KR20060071385A - Anode active material for lithium secondary battery having high energy density - Google Patents

Abstract

The present invention relates to a negative active material for a lithium secondary battery, comprising a single structure powder having no coating layer and a core / shell structure powder having a coating layer 1: 0.1 to 10 weight ratio, and having a negative electrode mixture density of 1.90 g / cc or less and 8% or less Characterized in that having a spring-back (spring-back) characteristics of the lithium secondary battery comprising a negative electrode prepared from the negative electrode active material composition comprising a negative electrode active material of the present invention has a high energy density, excellent battery capacity and life characteristics Indicates.

Description

Anode active material for high energy density lithium secondary battery {ANODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY HAVING HIGH ENERGY DENSITY}

The present invention relates to a negative electrode active material that can be used in the manufacture of a high energy density lithium secondary battery.

A lithium secondary battery generally has a structure including a negative electrode, a positive electrode, an electrolyte, and a lithium ion-permeable separator between the electrodes. The negative electrode of the lithium secondary battery may include a negative electrode active material (eg, carbon-based material), a conductive agent (eg, carbon black), a binder (eg, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR)), and a solvent (eg, : N-methylpyrrolidone (NMP), water) is prepared by coating the surface of the current collector in the form of a slurry in the form of a slurry, drying and pressing.

As the negative electrode active material, crystalline carbon and amorphous carbon have been mainly used. When the negative electrode is manufactured from a negative electrode composition including a single negative electrode active material, there is a limit in improving the packing density and increasing the capacity of the negative electrode plate. Techniques for mixing two or more different negative electrode active materials or coating or surface treating a surface of a negative electrode active material have been proposed.

For example, U. S. Patent No. 5,273, 842 discloses a technique of classifying the particle size distribution of the negative electrode active material to be a grading distribution and applying the same to the manufacturing of the negative electrode. However, this method has the disadvantage that the consumption of the negative electrode active material is high and the manufacturing time of the negative electrode active material itself is long.

In addition, Korean Patent Publication Nos. 1999-80594 and 2002-57347 disclose a method of manufacturing a negative electrode active material having a core / shell structure, that is, a multilayer structure by coating the surface of crystalline carbon with amorphous carbon by wet and dry methods, respectively. Is starting. The thus prepared multilayer active material has a small expandability during intercalation and desorption of lithium and hardly causes irreversible reaction at the interface between the powder and the electrolyte. Has the disadvantage.

Furthermore, Korean Patent Laid-Open Publication No. 1999-30823 discloses using a mixture of graphite carbon fibers and graphite carbon particles as a negative electrode active material, but in this case, the powder filling property between the carbon fibers and the carbon particles There is still a limit in improving the filling density of the negative electrode apart, there is a problem that the membrane is damaged due to the exposure of carbon fiber to the negative electrode surface.

Accordingly, an object of the present invention is to include a negative electrode active material capable of maximizing the packing density of the negative electrode and minimizing the deformation of the negative electrode during intercalation and desorption of lithium, and a negative electrode prepared from a negative electrode active material composition comprising the same. It is to provide a lithium secondary battery having energy density, excellent battery capacity and lifespan characteristics.

In order to achieve the above object, in the present invention, a single structure powder having no coating layer and a core / shell structure powder having a coating layer 1: 0.1 to 10 weight ratio, and a spring mixture of 8% or less at a negative electrode mixture density of 1.90 g / cc or less Provided is a negative electrode active material for a lithium secondary battery having a spring property.

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

The negative electrode active material for a lithium secondary battery according to the present invention is characterized in that it comprises a combination of 1: 0.1 to 10 weight ratio of uncoated single structure powder and coated core / shell structure (multilayer structure) powder.

In the present invention, the single-structure powder usable as the negative electrode active material is selected from the group consisting of crystalline carbon (eg, natural graphite, artificial graphite, etc.), amorphous carbon, metals, alloys, metal oxides, metal nitrides, fluorine, and mixtures thereof. It is preferable that this single structure powder has an average volume particle size in the range of 0.01 to 40 μm.

In addition, the coated core / shell structure powder usable as the negative electrode active material in the present invention is crystalline carbon (eg, natural graphite, artificial graphite, etc.), amorphous carbon, metals, alloys, metal oxides, metal nitrides, fluorine and these It may consist of a core and a shell component each differently selected from the group consisting of a mixture of crystalline carbon, metals, alloys, metal oxides and metal nitrides having an amorphous or crystalline carbon coating layer; And crystalline carbon and amorphous carbon having at least one selected from a metal, an alloy, a metal oxide, and fluorine as a coating layer. Preferably, the core of this core / shell structure powder has an average volume particle size in the range of 0.01 to 40 μm, and the shell may have a thickness in the range of 0.001 to 1 μm.

The core / shell structure powder may be prepared by coating a single structure of the powder (core component) surface with a heterogeneous powder (shell component) by a conventional wet method or a dry method, specifically, a precursor of the core component in an organic solvent. After the shell component is mixed and refluxed, it is filtered and heat treated (wet method, see Korean Patent Laid-Open Publication No. 1999-80594), or the powder core component and the powder shell component are physically generated to generate heat, and then 500 to 2800. The coating may be performed by heat treatment in two steps at 1 ° C. for 1 to 6 hours (dry method, see Korean Patent Publication No. 2002-57347).

The powder of single structure has the advantage that it is expandable during intercalation and desorption of lithium and causes a lot of irreversible reactions at the interface between powder and electrolyte, whereas it has high filling property when rolling electrode, which can increase the mixture density and electrical conductivity. In contrast to the physical properties of the powder of a single structure, the core / shell structure powder has a small expandability and little irreversible reaction during intercalation and desorption of lithium, whereas the packing density and electrical properties are low when the electrode is rolled. It is disadvantageous in terms of conductivity. According to the present invention, the uncoated negative electrode active material powder having a single structure and the negative electrode active material powder having a core / shell structure can be mixed in a ratio of 1: 0.1 to 10 by weight to highlight the advantages of each powder and to compensate for the respective disadvantages. have. If the weight ratio is out of range, the desired effect of the present invention may not be achieved by using a mixture of a single structure powder and a core / shell structure powder.

The negative electrode active material of the present invention may further include conductive fine particles in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the mixture of the powder of the single structure and the powder of the core / shell structure.

The conductive fine particles serve to further improve the electrical conductivity and filling properties of the negative active material mixed powder, specific examples thereof include crystalline carbon (eg, natural graphite, artificial graphite, etc.), carbon black, carbon nanofibers, carbon nanotubes, and the like. And mixtures thereof. The conductive fine particles may preferably have a particle size in the range of 10 nm to 10 μm, more preferably in the range of 50 nm to 5 μm, and when the particle size of the conductive fine particles is less than 10 nm, the reversible capacity may be increased while the filling property is decreased. In addition, even when the particle diameter is larger than 10 mu m, the filling property is not good to decrease.

The negative electrode active material composition of the present invention may be prepared by mixing the negative electrode active material of the present invention in a conventional amount with the conductive fine particles, the binder, the thickener, and the solvent, which are usually used as needed, and the negative electrode active material composition prepared as described above may be prepared. After coating on the surface of the copper current collector, the coating layer may be hot-air dried at 80 to 150 ° C., pressed into a rolling mill, and then vacuum dried at 80 to 150 ° C. for 8 to 12 hours to prepare a negative electrode plate for a lithium secondary battery. The thickness of the prepared negative electrode plate is preferably in the range of 30 to 100㎛ on a cross-sectional basis.

The negative electrode active material according to the present invention improves the filling property during the negative electrode rolling to easily increase the mixture density, less stress on the powder, less powder deformation, the state before the powder is applied when left under a certain condition after rolling The springback phenomenon to return to is greatly reduced. When the springback phenomenon occurs a lot, even though the mixture density increases during rolling, the mixture density decreases in the battery, making it difficult to implement a battery having a high energy density, and also increasing the pressure between electrodes in a battery designed with a constant volume. Induces battery expansion, which can cause battery characteristics and safety degradation. The springback characteristics were measured by measuring the thickness of the negative electrode immediately after rolling (thickness T1) based on the negative electrode mixture density of 1.90 g / cc or less, and measuring the thickness of each negative electrode after vacuum drying for 12 hours after rolling (thickness T2). Can be calculated by applying to [[T2-T1) / T1 * 100], and favorable battery performance can be expressed when this springback characteristic is 8% or less. That is, when the springback characteristic is 8% or more, stress is applied to the positive electrode plate and the battery itself due to excessive volume expansion of the negative electrode plate, and such stress causes electrical non-uniformity, leading to deterioration of battery characteristics.

Winding the electrode stack composed of the negative electrode, the positive electrode and the separator prepared in this way to make a jelly roll (rolling), it is placed in a battery container and sealed a portion (sealing), and then the electrolyte composition in the container The lithium secondary battery containing the negative electrode of this invention can be manufactured by injecting and heating as needed.

As described above, the negative electrode active material of the present invention consisting of a specific combination of mixed powders can maximize the packing density of the negative electrode and minimize the deformation of the negative electrode during intercalation and desorption of lithium. The lithium secondary battery including the negative electrode may exhibit high energy density, excellent battery capacity, and lifetime characteristics.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example 1

A crystalline carbon powder having a monocrystalline crystalline carbon powder having an average volume particle diameter of 15 µm and an amorphous carbon coating layer having a core / shell structure (average volume particle diameter of the core: 17 µm and a thickness of the shell: 0.04 µm) was 1: 0.5. 2 parts by weight of carbon black having an average particle diameter of 100 nm was added as conductive fine particles to 100 parts by weight of the mixture, and used as a negative electrode active material mixed powder. At this time, the crystalline carbon powder having the amorphous carbon coating layer was prepared according to the method disclosed in 2002-57347. 100 parts by weight of the negative active material mixed powder, 2 parts by weight of styrene butadiene rubber (SBR) as a binder, and 2 parts by weight of carboxy methyl cellulose (CMC) as a thickener were mixed with water and sufficiently stirred to prepare a negative electrode active material slurry composition.

The negative electrode active material slurry composition was coated on a surface of a copper current collector using a doctor blade, and then the coating layer was hot-air dried at 110 ° C., roll-pressed to a pressure of 30 kgf / cm ² , and then in a 120 ° C. vacuum oven. By vacuum drying for a time, a negative electrode plate having a thickness of 60㎛ was prepared.

Example 2

A crystalline carbon powder having a monocrystalline crystalline carbon powder having an average volume particle diameter of 20 µm and an amorphous carbon coating layer having a core / shell structure (average volume particle diameter of the core: 18 µm and thickness of the shell: 0.1 µm) was 1: 4. It was mixed by weight ratio and used as a negative electrode active material mixing powder. At this time, the crystalline carbon powder having the amorphous carbon coating layer was prepared according to the method disclosed in 2002-57347.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 1, except that 3 parts by weight of graphite having an average particle diameter of 4 μm was added as the conductive fine particles.

Example 3

A crystalline carbon powder having a single structure having an average volume particle diameter of 25 μm and an amorphous carbon coating layer having a core / shell structure (average volume particle size of the core: 10 μm, thickness of the shell: 0.05 μm) is 1: 1. 3 parts by weight of graphite having an average particle diameter of 4 μm was added as conductive fine particles to 100 parts by weight of the mixture, and used as a negative electrode active material mixed powder. At this time, the crystalline carbon powder having the amorphous carbon coating layer was prepared according to the method disclosed in 2002-57347.

A negative active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 1 using the negative electrode active material mixture.

Comparative Example 1

Only crystalline carbon powder having an amorphous carbon coating layer having a core / shell structure (average volume particle size of the core: 17 μm and shell thickness: 0.04 μm) was used as the negative electrode active material, and as conductive fine particles relative to 100 parts by weight of the negative electrode active material in slurry production. A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 1, except that 2 parts by weight of carbon black having an average particle diameter of 100 nm was added.

Comparative Example 2

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Comparative Example 1 using only crystalline carbon powder having a single structure having an average volume particle diameter of 20 μm as a negative electrode active material.

Comparative Example 3

A crystalline carbon powder having a single structure having an average volume particle diameter of 20 μm and an amorphous carbon coating layer having a core / shell structure (average volume particle size of the core: 18 μm, thickness of the shell: 0.1 μm) of 1: 10.5 The negative electrode active material slurry composition was prepared in the same manner as in Example 2, except that 3 parts by weight of graphite having an average particle diameter of 4 μm was added as conductive fine particles to 100 parts by weight of the negative electrode active material, mixed in a weight ratio, and used as a negative electrode active material. From this, a negative electrode plate was prepared.

Example 4

A crystalline carbon powder having a single structure of crystalline carbon powder having an average volume particle diameter of 25 μm and an AlPO ₄ metal oxide coating layer having a core / shell structure (average volume particle diameter of the core: 10 μm, thickness of the shell: 0.05 μm) was 1: It was mixed by the weight ratio of 1 and used as a negative electrode active material mixing powder. In this case, the crystalline carbon powder having the metal oxide coating layer was prepared as follows. First, 1 g of aluminum oxide and 2 g of diammonium phosphate were mixed and stirred for 2 hours, and then ammonia was added until a gel solution of pH 9 was obtained. 100 g of graphite in powder form having an average particle diameter of 20 μm was added to the resulting gel solution, stirred for 1 hour, dried at 100 ° C. for 24 hours, and calcined at 1200 ° C., to form AlPO ₄ metal oxide-coated crystalline carbon powder. Was prepared.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 2 using the negative electrode active material mixture.

Comparative Example 4

Negative electrode active material slurry composition in the same manner as in Example 4 using only crystalline carbon powder having an AlPO ₄ metal oxide coating layer having a core / shell structure (average volume particle diameter of core: 10 μm, thickness of shell: 0.05 μm) as the negative electrode active material. And a negative electrode plate was prepared therefrom.

Example 5

1: 1 weight ratio between the crystalline carbon powder having a single structure having an average volume particle diameter of 25 μm and the fluorocarbon coating layer having a fluorine coating layer having a core / shell structure (average volume particle size of the core: 10 μm, thickness of the shell: 0.005 μm). It was mixed with and used as a mixed powder of the negative electrode active material. At this time, the crystalline carbon powder having the fluorine coating layer was prepared by treating the crystalline carbon powder with fluorine for 1 hour at 300 ℃.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 2 using the negative electrode active material mixture.

Comparative Example 5

In the same manner as in Example 5, using only the crystalline carbon powder having a fluorine coating layer having a core / shell structure (average volume particle size of the core: 10 mu m, thickness of the shell: 0.005 mu m) as the negative electrode active material, the negative electrode active material slurry composition and the A negative electrode plate was prepared.

Example 6

Si-Cu alloy powder having a single structure of crystalline carbon powder having an average volume particle diameter of 20 μm and an amorphous carbon coating layer having a core / shell structure (average volume particle size of the core: 1 μm, thickness of the shell: 0.05 μm): It mixed at the weight ratio of 0.7 and used it as a negative electrode active material mixing powder. At this time, the alloy powder having the amorphous carbon coating layer was prepared according to the method disclosed in 2002-57347.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 1, except that 2 parts by weight of carbon nanofibers having an average particle diameter of 100 nm was added as the conductive fine particles.

Comparative Example 6

A negative electrode active material slurry composition in the same manner as in Example 6 using only Si-Cu alloy powder having an amorphous carbon coating layer having a core / shell structure (average volume particle size of core: 1 μm, shell thickness: 0.05 μm) as a negative electrode active material And a negative electrode plate was prepared therefrom.

Example 7

Sn-Ni alloy powder having a single structure of crystalline carbon powder having an average volume particle diameter of 20 μm and an amorphous carbon coating layer having a core / shell structure (average volume particle diameter of the core: 10 μm, thickness of the shell: 0.05 μm) 1: It was mixed by the weight ratio of 1 and used as a negative electrode active material mixing powder.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 6 using the negative electrode active material mixture.

Comparative Example 7

Only the Sn-Ni alloy powder having an amorphous carbon coating layer having the core / shell structure (average volume particle diameter of the core: 10 μm, the thickness of the shell: 0.05 μm) shown in Example 7 was used as the negative electrode active material, and was the same as that of Example 7. By the method, a negative electrode active material slurry composition and a negative electrode plate were prepared therefrom.

Example 8

A crystalline carbon powder having a single structure of Sn-Ni alloy powder having an average volume particle diameter of 10 μm and an amorphous carbon coating layer having a core / shell structure (average volume particle size of core: 17 μm, thickness of the shell: 0.04 μm) was 1: It was mixed by the weight ratio of 7 and used as a negative electrode active material mixing powder.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 6 using the negative electrode active material mixture.

Comparative Example 8

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 8 using only Sn-Ni alloy powder having a single structure having an average volume particle diameter of 10 μm as the negative electrode active material powder.

Example 9

LiNiVO ₄ metal oxide powder having a monocrystalline crystalline carbon powder having an average volume particle diameter of 20 μm and an amorphous carbon coating layer having a core / shell structure (average volume particle diameter of the core: 10 μm, thickness of the shell: 0.05 μm) was 1: It mixed at the weight ratio of 0.3 and used as the negative electrode active material mixing powder.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 6 using the negative electrode active material mixture.

Comparative Example 9

A negative electrode active material slurry in the same manner as in Example 9 using only LiNiVO ₄ metal oxide powder having an amorphous carbon coating layer having a core / shell structure (average volume particle diameter of core: 10 μm, thickness of shell: 0.05 μm) as the negative electrode active material powder A composition and a negative plate were prepared therefrom.

Example 10

A crystalline carbon powder having a monolithic LiNiVO ₄ metal oxide powder having an average volume particle diameter of 10 μm and an amorphous carbon coating layer having a core / shell structure (average volume particle diameter of the core: 17 μm, thickness of the shell: 0.04 μm) is 1: 7. It was mixed by the weight ratio of and used as a negative electrode active material mixing powder.

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 6 using the negative electrode active material mixture.

Comparative Example 10

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 10 using only LiNiVO ₄ metal oxide powder having a single structure having an average volume particle diameter of 20 μm as the negative electrode active material powder.

Test Example

Coin-type half cells were manufactured in a conventional manner using the negative electrode plates prepared in Examples 1 to 10 and Comparative Examples 1 to 10, respectively.

The mixture density of the prepared negative electrode plate was measured immediately after rolling. In addition, using a micrometer, the thickness of the negative electrode plate was measured immediately after rolling (thickness T1), and after vacuum drying for 12 hours after rolling (thickness T2), the negative electrode active material was obtained from the formula ((T2-T1) / T1 * 100]. The springback property (%) of was measured. Reversible capacity, initial efficiency, high rate characteristics, and lifetime characteristics of the manufactured batteries were measured, and the results are shown in Table 1 below. After the battery was charged to 0.2C and then discharged to 0.2C, the discharge capacity was "reversible capacity", and the ratio of the discharge capacity to the charging capacity at this time was "initial efficiency", after charging at 2C to the discharge capacity at this time. The ratio of the discharge capacity at the time of discharge at 2.0C was made into "high rate characteristic." The "reversible capacity" is represented by the battery capacity per weight of the negative electrode active material (mAh / g) and the battery capacity per volume when the negative electrode active material is coated (mAh / cc), respectively, the battery capacity per volume is combined with the battery capacity per weight. Obtained by multiplying the density. In other words, as the mixture density increases, the battery capacity per volume becomes larger, and in the battery, the battery capacity per volume becomes a more important capacity value. "Life characteristics" is expressed as a ratio of 50 times the discharge capacity to the first discharge capacity after 50 times the battery was charged to 1.0C and then discharged at 1.0C.

From Table 1, the negative electrode plate prepared in the embodiment of the present invention is superior to the negative electrode plate prepared in the comparative example, the mixture density is high, and when the density is similar, the life characteristics are high, the negative electrode of the present invention It can be seen that the battery having excellent battery performance and lifespan characteristics as compared with the battery having the negative electrode of Comparative Example.

As described above, since the negative electrode active material of the present invention can maximize the filling density of the negative electrode and minimize the deformation of the negative electrode during intercalation and desorption of lithium, the lithium secondary battery including the negative electrode prepared from the negative electrode active material composition including the same. Can exhibit high energy density, excellent battery capacity and lifetime characteristics.

Claims (10)

Single structure powder having no coating layer and core / shell structure powder having coating layer 1: 0.1 to 10 weight ratio, having a spring-back characteristic of 8% or less at a negative electrode mixture density of 1.90 g / cc or less, Anode active material for lithium secondary battery. The method of claim 1, The powder of a single structure is selected from the group consisting of crystalline carbon, amorphous carbon, metals, alloys, metal oxides, metal nitrides, fluorine and mixtures thereof, the negative electrode active material for lithium secondary batteries. The method of claim 1, The powder of a single structure is characterized in that it has an average volume particle size in the range of 0.01 to 40㎛, lithium secondary battery negative electrode active material. The method of claim 1, For lithium secondary battery, characterized in that the powder of the core / shell structure is composed of core and shell components differently selected from the group consisting of crystalline carbon, amorphous carbon, metal, alloy, metal oxide, metal nitride, fluorine and mixtures thereof. Negative electrode active material. The method of claim 4, wherein The powder of the core / shell structure may be crystalline carbon, metal, alloy, metal oxide or metal nitride, having an amorphous or crystalline carbon coating layer; Or crystalline carbon or amorphous carbon having at least one selected from a metal, an alloy, a metal oxide, and fluorine as a coating layer. The method of claim 1, A negative electrode active material for a lithium secondary battery, characterized in that the core of the powder of the core / shell structure has an average volume particle diameter in the range of 0.01 to 40 μm, and the shell has a thickness in the range of 0.001 to 1 μm. The method of claim 1, An anode active material for a lithium secondary battery, characterized in that it further comprises conductive fine particles in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the mixture of the single structure powder and the core / shell structure powder. The method of claim 7, wherein The negative electrode active material for lithium secondary batteries, wherein the conductive fine particles have a particle size in the range of 10 nm to 10 μm. The method of claim 7, wherein Electroconductive fine particles are selected from the group consisting of crystalline carbon, carbon black, carbon nanofibers, carbon nanotubes and mixtures thereof, the negative electrode active material for a lithium secondary battery. A lithium ion-transmission between the negative electrode, the positive electrode, the electrolyte and the electrodes obtained by coating the negative electrode active material composition containing the negative electrode active material of any one of claims 1 to 9 on the surface of the current collector and then drying and compressing the coating layer. Lithium secondary battery comprising a possible separator.