KR101018659B1 - Silicon anode active material for lithium secondary battery - Google Patents

Abstract

The present invention comprises: 100 parts by weight of a silicon metal alloy mixture, i.e., a silicon-based metal alloy mixture which is primarily mechanically processed by mixing at least one metal selected from transition metals, Group 2, Group 13, Group 14 and Group 15 elements with silicon; Ii) 1 to 20 parts by weight of a carbon material powder compound selected from graphite powder, carbon inorganic powder or carbon powder; And iii) 1 to 20 parts by weight of carbon nanofibers, carbon nanotubes or mixtures thereof; iv) a silicon alloy having an average particle size of 0.5 to 30 μm, powdered by secondary mechanically processing 1 to 10 parts by weight of a compound represented by X ₂ CO ₃ (X is an alkali metal selected from Li, Na and K); And it provides a negative electrode active material for a lithium secondary battery prepared by heat-treating the carbon material mixture at 400 to 1200 ℃ 1 to 10 hours. In addition, the negative electrode active material for a lithium secondary battery of the present invention is agglomerated SiM powder during mechanical processing by graphite or carbon powder, the atomization effect and surface improvement effect of the SiM powder is generated, the carbon nano material to improve the conductivity, and also By suppressing the surface side reactions during charging and discharging in the battery by X ₂ CO ₃ , there is an effect of greatly improving the volume expansion problem, the conductivity deterioration problem, the surface side reaction problem, etc., which are disadvantages of the silicon-based negative electrode active material.

Lithium secondary battery, negative electrode active material, carbon nanomaterial, alloy, silicon

Description

Silicon anode active material for lithium secondary battery {Silicon anode active material for lithium secondary battery}

The present invention relates to a negative electrode material for a lithium secondary battery prepared by alloying with a mechanical alloying method between silicon and metal elements. More specifically, in the form of X ₂ CO ₃ composed of alkali metals and carbon nanomaterials such as carbon nanofibers, carbon nanofibers or carbon nanotubes, and carbon powders such as graphite carbon inorganic in the SiM powder coexisting in the form of alloys with silicon and metal elements The present invention relates to a negative electrode material for a lithium secondary battery in which charge and discharge capacity and cycle characteristics are improved by adding a compound (X is an alkali metal).

Li-ion secondary batteries have attracted attention as power sources for driving electronic devices. Graphite is mainly used as a negative electrode material of the lithium ion secondary battery, but graphite has a small capacity of 372 mAh / g per unit mass, and it is difficult to increase the capacity of the lithium ion secondary battery.

As a negative electrode material exhibiting higher capacity than graphite, for example, a material for forming an intermetallic compound with lithium such as silicon, tin, and oxides thereof is promising. However, these materials cause a change in crystal structure when absorbing and storing lithium, causing a problem of expansion of the volume. In the case of silicon, the maximum amount of lithium is absorbed and stored, which is converted to Li _4.4 Si, whereby volume expansion by charging is performed, and in this case, the volume increase rate by charging expands to about 4.12 times the volume of silicon before volume expansion. On the other hand, the volume expansion rate of graphite which is currently used as a cathode material is about 1.2 times.

Therefore, many studies for increasing the capacity of the negative electrode active material such as silicon, that is, researches for reducing the volume expansion rate through alloying of silicon have been conducted, but there was a problem in the practical use, and the main causes are Si, Sn, Al during charge and discharge. This is because metals such as alloying with lithium cause volume expansion and contraction, which causes metal micronization and deterioration in cycle characteristics.

Therefore, in order to improve cycle characteristics, it is proposed to use an amorphous alloy oxide as a negative electrode active material, as described in Y. Idota, et al: Sience, 276, 1395 (1997). In addition, an alloy having an amorphous structure was used as a negative electrode active material, as described in the 43rd Battery Debate Preliminary Proceedings, the Korean Electrochemical Society Battery Technical Committee, October 12, 2014, p. 308-309. In some cases, it is reported that the cycle characteristics are improved.

Silicon, which is known as the element that can be expected to have the highest capacity, is conventionally made of silicon based on the mechanical alloying method, although it is very difficult to conventionally amorphous silicon alone and it is difficult to amorphize the alloy whose main component is silicon. A method has been developed that can easily amorphous the material.

In the case of the amorphous material, since it is not a single structure like the crystalline material, it is known that the expansion rate due to filling is lower than that of the crystalline material and the deterioration due to charge and discharge is less than that of the crystalline material. In addition, the reason why the initial cycle performance is better than that of the crystalline material is particularly complicated by the diffusion passage of lithium ions, and the active material utilization is gradually increased as the number of cycles progresses. This is because the cycle deterioration due to this is alleviated as a result.

Korean Patent Registration No. 10-529103 'Negative Active Material for Lithium Secondary Battery, Manufacturing Method and Lithium Secondary Battery' discloses a method of manufacturing a negative electrode active material for lithium secondary battery using such an amorphous silicon alloy, and more specifically, The silicon and element M powders are alloyed by a mechanical alloying method to form a SiM alloy, and the SiM alloy is heat-treated to cause the powder of element X to be added to the SiM alloy after heat treatment, and alloyed by the mechanical alloying method. A negative electrode active material for a lithium secondary battery, which is manufactured by manufacturing a SiMX alloy and heat treating the SiMX alloy at a temperature lower than a processing temperature in the heat treatment, wherein M is Ni, Co, B, Cr, Cu, Fe. , At least one element selected from the group consisting of Mn, Ti, and Y, and element X is selected from the group consisting of Ag, Cu, and Au. And at least one element selected, Cu discloses a negative active material that is selected at the same time as the element M and the element X.

However, as the number of charge and discharge cycles is further increased in the case of the negative electrode active material for a lithium secondary battery manufactured by the above method, the charge and discharge capacity decreases due to deterioration of the internal silicon, and in the case of the mechanical alloy method disclosed in the patent document, crushing and compression As a result, the deterioration of the interface between microalloy structures which are not distinguished by X-ray diffraction analysis is broken and microstructures are disrupted by occlusion release of lithium.

Of course, these problems are Republic of Korea Patent Registration No. 10-529103 alloying the Si powder and the powder of the element M alloyed by mechanical alloying method and SiM alloying, after the heat treatment of the SiM alloy is added to the powder of the element X to the SiM alloy, This is solved by incorporating this into a mechanical alloying method to form a SiMX alloy, and introducing a process of heat-treating the SiMX alloy at a temperature lower than the temperature in the heat treatment, but the anode material for lithium secondary batteries still alloyed with silicon is sufficient. It did not have the charge and discharge capacity and cycle characteristics was not enough to replace the negative electrode material of the graphite lithium secondary battery.

In the present invention, while continuing to research to significantly improve the charge and discharge capacity and cycle characteristics of the anode material for lithium secondary batteries prepared by alloying with the mechanical alloying method between the silicon and metal elements, alloys with conventionally known silicon and metal elements When adding a carbon powder such as graphite carbon inorganic material, carbon nanomaterial such as carbon nanofibers or carbon nanotubes, and an X ₂ CO ₃ compound composed of an alkali metal (X is an alkali metal) The inventors have found that the charge and discharge capacity and cycle characteristics of a negative electrode material for a secondary battery are remarkably improved, and thus, the present invention has been completed.

The problem to be solved by the present invention is to develop a negative electrode material for a lithium secondary battery that significantly improved the charge and discharge capacity and cycle characteristics of the negative electrode material for a lithium secondary battery prepared by alloying the mechanical alloy method between silicon and metal elements. That is, a X ₂ CO ₃ compound composed of an alkali metal and a carbon nano material such as carbon nanofibers, carbon nanofibers or carbon nanotubes, and an SiM powder coexisting in the form of an alloy with a conventionally known silicon and metal element X is an alkali metal) to develop a negative electrode material for a lithium secondary battery that significantly improved the charge and discharge capacity and cycle characteristics.

An object of the present invention is iii) 100 parts by weight of a silicon metal alloy mixture which is first mechanically powdered by mixing at least one metal selected from transition metals, Group 2, Group 13, Group 14 and Group 15 elements with silicon; Ii) 1 to 20 parts by weight of a carbon material powder compound selected from graphite powder, carbon inorganic powder or carbon powder; And i) a mixture of silicon alloy and carbon material having an average particle size of 0.5 to 30 μm, powdered by secondary mechanical processing of 1 to 20 parts by weight of carbon nanofibers, carbon nanotubes or mixtures thereof at 400 to 1200 ° C. It is to provide a negative electrode active material for a lithium secondary battery prepared by heat treatment for 1 to 10 hours.

In addition, the negative electrode active material for a lithium secondary battery is characterized in that it may further comprise 1 to 10 parts by weight of a compound represented by X ₂ CO ₃ (X is an alkali metal selected from Li, Na, K).

In addition, the metal is characterized in that the transition metal selected from Cu, Zr, Ni, Ti, Co, Cr, V, Mn and Fe.

Meanwhile, the carbon nanofibers or carbon nanotubes have an island diameter of 5 to 500 nm and an aspect ratio of 10 to 1000.

In addition, the heat treatment temperature is characterized in that the heat treatment in the 400 to 1200 ℃ temperature range of 20 to 100 ℃ or less than the Tm of the silicon alloy.

Still another object of the present invention is to provide a negative electrode for a lithium secondary battery prepared by mixing a binder and a conductive material with the negative electrode active material for a lithium secondary battery.

An effect of the present invention is to provide a negative electrode material for a lithium secondary battery that significantly improved the charge and discharge capacity and cycle characteristics of the negative electrode material for a lithium secondary battery prepared by alloying the mechanical alloy between silicon and metal elements. That is, a X ₂ CO ₃ compound composed of an alkali metal and a carbon nano material such as carbon nanofibers, carbon nanofibers or carbon nanotubes, and an SiM powder coexisting in the form of an alloy with a conventionally known silicon and metal element X is an alkali metal) to provide a negative electrode material for a lithium secondary battery in which charge and discharge capacity and cycle characteristics are remarkably improved.

In addition, the negative electrode active material for a lithium secondary battery of the present invention is agglomerated SiM powder during mechanical processing by graphite or carbon powder, the atomization effect and surface improvement effect of the SiM powder is generated, the carbon nano material to improve the conductivity, and also By suppressing the surface side reactions during charging and discharging in the battery by X ₂ CO ₃ , there is an effect of greatly improving the volume expansion problem, the conductivity deterioration problem, the surface side reaction problem, etc., which are disadvantages of the silicon-based negative electrode active material.

The present invention is described in more detail below.

The present invention relates to a negative electrode active material for a lithium secondary battery, comprising: graphite in SiM powder in which silicon and alloy coexist by mechanically processing M, which is one of transition metal, group 2, group 13, group 14, and group 15 elements in silicon together. To a carbon powder, a carbon nano material, and X ₂ CO ₃ composed of an alkali metal X, and then manufactured by mechanical processing.

In the negative electrode active material of the present invention, the SiM powder agglomerated during mechanical processing is produced by the atomization effect and surface improvement effect of the SiM powder by graphite or carbon powder, and the conductivity improvement effect is generated by the carbon nanomaterial, and X ₂ By suppressing the surface side reactions during the charging and discharging in the battery by CO ₃ , it greatly improves the problems of the volume expansion problem, conductivity deterioration problem, surface side reaction problems and the like disadvantages of the silicon-based negative electrode active material.

In addition, the lithium secondary battery including an electrode prepared from the negative electrode active material composition of the present invention exhibits excellent battery capacity, lifetime characteristics, and high safety.

In the silicon alloy composition of the present invention, Si is mixed with one or more metals selected from transition metals, Group 2, Group 13, Group 14, and Group 15 elements to be mechanically processed and powdered. At this time, the amount of silicon is preferably added more than the metal element M and the chemical capacity ratio. If the amount of silicon is smaller than the chemical capacity ratio of M, the amount of silicon is insufficient, so that the silicon phase which precipitates into the SiM phase and the M phase and contributes during charging and discharging is not precipitated, so charging and discharging cannot be performed.

On the other hand, when the amount of silicon is added excessively, a large amount of silicon phase is precipitated, and the amount of expansion and shrinkage of the entire negative electrode active material increases during charging and discharging, and the negative electrode active material tends to be undifferentiated, resulting in a decrease in cycle characteristics. Preferably, the range of 40 mass% or more and 80 mass% or less of silicon composition ratio in a silicon alloy composition is preferable.

In the alloying process through mechanical processing, a mixture of Si powder and one or more metal powders selected from transition metals, Group 2, 13, 14, and 15 elements is powdered and alloyed by a mechanical alloying method. As the silicon powder, for example, an average particle diameter of 1 to 100 µm is used, and as the metal powder, an average particle diameter of 1 to 50 µm is used. Such a Si powder and one or more metal powders selected from transition metals, Group 2, 13, 14, and 15 elements are added to, for example, a ball mill and a wet batch, and subjected to a mechanical alloy that is repeatedly pulverized and compressed. Alloying is carried out. This obtains an alloy powder of silicon and metal. The mechanical alloying is preferably carried out until the SiM alloy is amorphous.

Looking at the composition of the negative electrode active material for a lithium secondary battery used in the present invention iii) powdered by first mechanically processing by mixing at least one metal selected from transition metals, Group 2, 13, 14, Group 15 elements to silicon 100 parts by weight of the silicon metal alloy mixture; Ii) 1 to 20 parts by weight of a carbon material powder compound selected from graphite powder, carbon inorganic powder or carbon powder; And iii) 1 to 20 parts by weight of carbon nanofibers, carbon nanotubes or mixtures thereof; Is a mixture of silicon alloys and carbon materials having an average particle size of 0.5 to 30 μm, powdered by secondary mechanical processing.

In addition, the metal is preferably a transition metal selected from Cu, Zr, Ni, Ti, Co, Cr, V, Mn and Fe.

Also optionally, the silicon alloy and carbon material mixture may further include 1 to 10 parts by weight of a compound represented by X ₂ CO ₃ (X is an alkali metal selected from Li, Na, K). Preferred compounds are Li ₂ CO ₃ and the preferred content is about 3 to 8 parts by weight.

The mixture of the silicon alloy and the carbon material having the above composition is thermally baked at 400 to 1200 ° C. for 1 to 10 hours to prepare a negative active material for a lithium secondary battery.

At this time, a preferable heat processing temperature is 20-100 degreeC or less than Tm of a silicon alloy.

On the other hand, the carbon nanofibers or carbon nanotubes used at this time are 5 to 300 nm in diameter, and the aspect ratio is preferably 10 to 1000.

The present invention will be described in more detail with reference to the following examples. However, these examples do not limit the scope of the present invention.

Preparation Example 1 Preparation of Anode Active Material

15 g of Si powder (from China, more than 99.9% purity, classification of # 270 sieve) and 15 g of Cu powder (Aldrich, more than 99% purity) were mixed and ground for 8 hours in an argon atmosphere with a planetary mill (Fritzch, Germany). Thereafter, 1.5 g of graphite powder (from China, purity of 99.9% or more) and 1.5 g of carbon nanofibers (100 nm of diameter) were mixed, and further ground for 30 minutes under an argon atmosphere with specsmill to prepare a negative electrode active material powder. The particle size of the powder obtained was analyzed using a laser diffraction particle size analyzer (Symptatec GmbH, Germany), and the results are shown in Table 1.

80 parts by weight of the negative electrode active material, 15 parts by weight of polyvinylidene fluoride dissolved in a 10% N-methylpyrrolidone solvent as a binder, and 10 parts by weight of acetylene black as a conductive material were mixed together and stirred sufficiently to prepare a negative electrode active material slurry composition. Prepared.

The slurry composition was coated on a OHP film with a doctor blade, and the coating layer was hot-air dried at 80 ° C., roll-pressed to a pressure of 30 kgf / cm 2, and then using a surface resistance analyzer (Mitsubishi Chemical, Japan). The electrical resistance was measured, and the results are shown in Table 1. The electrode mixture density at this time was manufactured so that it might be 1.5 +/- 1.0 g / cc.

Preparation Example 2 Preparation of Anode Active Material

18 g of Si powder (from China, more than 99.9% purity, # 270 sieve classification) and 12 g of Fe powder (from China, more than 99.9% purity, # 270 sieve classification) are mixed, and in an argon atmosphere with a specmill (Fritzch, Germany) After grinding for 6 hours, 3 g of graphite powder (made in China, purity of 99.9% or more) and 4 g of carbon nanotubes (25 nm of island diameter) were mixed, and further ground for 30 minutes under an argon atmosphere with a spec mill. The pulverized powder was heat-treated at 780 ° C. for 5 hours in a tube-type heat treatment furnace replaced with a nitrogen atmosphere, thereby preparing a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

Preparation Example 3 Preparation of Anode Active Material

18 g of Si powder (from China, 99.9% purity, # 270 sieve classification) and 12 g of Ti powder (Alfa, 99% purity, 325 mesh) were mixed and ground for 6 hours in an argon atmosphere with a Speczmill (Fritzch, Germany). Thereafter, 4 g of graphite powder (made in China, purity of 99.9% or more), 4 g of carbon nanofibers (100 nm of diameter), and ₂ g of Li ₂ CO ₃ were mixed, and further ground for 30 minutes in an argon atmosphere with a specmill to prepare a negative electrode active material powder. .

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

Preparation Example 4 Preparation of Anode Active Material

20 g of Si powder (from China, more than 99.9% purity, # 270 sieve classification) and 10 g of Mg powder (Aldrich, more than 99% purity) were mixed and ground for 10 hours in an argon atmosphere with a planetary mill (Fritzch, Germany). Thereafter, 2 g of coke powder (made in Japan, needle coke) and 2 g of carbon nanotubes (25 nm of diameter) were mixed, and further ground in an argon atmosphere with a planetary mill for 30 minutes. The pulverized powder was heat-treated at 600 ° C. for 5 hours in a tube-type heat treatment furnace replaced with a nitrogen atmosphere, thereby preparing a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

Preparation Example 5 Preparation of Anode Active Material

20 g of Si powder (from China, more than 99.9% purity, classification of # 270 sieve) and 10 g of Ni powder (Aldrich, more than 99% purity) are mixed and ground in an argon atmosphere with an oscillating mill (ITOH, Japan) for 20 hours. , 3 g of pitch (made in China, softening point 220 ⁰ C) and 3 g of carbon nanofibers (100 nm diameter) were mixed, and further ground in an argon atmosphere with a vibration mill for 2 hours. The pulverized powder was heat-treated at 600 ° C. for 5 hours in a tube-type heat treatment furnace replaced with a nitrogen atmosphere, thereby preparing a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

(Comparative Example 1) Preparation of anode active material (graphite, carbon nanofibers not present)

15 g of Si powder and 15 g of Cu powder were mixed, and ground with an planetary mill (Fritzch, Germany) for 8 hours and 30 minutes in an argon atmosphere to prepare a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

Preparation Example 2 Preparation of Anode Active Material (Presence of Carbon Nanotubes)

18 g of Si powder (from China, more than 99.9% purity, # 270 sieve classification) and 12 g of Fe powder (from China, more than 99.9% purity, # 270 sieve classification) are mixed, and in an argon atmosphere with a specmill (Fritzch, Germany) After grinding for 6 hours, 7 g of graphite powder (from China, purity of 99.9% or higher) was mixed, and further ground for 30 minutes under an argon atmosphere with a specmill. The pulverized powder was heat-treated at 780 ° C. for 5 hours in a tube-type heat treatment furnace replaced with a nitrogen atmosphere, thereby preparing a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, the slurry composition was prepared, the coating layer was prepared, and the electrical resistance was measured. The results are shown in Table 1.

Preparation Example 3 Preparation of Anode Active Material (M-free)

30 g of Si powder (from China, more than 99.9% purity, classification of # 270 sieve) was pulverized for 6 hours in argon atmosphere with speczmill (Fritzch, Germany), and then 4 g of graphite powder (from China, more than 99.9% purity) and carbon nanofiber (100 nm diameter) 4 g and ₂ g of Li ₂ CO ₃ were mixed, and further ground for 30 minutes in an argon atmosphere with a specmill to prepare a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

Preparation Example 4 Preparation of Cathode Active Material (Presence of Coke and Carbon Nanotubes)

20 g of Si powder (from China, 99.9% purity, # 270 sieve classification) and 10 g of Mg powder (Aldrich, 99% purity or more) were mixed, and the planetary mill (Fritzch, Germany) was used for 10 hours and 30 minutes in an argon atmosphere. After grinding, heat treatment was performed for 5 hours at 600 ° C. in a tube-type heat treatment furnace replaced with a nitrogen atmosphere to prepare a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

Preparation Example 5 Preparation of Negative Electrode Active Material (Presence of Pitch and Carbon Nanofibers)

20 g of Si powder (from China, 99.9% purity, # 270 sieve classification) and 10 g of Ni powder (Aldrich, 99% purity or more) are mixed and pulverized for 22 hours in an argon atmosphere with a vibrating mill (ITOH, Japan). In a tube-type heat treatment furnace substituted with a nitrogen atmosphere, heat treatment was performed at 600 ° C. for 5 hours to prepare a negative electrode active material powder.

The negative electrode active material was analyzed for particle size in the same manner as in Preparation Example 1, slurry composition preparation, coating layer preparation and electrical resistance were measured, and the results are shown in Table 1.

(Examples 1 to 5) secondary battery charge and discharge test

The negative electrode active material slurry composition prepared in Preparation Examples 1 to 5 was coated on the surface of a copper current collector using a doctor blade, and then the coating layer was hot-air dried at 120 ° C., 30 kgf / cm 2. The negative electrode plate was prepared by roll-pressing under pressure and then vacuum drying in a 120 ° C. vacuum oven for 12 hours.

After measuring the discharge capacity, the initial efficiency, the 1C / 0.2C high rate, the capacity reduction rate, etc. of the prepared secondary battery negative electrode is shown in Table 2. The amount of 1C current was 1,000mAh, and the discharge capacity was calculated as the volumetric capacity of the cathode active material only at 0.2C first charge and discharge, and the capacity reduction rate was the percentage of the third discharge capacity to the first discharge capacity at 0.2C. It is represented as.

(Comparative Example 1)

As a result of analysis of the negative electrode active material prepared in Comparative Preparation Example 1, the volume content of the particle size of 1 um or less is 9.6%, d ₅₀ , that is, the average particle size is 9.2um, d _max , that is, the maximum particle size is 46.6um. The resistance was found to be 135 ohm / sq. It can be seen that both the particle size and the electrical resistance are larger than in Preparation Example 1. This is due to the difference between the powder atomization effect by the impression graphite and the conductivity improvement effect by the CNF, thereby exhibiting a decrease in the overall secondary battery electrical properties.

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

The discharge capacity, initial efficiency, 1C / 0.2 high rate, capacity reduction rate, and the like of the manufactured secondary battery negative electrode were measured and shown in Table 2 below.

(Comparative Example 2)

As a result of analysis of the negative electrode active material prepared in Comparative Example 2, it was found that the volume content of the particles having a particle size of 1 μm or less was 22.4%, d ₅₀ was 4.9 μm, d _max was 38.9 μm, and the electrical resistance was 189 ohm / sq. Although the particle size is similar to that of Preparation Example 2, it can be seen that the electrical resistance is more than two times larger. This is due to the difference in the conductivity improvement effect by CNF, and due to this the degradation of the high rate characteristics of the secondary battery electrical properties was noticeable.

The discharge capacity, initial efficiency, 1C / 0.2 high rate, capacity reduction rate, and the like of the manufactured secondary battery negative electrode were measured and shown in Table 2 below.

(Comparative Example 3)

As a result of analysis of the negative electrode active material prepared in Comparative Example 3, it was found that the volume content of the particle size of 1 um or less is 18.2%, d ₅₀ is 2.6um, d _max is 29.4um, and the electrical resistance is 56 ohm / sq. The particle size and electrical conductivity are similar to those of Preparation Example 3. However, the difference in the initial efficiency of the electrical properties tends to be large, which can be seen to be caused by Li ₂ CO ₃ .

The discharge capacity, initial efficiency, 1C / 0.2 high rate, capacity reduction rate, and the like of the manufactured secondary battery negative electrode were measured and shown in Table 2 below.

(Comparative Example 4)

As a result of analysis of the negative electrode active material prepared in Comparative Example 4, the volume content of the particle size was less than 1 um, 8.2%, d ₅₀ was 9.0um, d _max was 49.2um, and the electrical resistance was 350 ohm / sq. It can be seen that the electrical resistance is a large difference compared to the manufacturing example 4. This is due to the difference in conductivity enhancement effect by CNTs, which results in a large difference in high-rate characteristics and a difference in initial efficiency due to surface properties due to coke, resulting in a difference in discharge capacity and capacity reduction rate. It became.

The discharge capacity, initial efficiency, 1C / 0.2 high rate, capacity reduction rate, and the like of the manufactured secondary battery negative electrode were measured and shown in Table 2 below.

(Comparative Example 5)

As a result of analysis of the negative electrode active material prepared in Comparative Example 5, it was found that the volume content of the particles having a particle size of less than 1 um was 4.2%, d ₅₀ was 10.2 um, d _max was 55.9 um, and the electrical resistance was 368 ohm / sq. It can be seen that the small increase in particle size and the large increase in electrical resistance compared to Preparation Example 5. Due to the difference in the conductivity enhancement effect by the CNF, the high rate characteristic was a big difference, the difference in the initial efficiency due to the difference in the surface properties by the pitch, resulting in a difference in discharge capacity and capacity reduction rate.

The discharge capacity, initial efficiency, 1C / 0.2 high rate, capacity reduction rate, and the like of the manufactured secondary battery negative electrode were measured and shown in Table 2 below.

division Discharge capacity
(mAh / cc) Initial efficiency
(%) 1C / 0.2C high rate
(%) Capacity reduction rate
(%) Example 1 1032 81.3 87.5 4.5 Comparative Example 1 1221 70.5 31.2 70.2 Example 2 1080 80.2 83.5 7.3 Comparative Example 2 1075 79.9 83.2 25.8 Example 3 1105 86.5 87.7 4.7 Comparative Example 3 1462 45.3 15.5 86.3 Example 4 1215 73.3 81.3 9.8 Comparative Example 4 837 65.9 45.2 61.3 Example 5 902 74.6 84.7 7.1 Comparative Example 5 721 65.6 35.5 72.1

1 is a photograph of the powder prepared in Example 1 coated on a copper current collector and dried and then coated with FE-SEM.

Claims (6)

Iii) 100 parts by weight of a silicon metal alloy mixture which is first mechanically powdered by mixing at least one metal selected from Cu, Zr, Ni, Ti, Co, Cr, V, Mn or Fe with silicon; Ii) 1 to 20 parts by weight of a carbon material powder compound selected from graphite powder, carbon inorganic powder or carbon powder; V) 1 to 20 parts by weight of carbon nanofibers, carbon nanotubes or mixtures thereof; And V) 1 to 10 parts by weight of a compound represented by X ₂ CO ₃ (X is an alkali metal selected from Li, Na, K); The silicon alloy and carbon material mixture having a mean particle size of 0.5 to 30 占 퐉 powdered by secondary mechanical processing was heat-treated for 1 to 10 hours in the temperature range of 400 to 1300 ° C., which is 20 to 100 ° C. or less than the Tm of the silicon alloy. Manufactured negative electrode active material for lithium secondary battery delete delete The negative electrode active material of claim 1, wherein the carbon nanofibers or carbon nanotubes have an island diameter of 5 to 500 nm and an aspect ratio of 10 to 1000. delete The negative electrode for a lithium secondary battery manufactured by mixing a binder and a conductive material in the negative electrode active material for a lithium secondary battery of claim 1

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