KR100277792B1 - Anode Active Material for Lithium-Based Battery and Manufacturing Method Thereof - Google Patents

Abstract

The present invention provides an anode active material for lithium-based batteries that can improve the packing density of the electrode plate and has good high-rate charge-discharge characteristics and long-life characteristics. The amorphous carbon precursor solution is prepared by dissolving or dispersing an amorphous carbon precursor in a solvent. One or more crystalline carbon primary particles are coated and granulated using and then spherical to prepare secondary particles. Subsequently, the secondary particles are carbonized so that at least one crystalline carbon primary particle is coated with amorphous carbon, and the primary particles coated with the amorphous carbon are assembled to form a substantially spherical secondary particle to provide a negative electrode active material for a lithium-based battery. do.

Description

Anode Active Material for Lithium-Based Battery and Manufacturing Method Thereof

Industrial use field

The present invention relates to a negative electrode active material for a lithium-based battery and a method for manufacturing the same, and more particularly, to a negative electrode active material for a lithium-based battery and a method for manufacturing the same, which can improve the packing density of the electrode plate and have good high rate charge / discharge characteristics and lifetime characteristics. will be.

Prior art

The carbon active material is mainly used as a negative electrode active material of a lithium type battery, especially a lithium ion battery or a lithium ion polymer battery. This carbon active material is largely classified into a crystalline carbon active material and an amorphous carbon active material. The crystalline carbon active material includes natural graphite, and artificial graphite obtained by firing a pitch or the like at a high temperature of 2000 ° C or higher. An amorphous carbon active material is a carbon active material having low graphitization degree or almost no diffraction line in X-ray diffraction, and hard carbon obtained by firing polymer resins such as soft carbon and phenol resin obtained by firing coal pitch or petroleum pitch. have.

In order to apply crystalline carbon active materials such as natural graphite and artificial graphite to a battery, a pulverization and classification process is performed. At this time, an amorphous or plate-like active material is inevitably generated due to the high degree of crystallization of the crystalline carbon active material. When the amorphous or plate-like crystalline carbon active material is applied to the electrode plate as it is, its shape shows low tap density. In addition, when the active material is filled in the electrode plate and pressed, the amorphous active material particles are completely oriented so that only the basal plane, which is not suitable for insertion and desorption of lithium ions, is exposed to the electrolyte, thereby degrading high rate charge / discharge characteristics. The volumetric expansion and contraction of the pole plate increases, which degrades the life characteristics. In addition, the crystalline carbon active material is difficult to be applied to a lithium-based secondary battery that requires high initial efficiency because a graphene sheet is well developed at the edge portion and severe side reaction with the electrolyte is required (Journal of Electrochemical Society 137 (1990). ) 2009).

In order to solve these problems, US Patent No. 5,344,726 proposes a method of increasing the initial charge and discharge efficiency by applying an amorphous carbon layer on the surface of the high crystalline carbon material to suppress the decomposition reaction of the electrolyte. However, this method is so thin that the thickness of the amorphous carbon layer makes it difficult to improve the shape of low-cost amorphous or plate-shaped crystalline carbon nuclei and still cannot improve the packing density of the electrode plate. In addition, in the pressing step of the electrode plate, the high crystalline graphite, which is the nucleus of the amorphous active material, is completely oriented, thereby degrading high rate charge and discharge characteristics and life characteristics.

U.S. Patent 5,401,598 proposes a method of preparing a carbon active material having a multilayer structure by introducing a pitch into the graphite surface by boiling the graphite powder in a mixed solution of pitch and toluene, and then molding and carbonizing the pitch. Since the content of the amorphous portion is 35% by volume or more, the voltage flatness is poor due to the excessive amount of amorphous carbon. In addition, the manufacturing method according to the present invention by carbonizing and grinding the mixture of the amorphous carbon precursor bulk and the graphite particles, the interface between the amorphous carbon and the graphite particles is exposed to the surface can not substantially obtain the effect of coating the amorphous carbon. This leads to a decrease in initial charge and discharge efficiency due to side reaction with the electrolyte.

In addition, the packing density of the electrode plate and the high rate filling method, such as a method of adding a conductive agent to the active material, a method of manufacturing a composite electrode plate using a metal capable of forming a metal film having excellent conductivity, and a method of mixing two or more active materials. Various attempts have been made to improve discharge characteristics and lifetime characteristics, but the effects have not been sufficient.

In order to solve this problem, an object of the present invention is to provide a negative electrode active material for a lithium-based battery that can improve the packing density of the electrode plate without deterioration of electrochemical properties such as high rate charge and discharge characteristics.

Another object of the present invention is to provide a negative electrode active material for a lithium-based battery having excellent voltage flatness and good high rate charge / discharge characteristics and lifetime characteristics.

Still another object of the present invention is to provide a method of manufacturing the negative electrode active material.

1 is a cross-sectional view of a negative electrode active material according to an embodiment of the present invention.

Figure 2A is a SEM photograph of the negative electrode active material according to an embodiment of the present invention.

Figure 2B is a SEM photograph of the electrode plate made of a negative electrode active material according to an embodiment of the present invention.

3A is a SEM photograph of a negative electrode active material according to a comparative example of the present invention.

Figure 3B is a SEM photograph of the electrode plate made of a negative electrode active material according to a comparative example of the present invention.

In order to achieve the object of the present invention, the present invention to prepare an amorphous carbon precursor solution by dissolving or dispersing an amorphous carbon precursor in a solvent, and coating and assembling one or more crystalline carbon primary particles with the amorphous carbon precursor solution And then spheroidized to produce secondary particles, and then carbonizing the spherical secondary particles, one or more crystalline carbon primary particles are coated with amorphous carbon, and the primary particles coated with amorphous carbon are assembled (造粒). It provides a negative electrode active material for a lithium-based battery, characterized in that) to form a substantially spherical secondary particles.

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

As the amorphous carbon precursor, a polymer resin such as coal pitch, petroleum pitch, coal oil, petroleum heavy oil or phenol resin, furan resin or polyimide resin can be used. It is preferable to use coal pitch or petroleum pitch to have a higher capacity and a small irreversible capacity. At this time, toluene or tetrahydrofuran solubility obtained by dissolving and extracting coal pitch or petroleum pitch and polymer resin in toluene, tetrahydrofuran, etc. It is more preferable to use pitch.

As a solvent for dissolving or dispersing the amorphous carbon precursor, an organic solvent, an inorganic solvent, or the like can be used, and examples thereof include toluene, tetrahydrofuran, benzene, methanol, ethanol, hexane, cyclohexane, water, and the like. In some cases, a mixture thereof may be used.

As the crystalline carbon primary particles, inexpensive amorphous or plate-like crystalline carbon particles may be used. In addition, plate-like, lean flake, spherical or fibrous carbon particles may be used alone or in combination of two or more. Of course, as this crystalline carbon, both natural graphite and artificial graphite can be used. The average size of the crystalline carbon primary particles is preferably 0.1-30 μm.

The process of coating and assembling one or more crystalline carbon primary particles with an amorphous carbon precursor solution involves mixing and agglomeration of the crystalline carbon primary particles with an amorphous carbon precursor solution, or the amorphous carbon precursor to the crystalline carbon primary particles. The solution is spray dried or spray pyrolysis. Subsequently, the spherical secondary particles are carbonized at 700-1400 ° C. so that at least one crystalline carbon primary particle 1 is coated with amorphous carbon 2 as shown in FIG. 1, and the primary particles coated with amorphous carbon are An active material which is granulated to form substantially spherical secondary particles is provided. A microporos channel 3 may be formed between the crystalline carbon primary particles coated with amorphous carbon.

It is preferable that the particle size of this negative electrode active material is 5-100 micrometers, More preferably, it is 10-65 micrometers. If the particle size is more than 100 μm, it is difficult to exhibit a preferable electrode plate filling density, and if the particle size is less than 5 μm, there is a fear of causing undesirable side reactions with the electrolyte.

It is preferable that the specific surface area of this negative electrode active material is 0.5-6 m <2> / g. If the specific surface area is more than 6 m 2 / g, there is a risk of causing undesirable side reactions with the electrolyte, if less than 0.5 m 2 / g, the area in contact with the electrolyte is narrow, the charge and discharge reaction is not easy.

X-ray diffraction analysis showed that the (002) plane interlayer distance (d ₂ ) of the crystalline carbon particles in the active material was 3.35-3.4 Å, and the (002) plane interlayer distance (d ₂ ) of the amorphous carbon serving as a binder was 3.4-3.7 kPa.

The content of amorphous carbon in the active material according to the present invention is preferably 5-50% by weight of the total active material. If the content of amorphous carbon is less than 5% by weight, it is difficult to preferably improve the shape of the crystalline carbon, and if it is more than 50% by weight, the voltage flatness may be poor due to excessive amorphous carbon.

The prepared active material is a spherical active material, which can improve the packing density of the electrode plate, and induces random orientation of highly crystalline, highly oriented carbon particles during the pressing process of the electrode plate, thereby expanding the volume of the electrode plate in one direction during the insertion and removal of lithium ions. And shrinkage can be minimized. In addition, the microporous channel formed between the amorphous carbon-coated crystalline carbon primary particles facilitates the impregnation of the electrolyte during charge and discharge, thereby improving the high rate charge and discharge characteristics and the life characteristics of the battery.

Those skilled in the art can easily produce a lithium-based battery, such as a lithium ion battery, a lithium ion polymer battery, according to a known battery manufacturing method using the negative electrode active material of the present invention.

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are merely provided to more easily understand the present invention, and the present invention is not limited to the following examples.

Example 1

The coal-based pitch was treated with tetrahydrofuran to remove the tetrahydrofuran insoluble component and a tetrahydrofuran soluble pitch composed only of the soluble component was prepared. A solution prepared by dissolving a coal-based pitch in tetrahydrofuran (solid content 30%), that is, an amorphous carbon precursor solution was prepared. 300 g of plate-shaped artificial graphite having a particle diameter of about 5 μm was introduced into a powder granulator (Agglomaster AGM-2, Hosokawa Micron), and the hot air inlet temperature was set to 60 ° C., and a pulse jet dispersion was added. The fluidized bed was formed. As described above, 500 g of the amorphous carbon precursor solution prepared after drying the plate-shaped artificial graphite was sprayed and supplied to the plate-shaped artificial graphite powder flowing through the two-fluid nozzle at a rate of about 13 g / min. At this time, the weight ratio of plate-shaped artificial graphite and amorphous carbon precursor was 5: 2. Subsequently, the plate rotation speed was performed at 500 rpm to roll the plate-shaped artificial graphite particles coated with the amorphous carbon precursor solution on the rotating plate, whereby a plurality of these particles were collected and combined to form a secondary particle. The spherical material was dried and heat-treated at 1000 ° C. for 2 hours to prepare a battery active material.

A slurry was prepared by mixing the active material in a solution in which polyvinylidene fluoride was dissolved in N-methyl pyrrolidone as a binder. This slurry was cast on a copper foil current collector to prepare a negative electrode plate. A lithium secondary battery was prepared using this electrode plate as a working electrode, a lithium metal foil as a counter electrode, a mixture of ethylene carbonate and dimethyl carbonate in which 1M LiPF ₆ was dissolved as an electrolyte, and then tested for performance thereof. 1 is shown.

Example 2

It carried out similarly to Example 1 except having used natural graphite particle | grains whose particle diameter is about 18 micrometers instead of plate-shaped artificial graphite.

Example 3

The same procedure as in Example 1 was carried out except that a mixture of natural graphite particles having a particle diameter of about 18 μm and plate artificial graphite having a particle size of about 6 μm was used in a 4: 1 weight ratio instead of the plate-shaped artificial graphite.

Example 4

The same procedure as in Example 1 was performed except that a mixture of natural graphite particles having a particle size of about 18 μm and amorphous artificial graphite having a particle size of about 5 μm was used instead of plate-shaped artificial graphite in a 4: 1 weight ratio.

Example 5

The same procedure as in Example 1 was carried out except that a mixture of natural graphite particles having a particle size of about 18 μm and plate artificial graphite having a particle size of about 6 μm was used in a 3: 2 weight ratio instead of the plate-shaped artificial graphite.

Example 6

Instead of the plate-shaped artificial graphite, a mixture of natural graphite particles having a particle diameter of about 18 μm and plate-shaped artificial graphite having a particle diameter of about 6 μm in a 4: 1 weight ratio was used, and the weight ratio of the injected crystalline carbon particles and the amorphous carbon precursor was 5: 1. It carried out similarly to Example 1 except having set to.

Example 7

Example 6, except that a mixture of natural graphite particles having a particle diameter of about 18 μm and plate artificial graphite having a particle diameter of about 6 μm was used in a 4: 1 weight ratio instead of plate-shaped artificial graphite, and phenol resin was used instead of coal-based pitch. The same procedure was followed.

Example 8

Naphtha cracking heavy oil (PFO, Samsung General Chemical) was used instead of the coal-based pitch, and the same procedure as in Example 6 was carried out except that toluene was used instead of tetrahydrofuran as a solvent.

Comparative Example 1

A plate and a battery were manufactured using the same method as in Example 1 using plate-like artificial graphite powder as an active material.

Comparative Example 2

A pole plate and a battery were manufactured using the same method as in Example 1 using a lean piece natural graphite powder having a particle diameter of about 18 μm as an active material.

Comparative Example 3

A mixed solution of 100 g of a 3: 2 weight ratio mixture of natural graphite having a particle diameter of about 18 μm and plate-shaped artificial graphite having a particle size of about 6 μm, and 20 g of a phenol resin, an amorphous carbon precursor, dissolved in tetrahydrofuran (concentration: 20%) It was added to the mixture and refluxed and filtered. The obtained powder was carbonized at 1000 ° C. for 2 hours to obtain a carbon active material having a crystalline carbon core and an amorphous carbon shell. Using this active material, a plate and a battery were manufactured using the same method as in Example 1.

Active material Plate Average particle size (㎛) Specific surface area (㎡ / g) d ₂ (Å) Lc (Å) Plate density (g / ㏄) (pressure: 1 ton / ㎠) Example 1 20.1 1.9 3.368 905 1.7 Example 2 53.1 2.1 3.361 1598 1.6 Example 3 38.4 2.5 3.360 610 1.7 Example 4 47.8 2.7 3.364 690 1.6 Example 5 35.4 1.2 3.364 810 1.6 Example 6 27.8 3.7 3.361 1035 1.7 Example 7 54.2 6.7 3.361 715 1.6 Example 8 43.1 1.5 3.360 1010 1.5 Comparative Example 1 6.2 15.2 3.365 408 1.9 Comparative Example 2 18.2 12.1 3.356 2020 2.0 Comparative Example 3 19.2 5.3 3.357 2040 1.9 Battery characteristics Discharge capacity (h / g) efficiency(%) High rate characteristic (1C capacity) Life span characteristics (50 times,%) Example 1 345 89.1 340 92 Example 2 353 90.1 345 93 Example 3 352 90.6 340 92 Example 4 345 88.0 338 91 Example 5 351 91.4 345 93 Example 6 352 90.1 342 90 Example 7 355 86 348 91 Example 8 351 92 345 93 Comparative Example 1 340 80 270 85 Comparative Example 2 335 83 250 84 Comparative Example 3 320 87 295 86

As shown in Table 1, the active material of Example 1-8 has a specific surface area of about 1.5-6 m 2 / g, showing a smaller value as compared to Comparative Example 1-2 (12-15 m 2 / g), the particle diameter is 25㎛ or more As it represents a significantly larger value than Comparative Example 1-2, it can be estimated that the shape of the active material according to Example 1-8 is spherical. Looking at the electrode plate density after the pressing process, it can be seen that in Comparative Examples 1-3, the electrode plate density increased due to the perfect orientation of the highly crystalline active material particles, but this phenomenon did not appear in Example 1-8. .

It is understood that the active material of Example 3 shown in FIG. 2A is spherical, but the active material of Comparative Example 2 shown in FIG. 3A is lean. In addition, it can be seen that the electrode plate according to Example 3 of FIG. 2B and the electrode plate according to Comparative Example 2 of FIG. 3B exhibit significantly different surface states. As described above, the active material according to the embodiment is spherical, so the electrode plate has a high packing density, and unlike the active material according to the comparative example, which exhibits perfect orientation during the pressing process, high-rate charge and discharge characteristics and lifetime characteristics are induced by inducing random orientation of crystalline carbon particles. A good battery can be provided. As a proof, the results of Table 1 show that the battery of Example 1-8 shows superior high rate characteristics and lifespan characteristics compared to Comparative Example 1-2. In addition, the improved high rate charge and discharge characteristics and lifespan characteristics of the active material according to the present invention are considered to be attributable in part to the easy electrolyte impregnation by the microporous channel formed between the primary particles. Here, the life characteristics represent the capacity after 50 cycles of charge and discharge as a percentage of the initial capacity.

As shown in Table 1, it can be seen that Example 1-8, in which amorphous carbon is introduced between crystalline carbon particles, also has better charge and discharge efficiency than Comparative Example 1-2.

In addition, in the case of Comparative Example 3, the efficiency was improved by introduction of an amorphous coating, but it was impossible to improve the high-rate characteristics, and it can be seen that Examples 1-8 showed better charge and discharge characteristics than Comparative Example 3.

Differential thermal analysis (DTA) was performed to know the structures of the active materials prepared in Example 5, Comparative Example 2 and Comparative Example 3. The temperature range is 200-1000 ° C, the temperature increase rate is 10 ° C / min, and the results of differential thermal analysis in an air atmosphere show that in Example 5, one peak and 700 which are considered to be amorphous below 700 ° C at the boundary of 700 ° C It was confirmed that one of the peaks thought to be crystalline peaks above 占 폚 showed that the granulated-composite material was synthesized into a crystalline-amorphous composite structure. The differential thermal analysis results are shown in Table 2.

First peak position (° C.) 2nd peak position (° C) Number of peaks Example 5 674 790 2 Comparative Example 2 - 860 One Comparative Example 3 - 848 One

As shown in Table 2, it can be seen that there are two DTA exothermic peaks at 1000 ° C. or less in the negative electrode active material according to the present invention having excellent charge and discharge characteristics up to efficiency, high rate, and lifetime characteristics. This allows the amorphous carbon portion remaining after the carbonization process to maintain the random orientation of the lean flake or plate crystal carbon and enable the spherical active material shape. Accordingly, it can be seen that the active material having two peaks as amorphous and crystalline in the differential thermal analysis is an active material capable of maximizing the effect of the present invention.

Since the active material according to the present invention is spherical, the electrode plate density can be improved, and random orientation of highly crystalline high-orientation carbon particles is induced, thereby minimizing volume expansion and contraction in one direction of the electrode plate during charging and discharging, thereby improving battery life characteristics. do. In addition, by suppressing the perfect orientation of the amorphous or plate-like active material in the pressing step of the electrode plate, it is possible to prevent the sudden increase in the electrode plate density.

In addition, by coating crystalline carbon with an appropriate amount of amorphous carbon, it is excellent in voltage flatness, and by forming a microporous channel in the active material particles, it is easy to impregnate the electrolyte solution, thereby providing a battery having excellent high rate charge / discharge characteristics.

In addition, since the crystalline carbon particles, which cannot be used below the appropriate particle size, can be controlled to an appropriate particle size, the productivity can be increased and the cost of manufacturing the active material can be reduced.

Claims (14)

At least one crystalline carbon primary particle is coated with amorphous carbon, the primary particles coated with the amorphous carbon are assembled to form a substantially spherical secondary particles, lithium-based battery negative electrode active material. The negative active material of claim 1, wherein a microporos channel is formed between the primary particles coated with the amorphous carbon. The negative active material of claim 1, wherein the negative active material has two or more differential thermal analysis exothermic peaks at 1000 ° C. or less. The method of claim 1, wherein the shape of the crystalline carbon primary particles is amorphous, plate-like, lean piece, spherical, fibrous or a mixture thereof, the crystalline carbon primary particles are (002) plane interlayer distance during X-ray diffraction analysis (d ₂ ) is 3.35-3.4 Å and the amorphous carbon has a (002) plane interlayer distance (d ₂ ) of 3.4-3.7 Å in an X-ray diffraction analysis. The negative electrode active material of claim 1, wherein the negative electrode active material secondary particles have a particle size of 5-100 μm and a specific surface area of 0.5-6 m 2 / g. The negative active material of claim 1, wherein the average size of the crystalline carbon primary particles is 0.1-30 μm. The negative active material of claim 1, wherein the amorphous carbon content is 5-50% by weight of the total active material. Preparing an amorphous carbon precursor solution by dissolving, melting, softening or dispersing the amorphous carbon precursor in a solvent; Coating and granulating one or more crystalline carbon primary particles with the amorphous carbon precursor solution, and then spheroidizing to prepare secondary particles; And Method for producing a negative active material for a lithium-based battery comprising the step of carbonizing the spherical secondary particles. The method of claim 8, wherein the amorphous carbon precursor is selected from the group consisting of coal-based pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil and polymer resin. The method of claim 8, wherein the solvent is selected from the group consisting of toluene, tetrahydrofuran, benzene, methanol, ethanol, hexane, cyclohexane, and water. The method of claim 8, wherein the coating and granulation comprises mixing and agglomeration of the crystalline carbon primary particles into an amorphous carbon precursor solution, or spray drying or spraying an amorphous carbon precursor solution onto the crystalline carbon particles. A method for producing a negative electrode active material for a lithium-based battery, which is carried out by pyrolysis. The method of claim 8, wherein the carbonization process has a temperature of 700-1400 ° C. 10. The method of claim 8, further comprising a pulverization and / or classification step for screening the active material having a predetermined size or before the carbonization process. Dissolving, melting, softening or dispersing the amorphous carbon precursor in a solvent to prepare an amorphous carbon precursor solution; And A method of manufacturing a negative electrode active material for a lithium-based battery, comprising the steps of coating, granulating, and spheroidizing one or more crystalline carbon primary particles with the amorphous carbon precursor solution to produce secondary particles.