KR100663182B1 - Anode active material for lithium secondary battery having high energy density - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery, characterized in that it comprises a unstructured single structure powder and a surface / oxidized core / shell structure powder 1: 0.1-10 weight ratio after coating, and the negative electrode of the present invention. A lithium secondary battery including a negative electrode prepared from a negative electrode active material composition containing an active material exhibits high energy density, excellent battery capacity, and lifespan characteristics.

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, the present invention provides a negative electrode active material for a lithium secondary battery, including a unstructured single structure powder and a surface / oxidized core / shell structure powder 1: 0.1-10 weight ratio after coating.

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 contains as a negative electrode active material a combination of a 1: 0.1 to 10 weight ratio of a single structure powder that is not coated and surface-treated and a core / shell structure (multilayer structure) powder that is surface-oxidized after coating. Characterized in that.

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 surface-oxidized core / shell structure powder after coating, which can be used as the negative electrode active material in the present invention, is differently selected from the group consisting of crystalline carbon (eg, natural graphite, artificial graphite, etc.), amorphous carbon, and mixtures thereof. Core and shell components, and preferred examples thereof include crystalline carbon having an amorphous carbon coating layer, amorphous carbon having an amorphous carbon coating layer, crystalline carbon having a crystalline carbon coating layer, amorphous carbon having a crystalline carbon coating layer, and the like. 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.

After coating, the surface-oxidized core / shell structure powder can be prepared by coating the surface of a single structure powder (core component) with a heterogeneous powder (shell component) by conventional wet or dry method and then further oxidizing the surface. have. Specifically, the precursor and the shell component of the core component are mixed and refluxed in an organic solvent, followed by filtration and heat treatment (wet method, see Korean Patent Publication No. 1999-80594), or the powdery core component and the powdery shell component. After physically generating heat by mixing, the coating may be performed by heat treatment in two steps at 500 to 2800 ° C. for 1 to 6 hours (dry method, see Korean Patent Publication No. 2002-57347). Subsequently, the coated powder may be subjected to oxidation treatment of the surface of the coated powder by flowing oxygen-containing gas such as oxygen, air and ozone at a temperature of 150 to 800 ° C. for 10 to 120 minutes, preferably The oxygen-containing gas may be contacted with the coated powder surface at a rate of 0.1-50 L / sec.

The powder having a single structure has an advantage of having high expandability at intercalation and desorption of lithium and causing a lot of irreversible reactions at the interface between the powder and the electrolyte, while increasing packing density and electrical conductivity at the time of electrode rolling. On the other hand, the powder of the core / shell structure subjected to the surface oxidation after coating has a disadvantage in that, in contrast to the physical properties of the powder of a single structure, it has a disadvantage in terms of mixture density and electrical conductivity due to its low filling property during electrode rolling. When inserted and detached, the expandability is small and rarely causes irreversible reaction, and fine surface bending is formed on the surface through the surface oxidation to improve the wettability with the electrolyte. According to the present invention, by using a mixture of the negative electrode active material powder of the unstructured single structure and the negative electrode active material powder of the surface-oxidized core / shell structure after coating in a ratio of 1: 0.1 to 10 by weight, It can compensate for the shortcomings. If it is out of the weight ratio range, it is impossible to achieve the desired effect of the present invention according to the mixed use of the single structure powder and the surface-oxidized core / shell structure powder.

The negative electrode active material of the present invention may further include the 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 subjected to the surface oxidation treatment.

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.

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

As described above, the negative electrode active material of the present invention composed of a mixed powder of a specific combination can maximize the filling density of the negative electrode, minimize the deformation of the negative electrode during intercalation and desorption of lithium, and can increase the wettability of the electrolyte. A lithium secondary battery including a negative electrode prepared from a negative electrode active material composition including the same 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

Crystalline carbon having a single structure of crystalline carbon powder having an average volume particle diameter of 16 μm and an amorphous carbon coating layer having a surface / oxidized core / shell structure (average volume particle diameter of the core: 15 μm, thickness of the shell: 0.03 μm) after coating. The powder was mixed in a weight ratio of 1: 1, and 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 an amorphous carbon coating layer formed by coating was obtained according to the method disclosed in 2002-57347, and the oxidation treatment of the coated powder surface was carried out at a rate of 0.5 l / sec for the coated powder. It was carried out by flowing for 60 minutes at a temperature of 500 ℃. 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. It was vacuum dried for a time to prepare a negative electrode plate having a thickness of 60㎛.

Comparative Example 1

In Example 1, the crystalline carbon powder having an amorphous carbon coating layer was used without a separate surface oxidation treatment, and 2 parts by weight of carbon black having an average particle diameter of 100 nm as conductive fine particles compared to 100 parts by weight of the negative electrode active material at the time of slurry production, not during the production of the negative electrode active material. Except for the addition of the negative electrode active material slurry composition and a negative electrode plate was prepared in the same manner as in Example 1.

Example 2

Crystalline carbon 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 surface / oxidized core / shell structure (average volume particle size of core: 17 μm, thickness of the shell: 0.06 μm) after coating. The powder was mixed in a weight ratio of 1: 9 and used as a negative electrode active material mixed powder. At this time, the crystalline carbon powder having an amorphous carbon coating layer formed by the coating was obtained according to the method disclosed in 2002-57347, and the oxidation treatment of the coated powder surface gave air at a rate of 750 at a rate of 30 l / sec for the coated powder. It was carried out by flowing for 30 minutes at a temperature of ℃.

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 graphite having an average particle diameter of 4 μm was added as the conductive fine particles.

Comparative Example 2

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 2, except that the weight ratio of the negative electrode active material mixed powder in Example 2 was mixed to be 1:11.

Comparative Example 3

In the same manner as in Example 2, only crystalline carbon powder having an amorphous carbon coating layer having a surface / oxidized core / shell structure (average volume particle diameter of core: 17 μm, thickness of shell: 0.06 μm) after coating was used as the negative electrode active material. A negative electrode active material slurry composition and a negative electrode plate were prepared therefrom.

Example 3

Amorphous carbon having a single structure of crystalline carbon powder having an average volume particle diameter of 16 μm and an amorphous carbon coating layer having a surface / oxidized core / shell structure (average volume particle size of the core: 15 μm, thickness of the shell: 0.07 μm) after coating. The powder was mixed in a weight ratio of 1: 1 and used as a negative active material mixed powder.

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

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 3, except that amorphous carbon powder having an amorphous carbon coating layer was used in Example 3 without a separate surface oxidation treatment.

Example 4

Amorphous carbon having a single structure of amorphous carbon powder having an average volume particle diameter of 15 μm, and an amorphous carbon coating layer having a surface / oxidized core / shell structure (average volume particle diameter of the core: 15 μm, thickness of the shell: 0.07 μm) after coating. The powder was mixed in a weight ratio of 1: 0.8 and used as a negative electrode active material mixed powder.

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

A negative electrode active material slurry composition and a negative electrode plate were prepared in the same manner as in Example 4, except that amorphous carbon powder having an amorphous carbon coating layer was used in Example 4 without a separate surface oxidation treatment.

Test Example

Coin-type half cells were manufactured in a conventional manner using the negative electrode plates prepared in Examples 1 to 4 and Comparative Examples 1 to 5, respectively.

The mixture density of the prepared negative electrode plate was measured after vacuum drying for 12 hours after rolling, and the reversible capacity, initial efficiency, high rate characteristics, and lifetime characteristics of the manufactured cells 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. That is, the larger the mixture density, the larger the battery capacity per volume, and in the cell, 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 has a higher density than the negative electrode plate prepared in the comparative example, and when the density is similar, the life characteristics are high, so that the battery having the negative electrode of the present invention is the negative electrode of the comparative example It can be seen that both high rate charge and discharge characteristics and cycle life characteristics are superior to the battery having.

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

Claims (11)

A non-surface single structure powder and a surface / oxidized core / shell structure powder after coating 1: 0.1-10 weight ratio, The negative electrode active material for lithium secondary batteries. 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, The powder of the core / shell structure is made of a core and a shell component differently selected from the group consisting of crystalline carbon, amorphous carbon and mixtures thereof, the negative electrode active material for a lithium secondary battery. 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, The surface oxidation treatment of the coated powder after coating is carried out for 10 to 120 minutes at a temperature of 150 to 800 ℃ using an oxygen-containing gas selected from oxygen, air and ozone, lithium secondary battery negative electrode active material. The method of claim 6, An oxygen-containing negative electrode active material, characterized in that for contacting the coated powder at a rate of 0.1 to 50L / sec. The method of claim 1, An anode active material for 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 monostructure powder and the surface-oxidized core / shell structure powder. The method of claim 8, 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 8, 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 comprising the negative electrode active material of any one of claims 1 to 10 on the surface of the current collector and then drying and compressing the coating layer. Lithium secondary battery comprising a possible separator.