylindrical shape, a square shape, a laminate type, a button type, etc., and the corresponding shape inserted into the container of Then, by injecting the non-aqueous electrolyte into the container and impregnating the pores in the separator with the electrolyte, a lithium secondary battery can be manufactured.

Hereinafter, specific embodiments of the present invention are presented. However, the examples described below are only for specifically illustrating or explaining the present invention, and the present invention is not limited thereto. In addition, since the content not described here can be sufficiently technically inferred by a person skilled in the art, the description thereof will be omitted.

Example One

(anode manufacturing)

A composite positive electrode active material was prepared _{by adding flaky graphite, which is a first conductive material, to LiCoO 2} as a positive electrode active material, and then dry-compositing by Nobilta Nob-mini (manufactured by Hosokawa Micron). At this time, 0.6 wt% of the first conductive material was added based on the total amount of the composite positive active material, and the composite was performed for 5 minutes with a load power of 500W. In addition, the average particle diameter (D50) of the first conductive material was 3 μm as measured by a laser diffraction/scattering particle size analyzer MT3000 (Microtrack).

Next, the prepared composite positive electrode active material, carbon black as a second conductive material, and a vinylidene fluoride-tetrafluoroethylene (VdF-TFE) copolymer having a tensile modulus of 700 MPa were mixed, and N-methyl pyrrolidone (NMP) A slurry was prepared by adding an appropriate amount of the solution, mixing and dispersing. The tensile modulus of elasticity of the VdF-TFE copolymer was measured by a universal testing machine Autograph AGS-X (manufactured by SHIMADZU) according to ASTM D638. In addition, the amount of carbon black added was determined so that the total amount of the first conductive material and the second conductive material was 1.2% by weight based on the total amount of the positive electrode active material layer mixture. In addition, the binder was added in an amount of 1.2 wt% based on the total amount of the positive electrode active material layer mixture.

Then, the prepared slurry was coated on an aluminum foil having a thickness of 12 μm as a current collector so that the areal density of the mixture solid was 25 mg/cm ² , and dried to prepare a positive electrode.

In addition, in the same manner as in Example 1, positive electrodes for secondary batteries according to Examples 2 to 9 and Comparative Examples 1 to 10 were produced. Here, in Examples 2 to 9 and Comparative Examples 1 to 10, the type, average particle size and addition amount of the first conductive material, the type of the second conductive material, the total amount of the conductive material added, and the binder were combined with respect to Example 1 It was produced by changing the type and tensile modulus of elasticity, respectively.

(Cathode Manufacturing)

A slurry was prepared by mixing and dispersing graphite as an anode active material, styrene-butadiene rubber (SBR) as a binder, and an aqueous solution of carboxymethyl cellulose (CMC) as a thickener in a weight ratio of 98:1:1 with water. The slurry was applied on a copper foil having a thickness of 6 μm as a current collector, dried and rolled to prepare a negative electrode.

(Lithium secondary battery production)

The prepared positive and negative electrodes were cut into predetermined sizes, and a current collector tab with a sealant was welded to a metal foil serving as a current collector. Next, a separator made of a polyolefin microporous film ND314 (manufactured by ASAHI KASEI E-MATERIALS) was disposed between the positive electrode and the negative electrode to prepare an electrode structure. The electrode structure was inserted into a laminate container composed of a laminate of polyethylene terephthalate and aluminum, and the current collecting tab was protruded from the opening to the outside, and then the laminate exterior body was heat sealed in the sealant part of the current collecting tab. .

_{LiPF 6} was dissolved to a concentration of 1.3 mol/L in a solvent mixed with ethylene carbonate (EC) and ethylmethyl carbonate (EMC) in a volume ratio of 3:7 _{to LiPF 6} A solution was prepared. Then, an electrolyte solution was prepared by mixing 10 parts by weight of fluoroethylene carbonate with respect to 90 parts by weight of _{the LiPF 6 solution.}

The prepared electrolyte solution was injected into the opening of the laminate exterior body into which the electrode structure was inserted, and then the opening of the exterior body was sealed under reduced pressure, thereby manufacturing a lithium secondary battery.

Example 2 to 9 and comparative example 1 to 5

Except for the difference in the type of the first conductive material, the average particle diameter (D50) of the first conductive material, the amount of addition of the first conductive material, the type of the second conductive material, the total amount of the first and second conductive materials, the type of binder and the tensile modulus of elasticity, etc. produced a lithium secondary battery in the same manner as in Example 1.

Evaluation 1: Anode of the active material layer bulk density

In the positive electrodes prepared in Examples 1 to 9 and Comparative Examples 1 to 5, the bulk density of the positive electrode active material layer was measured, and the results are shown in Table 1 below.

Specifically, the thickness of the positive electrode active material layer and the weight per unit area when pressed with a roll press machine under a load of 5 t were measured, and the bulk density was calculated.

Evaluation 2: Cycle Life Characteristics

The lithium secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 5 were charged and discharged under the following conditions to measure cycle life, and the results are shown in Table 1 below.

1 cycle: CC-CV charging (constant current constant voltage charging) is performed at 0.1C until the voltage becomes 4.4V, and CC discharge (constant current discharge) is performed at 0.1C until the voltage is 2.75V

2 cycles: CC-CV charging at 0.2C until voltage is 4.4V, CC discharging at 0.2C until voltage is 2.75V

After 3 cycles: CC-CV charging at 1.0C until the voltage is 4.4V, performing constant current discharge at 1.0C until the voltage is 2.75V, repeat

In Table 1 below, the capacity retention ratio (%) is calculated as a percentage of the discharge capacity at 300 cycles compared to the discharge capacity at 3 cycles.

Composite cathode active material Second conductive material type Total content of first + second conductive material (wt%) bookbinder Bulk density of the positive electrode active material layer (g/cm ³ ) Volume
Retention (%) First conductive material type First conductive material D50 (㎛) First conductive material content (wt%) Kinds Tensile modulus (MPa) Example 1 flaky graphite 3 0.6 CB 1.2 VdF-TFE copolymer 1 700 4.16 86 Example 2 flaky graphite 1.5 0.3 CB 1.2 VdF-TFE copolymer 1 700 4.16 87 Example 3 flaky graphite 1.5 0.6 CB 1.2 VdF-TFE copolymer 1 700 4.19 87 Example 4 flaky graphite 1.5 One CB 1.2 VdF-TFE copolymer 1 700 4.21 81 Example 5 graphene 0.7 0.6 CB 1.2 VdF-TFE copolymer 1 700 4.20 89 Example 6 flaky graphite 1.5 0.6 CB 1.2 VdF-TFE copolymer 2 900 4.17 86 Example 7 flaky graphite 1.5 0.6 CB 1.2 VdF-TFE copolymer 3 500 4.21 88 Example 8 flaky graphite 1.5 0.6 CB 1.2 PVdF + H-NBR 700 4.19 85 Example 9 flaky graphite 1.5 0.6 CB 1.2 VdF-TFE copolymer 700 4.19 81 Comparative Example 1 - - - CB 1.2 PVdF 1100 4.05 84 Comparative Example 2 - - - CB 1.2 VdF-TFE copolymer 1 700 4.08 85 Comparative Example 3 - - - CB+Flake Graphite (1:1) 1.2 VdF-TFE copolymer 1 700 4.10 86 Comparative Example 4 - - - flaky graphite 1.2 VdF-TFE copolymer 1 700 4.12 20 Comparative Example 5 flaky graphite 1.5 0.6 CB 1.2 PVdF 1100 4.14 86

- The content of the first conductive material is for the total amount of the composite positive active material

- CB is carbon black

- The total content of the first + second conductive material relates to the total amount of the positive electrode active material layer, that is, the total amount of the composite positive electrode active material, the second conductive material, and the binder

- VdF-TFE copolymer is vinylidene fluoride-tetrafluoroethylene copolymer

- VdF-TFE copolymers 1 to 3 change the polymerization ratio of vinylidene fluoride and tetrafluoroethylene, and the polymerization ratio of tetrafluoroethylene increases from 1 to 3

- PVdF + H-NBR is a mixture of polyvinylidene fluoride and hydrogenated acrylonitrile-butadiene copolymer

Referring to Table 1, in the case of Examples 1 to 9 comprising a positive electrode active material in which a first conductive material is composited on the surface of the positive electrode active material, a second conductive material, and a binder having a tensile modulus of 900 MPa or less, the non-composite positive active material It can be seen that the bulk density of the positive electrode active material layer is improved without deterioration of cycle life characteristics compared to Comparative Examples 1 to 5 using a binder or a binder having a tensile modulus of greater than 900 MPa. Accordingly, it can be seen that a high-capacity lithium secondary battery can be realized as the positive electrode according to an embodiment can be high-densified while maintaining excellent battery performance.

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It belongs to the scope of the invention.

10: lithium secondary battery
20: positive electrode
21: current collector
22: positive electrode active material layer
30: cathode
31: current collector
32: anode active material layer
40: separator layer

Claims (9)

a composite positive electrode active material in which a first conductive material is complexed on the surface of a positive electrode active material capable of reversibly intercalating and releasing lithium;
a second conductive material; and
A binder having a tensile modulus of 900 MPa or less
including,
The first conductive material includes flaky graphite, graphene, or a combination thereof,
The average particle diameter (D50) of the first conductive material is 0.5 μm to 3 μm,
The total amount of the first conductive material and the second conductive material is 0.6 wt % to 2.0 wt % based on the total amount of the composite positive electrode active material, the second conductive material, and the binder. delete delete According to claim 1,
The first conductive material is a cathode for a lithium secondary battery that is composited in an amount of 0.3 wt% to 1 wt% based on the total amount of the composite cathode active material. delete According to claim 1,
The positive electrode active material capable of reversibly intercalating and releasing lithium is a positive electrode for a lithium secondary battery comprising a lithium transition metal oxide. According to claim 1,
The binder is a positive electrode for a lithium secondary battery comprising a copolymer (copolymer) formed by polymerization of two or more different monomers. According to claim 1,
The binder is a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-chlorotrifluoroethylene copolymer, a mixture of polyvinylidene fluoride and hydrogenated acrylonitrile-butadiene copolymer, or a combination thereof A positive electrode for a lithium secondary battery comprising. A lithium secondary battery comprising the positive electrode of any one of claims 1, 4, and 6 to 8.

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