KR102178565B1 - Anode Active Material for Lithium-Ion Secondary Battery - Google Patents

Abstract

The present invention relates to a new negative electrode active material for a lithium secondary battery, a negative electrode using the same, and a lithium secondary battery employing the same.

Description

Anode Active Material for Lithium-Ion Secondary Battery, Anode Active Material for Lithium-Ion Secondary Battery, Anode Active Material for Lithium-Ion Secondary Battery

The present invention relates to a new negative electrode active material for a lithium secondary battery, a negative electrode using the same, and a lithium secondary battery employing the same.

In general, amorphous carbon or crystalline carbon is used as an anode material of a lithium secondary battery, and crystalline carbon is mainly used because of its high capacity.

Such crystalline carbon includes natural graphite and artificial graphite.

In the case of artificial graphite, the charging and discharging efficiency is high, but the cost is high and the capacity is relatively low. In the case of natural graphite, since it is inexpensive and exhibits electrochemical properties similar to those of artificial graphite, it is highly useful as an anode active material.

However, since natural graphite has a plate shape, the surface area is large and the edge surface is exposed as it is, and when applied as a negative electrode active material, penetration or decomposition reaction of the electrolyte may occur.

For this reason, there is a problem in that the charging/discharging efficiency is low due to low initial efficiency and reversible capacity since the edge surface is peeled off or destroyed, causing a large irreversible reaction.

Therefore, in order to compensate for the problems of the conventional negative electrode material, amorphous carbon is coated on the electrode material particle surface.Since a mixture of various hydrocarbon compounds classified only as a softening point and quinoline insoluble matter is used, uniform coating is difficult and thus effective irreversible reaction is achieved. There is a disadvantage that it is difficult to lower it, and there is a need to develop an anode material that is an anode active material that can improve this.

The present invention is to solve the problem that charging and discharging efficiency is low due to low initial efficiency and reversible capacity due to large irreversible reaction due to peeling or destruction of an edge surface during use, since the conventional graphite active material is a plate shape.

In addition, the present invention is to provide a novel anode material capable of lowering a uniform coating and irreversible reaction, which was difficult to achieve, although a mixture of various hydrocarbon compounds was coated in order to compensate for the problem of the conventional anode material.

In addition, the present invention provides a negative electrode material, a new negative electrode active material capable of increasing initial efficiency and reversible capacity by improving coating uniformity to suppress the generation of a solid electrolyte interphase (SEI) layer.

In order to achieve the above object, the present invention

The present invention was achieved by providing a negative electrode active material prepared by mixing and firing a carbon coating agent and graphite satisfying the following conditions prepared by heat treatment from petroleum-based lower oil.

(1) Weight average molecular weight of 400 to 500 Daltons

(2) The content of the hydrocarbon compound containing 2 to 3 aromatic rings is 85 to 95% by weight based on the total carbon coating agent

(3) the fraction of hydrocarbon compounds containing 4 or more aromatic rings is 5% by weight or less, and

(4) 2% by weight or less of aliphatic hydrocarbon compounds

In addition, one aspect of the present invention is that the petroleum-based lower oil used to prepare the negative active material is FCC-DO (Fluid catalytic cracking decant oil), NCB (Naphtha-cracking bottom oil), EBO (Ethylene bottom oil), VR (Vacuum residue oil), heavy oil, super heavy oil, atmospheric residue oil and PFO (Pyrolized fuel oil) can be achieved by selecting one or more selected from.

Another aspect of the present invention is that the carbon coating agent is prepared by heat-treating the petroleum-based lower oil at 300 to 450°C for 10 minutes to 2 hours in an inert atmosphere, and then thermally polymerizing the petroleum-based lower oil for 1 hour to 10 hours at 300 to 400°C. A negative electrode coating agent having the above four characteristics can be prepared.

In addition, the present invention may be prepared by coating the negative electrode active material by mixing a carbon coating agent and graphite (graphite) in various aspects of the present invention, and thermally firing the negative electrode active material.

In addition, the present invention may further have a step of removing a hydrocarbon compound having a low boiling point that does not participate in the thermal polymerization reaction before the heat treatment.

In the present invention, after mixing the carbon coating agent and graphite, the coating may be coated while heating to 400 to 600° C. while stirring. The coating time is not particularly limited, but, for example, about 10 minutes to 10 hours is good.

In addition, in the present invention, the sintering may be performed at 800 to 1000° C. for 10 minutes to 10 hours without limitation after the coating.

In addition, in the present invention, in various aspects of the present invention, the negative electrode active material may be prepared by mixing 1 to 100 parts by weight of a carbon coating agent with respect to 100 parts by weight of graphite.

In addition, the present invention can provide a negative electrode for a lithium secondary battery manufactured by coating the negative electrode active material of the present invention of the various aspects on an electrode.

In addition, the present invention can provide a lithium secondary battery employing a negative electrode having the negative electrode active material.

According to the present invention, by coating the surface of a lithium secondary battery negative electrode material using a hydrocarbon compound mainly composed of an aromatic hydrocarbon compound having 2 to 3 aromatic rings produced from a petroleum-based low-grade material and a weight average molecular weight of 400 to 500 Da. As coating uniformity can be improved to suppress SEI layer formation, initial efficiency and reversible capacity can be increased.

In addition, since the conventional graphite active material is in a plate shape, the edge surface is peeled off or destroyed during use, resulting in a large irreversible reaction, thereby solving the problem of low charging/discharging efficiency due to low initial efficiency and reversible capacity.

In addition, the present invention can provide a novel anode material capable of lowering a uniform coating and irreversible reaction, which was difficult to achieve, although a mixture of various hydrocarbon compounds was coated to compensate for the problem of the conventional anode material.

Hereinafter, the present invention will be described in detail.

The present invention is FCC-DO (Fluid catalytic cracking decant oil), NCB (Naphtha-cracking bottom oil), EBO (Ethylene bottom oil), VR (Vacuum residue oil), heavy oil, ultra heavy oil, atmospheric residual oil and PFO (Pyrolized fuel) oil) using one or more petroleum-based lower oils to remove low-boiling hydrocarbon compounds, a pretreatment step of pyrolyzing the high molecular weight hydrocarbon compounds in the lower oil from which the low-boiling hydrocarbon compounds have been removed, and the pretreated hydrocarbon compounds To be prepared including the step of polymerizing,

The weight average molecular weight measured by MALDI_TOF is 400 to 500 Daltons,

85 to 95% by weight of a hydrocarbon compound having 2 to 3 aromatic groups,

The content of hydrocarbon compounds having 4 or more aromatic groups is 5% by weight or less, preferably 3% by weight or less, and

It relates to a mixture comprising a carbon coating agent having an aliphatic hydrocarbon compound of 2% by weight or less and graphite.

Therefore, if you look at the aspect of the present invention as an example, the following four conditions are satisfied by 2-dimensional gas chromatography (GC-2010Plus, Shimadzu) analysis and MALDI-TOF (Voyager-DE STR Biospectrometry workstation, Applied biosystems) analysis. It means a mixture of graphite and a carbon coating agent manufactured from petroleum-based lower oil.

(1) Weight average molecular weight of 400 to 500 Daltons

(2) The content of the hydrocarbon compound containing 2 to 3 aromatic rings is 85 to 95% by weight based on the total carbon coating agent

(3) the fraction of hydrocarbon compounds containing 4 or more aromatic rings is 5% by weight or less, and

(4) 2% by weight or less of aliphatic hydrocarbon compounds

In the above, the content of the hydrocarbon compound usually containing 4 or more aromatic rings may be 0.1 to 5% by weight, and the content of the aliphatic hydrocarbon compound may be 0.01 to 2% by weight.

In the present invention, when the content of the aromatic hydrocarbon compound having one aromatic ring is large or the weight average molecular weight is 400 Daltons or less, the residual amount is very low during heat treatment after coating on the surface of graphite (graphite), forming a very thin coating layer or partially coating. There is a problem, and if this is used, it is not good because the target effect in the present invention cannot be obtained or the effect is remarkably reduced.

In addition, when the content of aromatic hydrocarbon compounds containing 4 or more aromatic rings is high or the weight average molecular weight is 500 Daltons or more, the carbon coating agent does not have fluidity due to caulking during manufacture, or it has very low fluidity at high temperatures, so a uniform coating on the graphite surface is not possible. It is not good because it is not possible to obtain the desired effect in the present invention or the effect is remarkably reduced.

In addition, in the present invention, the negative electrode active material may be prepared by mixing and coating a carbon coating agent and graphite (graphite), followed by thermal firing.

In the present invention, after mixing the carbon coating agent and graphite, the coating may be coated while stirring while heating at 400 to 600°C, preferably 450 to 600°C, and the coating time is not particularly limited, but, for example, 10 minutes to 10 Time, preferably 2 to 8 hours is good.

In addition, in the present invention, the sintering may be performed at 800 to 1000° C. for 10 minutes to 10 hours without limitation after the coating.

In the present invention, the contents of the carbon coating agent and graphite are not particularly limited as long as the object of the present invention is achieved, but for example, 1 to 100 parts by weight of the carbon coating agent may be used based on 100 parts by weight of graphite.

In the present invention, the ratio is not necessarily observed, but when mixed within the above range, the carbon coating agent is sufficiently coated on the graphite particles, and the diffusion is sufficient when lithium ions are inserted and desorbed, thereby increasing the capacity.

Hereinafter, the method of manufacturing the carbon coating agent of the present invention will be described in more detail.

The manufacturing method of the carbon coating agent for a negative electrode material of a lithium secondary battery according to an exemplary embodiment of the present invention includes removing volatile components of hydrocarbon compounds having a low boiling point that do not participate in the thermal polymerization reaction in petroleum lower oil (heating or heating/vacuum removal or vacuum heating removal). It can be improved in various ways. For example, before the pretreatment step (first step heat treatment), the volatile components and low molecular weight compounds may be removed by heat treatment at a temperature above the boiling point, for example, 200°C for 1 hour.

In addition, in the present invention, it may be induced that the process of removing low-boiling volatiles and the process of cracking aliphatic chains occur simultaneously in the following pretreatment step (first stage heat treatment).

Subsequently, the present invention relates to the first step (pretreatment step) of cracking the aliphatic chain of the high molecular weight hydrocarbon compound remaining after the low boiling point material is removed, and the polymerization growth of the hydrocarbon compound to control the molecular weight and structure of the cracked material by the present invention. A second step (thermal polymerization step); And a third step of carbon coating graphite for a negative electrode material of a lithium secondary battery using the prepared carbon coating agent and heat treatment to prepare a negative electrode material for a lithium secondary battery.

Each condition is not particularly limited as long as it achieves the object of the present invention, but an example will be described as follows.

The pretreatment step of the present invention is a step of cracking a high molecular weight hydrocarbon compound and may mean heat-treating the petroleum-based lower oil at 300 to 450°C for 10 minutes to 2 hours in an inert atmosphere.

In addition, the polymerization step of increasing the molecular weight is prepared by thermal polymerization for 1 hour to 10 hours at 300 to 400°C, so that a negative electrode coating agent having the above four characteristics can be prepared.

On the other hand, the method of coating the carbon coating agent on graphite in the present invention is not particularly limited in a rotary kiln, etc., after mixing the carbon coating agent and graphite (graphite), but stirring at 10 to 400 rpm and 1 hour to 20 at 400 to 600 ℃ Time, preferably, can be coated while heating to 450 ~ 600 ℃, the coating time is not particularly limited, 10 minutes after 10 hours is good.

In addition, in the present invention, the sintering may be performed at 800 to 1000° C. for 10 minutes to 10 hours without limitation after the coating.

The finally prepared negative electrode active material powder may be classified using a sieve and used by adjusting an appropriate particle size if necessary. For example, although the average particle diameter may be classified into a particle diameter of 10 to 50 μm, it is not limited thereto.

If it is carried out at 450°C or higher in the pretreatment step of cranking, the content of the hydrocarbon compound having four or more aromatic rings increases due to minute coking, which is not preferable for the precursor of the carbon coating agent.

In the present invention, after coating the graphite with a carbon coating agent and firing, the obtained negative electrode active material powder was coated at 100 rpm for 5 hours in a rotary kiln at 500° C. for peeling. The coated graphite was heat-treated at a temperature of 900° C. for 2 hours and then classified through a 25 μm sieve to finally prepare a negative electrode material.

A negative electrode is prepared by a conventional method using the prepared negative electrode material, and a lithium secondary battery is manufactured using this to measure the characteristics of the present invention. When manufacturing the negative electrode in the present invention, other additives such as a current collector, a binder, and a thickener are not limited in the present invention.

Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. The embodiments of the present invention are examples for aiding understanding and are not limited to the embodiments of the present invention.

Example 1

[Manufacture of carbon coating agent]

PFO (Pyrolized fuel oil) as a raw material was treated at 400° C. for 1 hour in an inert gas (nitrogen) atmosphere to volatilize and remove low-boiling hydrocarbon compounds present in the raw materials, and at the same time crack high molecular weight aliphatic hydrocarbon compounds. Subsequently, polymerization was performed by heat treatment for an additional 4 hours at 350°C in an inert atmosphere. The average molecular weight of the prepared carbon coating agent was measured through MALDI-TOF analysis, and the composition ratio according to the structure was measured through 2D-GC analysis, and Table 1 shows the measurement results.

[Manufacture of cathode materials; Manufacture of carbon coated graphite]

The prepared carbon coating agent and graphite particles were mixed in a weight ratio of 1:2, and coated at 100 rpm for 5 hours at 500°C in a rotary kiln. The coated graphite was heat-treated at 900° C. for 2 hours and then classified through a 25 μm sieve to finally prepare a negative electrode material.

[Manufacture of coin-type lithium secondary battery]

The prepared negative electrode material, binder (styrene-butadiene rubber), and thickener (CMC) were mixed in a weight ratio of 90:6:4 and then dispersed in distilled water to prepare a negative electrode material slurry composition. The composition was coated on a copper foil current collector, dried and rolled to prepare an electrode density of 1.50±0.05 g/cm ³ . Using the negative electrode as a working electrode and lithium metal as a counter electrode, a 2032 coin-type half battery was fabricated. At this time, a separator made of a porous polypropylene film is inserted between the working electrode and the counter electrode, and as an electrolyte, a mixture of diethyl carbonate (DEC) and ethylene carbonate (EC) is 1:1 in a mixed solution having a concentration of 1M. What dissolved LiPF ₆ was used. As a result of evaluating the battery characteristics using the prepared battery, it is described as shown in Table 2.

Comparative Example 1

The experiment was performed using only the same graphite as in Example 1 without using a carbon coating agent.

Comparative Examples 2 to 4

Except for the heat treatment step of polymerization in Example 1, the same was carried out, and the analysis results according to the pretreatment conditions are listed in Table 1, and in the case of Comparative Examples 2 to 4, the 100 ^th cycle discharge capacity (mAh/g) is 220 or less. As was very inferior, it was found that it was significantly lowered even compared to 1 in comparison.

Comparative Examples 5 to 9

It was carried out in the same manner as in Example 1, except that the coating composition having the molecular weight and the fraction of the compound of Table 1 was used under the same conditions as in Table 1, and the results are listed in Table 2.

Examples 2 and 3

Except for the conditions in Table 1, it was carried out in the same manner as in Example 1. The results are listed in Table 2.

Pretreatment temperature
(Step 1; ℃) Polymerization temperature
(Step 2; ℃) Weight average
Molecular Weight
(Da) Containing n aromatic rings
Hydrocarbon compound content ratio (% by weight) Aliphatic
Hydrocarbon compounds n=1 n=2 n=3 n≥4 Comparative Example 2 350 0 191 5.2 43.8 42.3 8.7 0.0 Comparative Example 3 400 0 199 3.6 49.6 38.4 8.0 0.4 Comparative Example 4 450 0 232 0.9 38.9 41.6 14.2 4.4 Comparative Example 5 350 300 312 4.3 40.3 42.2 13.2 0.0 Comparative Example 6 350 350 374 3.7 34.2 40.4 20.8 0.9 Comparative Example 7 350 400 403 2.8 28.2 41.2 27.6 0.2 Comparative Example 8 400 300 398 1.4 26.4 45.6 26.6 0.0 Comparative Example 9 400 450 498 0.8 3.1 36.2 42.5 17.4 Example 1 400 350 427 1.1 8.4 47.6 42.6 0.3 Example 2 370 360 403 1.5 12.4 49.6 36.3 0.2 Example 3 400 400 459 0.5 4.2 48.2 46.0 1.1

1 ^st cycle
Charging capacity
(mAh/g) 1 ^st cycle
Discharge capacity
(mAh/g) 100 ^th cycle discharge capacity
(mAh/g) 1 ^st cycle
Coulomb efficiency (%) Retention (%) Comparative Example 1 388.4 332.8 286.4 85.7 86.1 Comparative Example 5 381.4 337.2 306.7 88.4 91.0 Comparative Example 6 379.8 334.8 311.2 88.2 93.0 Comparative Example 7 382.2 334.2 288.7 87.4 86.4 Comparative Example 8 372.6 331.4 299.8 88.9 90.5 Comparative Example 9 384.4 335.8 296.1 87.4 88.2 Example 1 366.4 348.6 339.8 95.1 97.5 Example 2 362.4 354.2 348.2 97.7 98.3 Example 3 361.8 356.4 352.5 98.5 98.9

As seen in Table 2 above, when the carbon coating agent satisfies the conditions of the present invention as in the present invention, it has a remarkable increase effect in the discharge capacity, and has a value of 90% or more, preferably 95% or more, which is excellent in the Coulomb effect. , The absolute value of the discharge capacity after 100 cycles is very large and excellent, and its retention rate (retention(%) = (B/A) × 100, A: discharge capacity after one cycle, B: discharge capacity after 100 cycles) 95 It can be seen that it has a significant increase of more than %, preferably more than 97%.

Claims (8)

It is a negative electrode active material produced by baking after coating a carbon coating agent produced by heat treatment of petroleum-based low-grade oil on plate-shaped graphite,
The carbon coating agent is a carbon coating agent satisfying the following (1) to (4),
An anode active material prepared by mixing 1 to 100 parts by weight of a carbon coating agent with respect to 100 parts by weight of the graphite.

(1) Weight average molecular weight 400 to 500 Daltons
(2) The content of the hydrocarbon compound containing 2 to 3 aromatic rings is 85 to 95% by weight based on the total carbon coating agent
(3) the fraction of hydrocarbon compounds containing 4 or more aromatic rings is 5% by weight or less, and
(4) 2% by weight or less of aliphatic hydrocarbon compounds
The method of claim 1,
The petroleum-based low-grade oil is FCC-DO (Fluid catalytic cracking decant oil), NCB (Naphtha-cracking bottom oil), EBO (Ethylene bottom oil), VR (Vacuum residue oil), heavy oil, ultra heavy oil, atmospheric residual oil and PFO (Pyrolized fuel oil) is one or more selected from the anode active material.
The method of claim 2,
The carbon coating agent is prepared by increasing the molecular weight by heat-treating the petroleum-based lower oil at 300 to 450°C for 10 minutes to 2 hours in an inert atmosphere, and then thermally polymerizing at 300 to 400°C for 1 hour to 10 hours .
The method of claim 3,
The negative electrode active material further comprising the step of removing the hydrocarbon compound having a low boiling point that does not participate in the thermal polymerization reaction before the heat treatment.
The method of claim 1,
The coating is performed for 10 minutes to 10 hours while stirring at 400 to 600 °C, and the sintering is performed at 800 to 1000 °C for 10 minutes to 10 hours.
delete A negative electrode for a lithium secondary battery prepared including the negative active material of any one of claims 1 to 5
A lithium secondary battery adopting the negative electrode of claim 7.