KR20210043860A - Manufacturing method of graphite for Lithium ion battery anode with improved stability by introduction of semi-covalent C-F functional group - Google Patents

Abstract

The present invention relates to a method for manufacturing graphite for a negative electrode of a lithium ion battery with increased stability by introduction of a semi-covalent carbon-fluorine functional group. More specifically, the present invention relates to the method for manufacturing graphite for a negative electrode of a lithium ion battery, in which a semi-covalent carbon-fluorine functional group can be introduced by emitting graphite with an electron beam to increase active sites on the surface thereof and reacting the graphite with a low concentration of fluorine gas. In addition, the present invention provides the method for manufacturing graphite for a negative electrode of a lithium ion battery, in which the content of semi-covalent carbon-fluorine functional groups is increased so that a lithium fluoride film is mainly formed after initial charging, thereby increasing cycle stability of the lithium ion battery. According to the present invention, the method comprises a step of preparing surface-activated graphite particles and a step of introducing a semi-covalent carbon-fluorine group into the graphite particles.

Description

{Manufacturing method of graphite for Lithium ion battery anode with improved stability by introduction of semi-covalent C-F functional group}

The present invention relates to a method of manufacturing graphite for a lithium ion battery negative electrode material with improved stability by introducing a semi-covalent carbon-fluorine functional group.

More specifically, it relates to a method for producing graphite for a lithium ion battery negative electrode material capable of introducing a semi-covalent carbon-fluorine functional group by irradiating the graphite with an electron beam to increase the active site on the surface and then reacting with a low concentration of fluorine gas.

In addition, the present invention provides a method of manufacturing graphite for a lithium ion battery negative electrode material, which increases the content of the semi-covalent carbon-fluorine functional group to form a lithium fluoride film mainly after initial charging, thereby improving the cycle stability of a lithium secondary battery. will be.

In the lithium secondary battery, charging and discharging proceeds by repeating the process of intercalating and desorbing lithium ions from the lithium-based metal oxide as a cathode material between the layers of graphite as the anode material.

During charging and discharging, the electrolyte reacts with graphite, which is a negative electrode material, to form a thin film called SEI (Solid Electrolyte Interface, hereinafter SEI) on the graphite surface. It prevents the reaction of and acts as an ion channel through which only lithium ions pass between the electrolyte and the cathode.

The SEI film is composed of a combination of several components, but lithium fluoride (LiF) has the advantage of having a high capacity retention rate even after several tens of charge/discharge cycles because lithium fluoride (LiF) has high stability compared to other components. Accordingly, among methods for forming a graphite surface lithium fluoride film for an anode material, there is a method of inducing formation of lithium fluoride during charging and discharging using fluorine gas.

At this time, it is known that the semicovalent fluorine-carbon functional group has a major effect on the formation of lithium fluoride, and the covalent fluorine-carbon functional group has no significant effect.

Korean Patent Registration No. 10-1976252 (2019.04.30)

The present invention has been devised to solve the above-described problems, and an object thereof is to provide a method of manufacturing graphite for a lithium ion battery negative electrode material having a high content of semi-covalent carbon-fluorine functional groups by a simple process.

In addition, the introduced semi-covalent carbon-fluorine functional group mainly forms a lithium fluoride film on the surface of the negative electrode material after initial charging to provide graphite for a lithium ion battery negative electrode material that can improve the stability of a lithium secondary battery.

The object of the present invention is not limited to the above, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

An aspect of the present invention is a step of preparing surface activated graphite particles by irradiating electron beams to graphite particles,

Reacting the activated graphite particles with fluorine gas to introduce a semicovalent carbon-fluorine tube condenser to the graphite particles,

It provides a method of manufacturing a negative electrode material comprising a.

In one aspect of the present invention, the step of introducing the functional group may be prepared by reacting with fluorine gas in an inert atmosphere.

In one aspect of the present invention, the electron beam irradiation may be irradiated once or twice or more repeatedly.

In one aspect of the present invention, the electron beam may be irradiated at a rate of 10 to 100 kGy per irradiation, and a total electron beam absorption amount may be 30 to 800 kGy.

In one aspect of the present invention, the step of introducing the functional group may be performed in an inert atmosphere of low concentration fluorine gas.

In one aspect of the present invention, the low concentration fluorine gas may have a partial pressure of 0.05 to 0.25 bar.

Another aspect of the present invention is (1) the amount of fluorine element introduced into the graphite surface is 8 to 13%,

(2) the proportion of semi-covalent carbon-fluorine functional groups among the carbon-fluorine functional groups introduced into the graphite surface is 40% or more,

(3) It provides a negative electrode material for a secondary battery having a semi-covalent carbon-fluorine functional group having a content of 6 to 13% of the semicovalent carbon-fluorine functional group introduced into the graphite surface.

In one aspect of the present invention, the ratio of the semicovalent and covalent carbon-fluorine functional groups to the whole of the semicovalent and covalent carbon-fluorine functional groups may be 80% or more.

In one aspect of the present invention, the negative electrode material may have a capacity retention rate of 90% or more of a coin-type lithium-ion battery in which the cut-off voltage is fixed from 0.005 to 2.5 V, and charging and discharging are performed 100 times at a rate of 0.2 C. .

Another aspect of the present invention provides a lithium secondary battery employing the negative electrode material according to the above aspect.

In the case of the present invention, by introducing an electron beam irradiation step to increase the surface active portion of the graphite powder, and then by adopting a step of reacting with insoluble gas, semi-covalent carbon introduced from the reaction with a conventional low concentration fluorine gas- It is possible to obtain an effect of introducing a higher content than the fluorine functional group content.

In addition, according to the present invention, a lithium fluoride layer is formed on the surface of the graphite for an anode material at an early stage during initial charging, thereby having more excellent stability of a lithium ion battery.

According to the present invention, the active site is increased by irradiating the graphite with electron beams, reacting with a low concentration of fluorine gas to introduce a semi-covalent carbon-fluorine functional group to the surface, so that the amount of fluorine element introduced to the graphite surface is 9 to 13%. And, among the carbon-fluorine functional groups, the ratio of the semicovalent carbon-fluorine functional groups introduced to the graphite surface may be 85% or more, and the content of the semicovalent carbon-fluorine functional groups introduced to the graphite surface is 8 to 13%. Reuse graphite can be provided.

The effects of the present invention are not limited to those described above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

Hereinafter, the present invention will be described in more detail through specific examples or examples including the accompanying drawings. However, the following specific examples or examples are only one reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

In addition, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. The terms used in the description in the present invention are merely for effectively describing specific embodiments and are not intended to limit the present invention.

In addition, the singular form used in the specification and the appended claims may be intended to include the plural form unless otherwise indicated in the context.

In addition, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

The present invention provides a method of manufacturing graphite for a lithium ion battery negative electrode material with improved stability by introducing a semi-covalent carbon-fluorine functional group.

The method for producing graphite for a lithium ion battery negative electrode material according to the present invention,

A first step of increasing the surface active portion by irradiating the graphite particles with electron beams;

A second step of mainly introducing a semicovalent carbon-fluorine functional group by reacting a low-concentration fluorine gas with the graphite having an increased surface active site;

It provides a method for producing graphite particles of a negative electrode material comprising a.

In the graphite powder according to the present invention, the amount of fluorine element introduced into the graphite surface may be 9 to 13%, and the ratio of the semicovalent carbon-fluorine functional group among the carbon-fluorine functional groups introduced to the graphite surface may be 85% or more, It relates to graphite for a lithium ion battery negative electrode material in which the content of semi-covalent carbon-fluorine functional groups introduced into the graphite surface is 8 to 13%.

The graphite particles used for the anode material of the lithium ion battery used as the raw material of the present invention are not particularly limited as long as it is graphite that can be used for secondary batteries, and examples include, but are not limited to, natural graphite, artificial graphite, spheroidal graphite, plate shape. It may be selected from the group consisting of graphite and mixtures thereof. However, it is preferable to use spherical artificial graphite with relatively easy introduction of functional groups and excellent stability, but is not limited thereto.

Next, a method for modifying the surface of graphite particles as the negative electrode active material as the raw material will be described.

First, the electron beam irradiation step, which is the first step of the present invention, is a step of increasing the surface active site by irradiating an electron beam to a conventional graphite granule. Increasing the activation site by irradiation with the former is not obvious, but by this irradiation step, the incorporation of fluorine introduced at the later stage is smooth, and the amount of the semicovalent carbon-fluorine functional group is increased. That is, this step is performed to increase the surface active site in order to more effectively introduce the semicovalent carbon-fluorine functional group to the graphite surface in a later step.

The electron beam irradiation of the present invention may be carried out at room temperature and in an air atmosphere, and the electron beam irradiation increases an activation site by irradiating an electron beam once or two or more times using an electron beam accelerator. The electron dose is not particularly limited as long as it achieves the object of the present invention, but for example, it may be irradiated at 10 to 100 kGy per irradiation using an electron beam accelerator, and for example, the total electron beam absorption amount is 30 To 800 kGy, preferably 50 to 500 kGy, but is not limited thereto. In the above range, the active site generating radicals on the surface can be sufficiently secured, and a sufficient amount of introduction of the semicovalent carbon-fluorine functional group can be secured in the reaction with fluorine gas, which is a subsequent step, so it is preferred, but is not limited thereto. .

Graphite having an increased surface active site through the first step as described above reacts with a low concentration of fluorine gas in the second step to introduce a fluorine functional group to the surface thereof, and in particular, a semi-covalent carbon-fluorine functional group is mainly introduced.

As the fluorinated raw material used in the reaction step of introducing the fluorine gas, fluorine value is preferred, but alternatively, it can be introduced from various materials containing fluorine, for example, fluorine compounds such as boron trifluoride or nitrogen trifluoride. And a mixture thereof or a mixture of these and fluorine gas, and the like may be used.

The fluorine gas reaction step of the present invention may be performed in an inert gas atmosphere or in an air atmosphere containing oxygen, but as far as side reactions are suppressed, it is more preferable to perform the reaction in a non-percent atmosphere. That is, the process of introducing the fluorine functional group in the second step is more preferably performed after repeating the process of injecting and evacuating an inert gas several times in order to minimize unwanted side reactions.

The process of introducing the semicovalent carbon-fluorine functional group in the second step is more preferably carried out at room temperature and pressure, but the reaction is not limited because it can be carried out at both a temperature above room temperature and a pressure above atmospheric pressure.

More preferably, the process of introducing the semi-covalent carbon-fluorine functional group in the second step is preferably performed using a mixed gas of fluorine gas and inert gas, and the amount of fluorine gas introduced is limited as long as fluorine gas is introduced. Although it is not necessary, for example, it is more preferable to carry out under low concentration fluorine gas conditions in which the partial pressure of the insoluble gas is 0.05 to 0.25 bar, since it is reproducible and can further increase the selectivity of the semicovalent carbon-fluorine functional group. That is, when the partial pressure of the fluorine gas in the mixed gas used in the second step is at a low concentration, the introduction amount of the semi-covalent carbon-fluorine functional group is further increased, and the reaction occurs instantaneously by adjusting the content of the highly reactive fluorine gas to a low concentration. It is preferred because it prevents the content of the covalent carbon-fluorine functional group from increasing on the surface of the graphite, but is not necessarily limited to the low concentration of the present invention.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the following Examples and Comparative Examples are only one example for describing the present invention in more detail, and the present invention is not limited by the following Examples and Comparative Examples.

[Example 1]

Preparation of graphite for negative electrode material of lithium-ion battery with semi-covalent carbon-fluorine functional group introduced

After placing graphite powder (average particle diameter of 20 µm) in a glass dish, an electron beam of 50 kGy was irradiated four times using an electron beam accelerator so that the total electron beam absorption amount was 200 kGy, thereby increasing the surface active area of graphite.

Thereafter, the graphite with the increased surface active area was added to the reactor, and the inside of the reactor was vacuumed, and then a mixed gas of argon gas with a partial pressure of 0.2 bar of fluorine gas was added so that the inside of the reactor became atmospheric pressure, and graphite for 10 minutes Reacted with the graphite to introduce a semicovalent carbon-fluorine functional group to the graphite.

Functional group analysis

To analyze the functional groups of the prepared surface-modified graphite, that is, to analyze the content of the semicovalent carbon-fluorine functional group, XPS (X-ray Photoelectron Spectroscopy, Thermo Fisher Scientific Co., VG Multilab 2000) analysis was performed. In addition, the ratios of carbon, oxygen, and fluorine elements on the graphite surface are shown in Tables 1 and 2 below from the ratio of the integral values of the 1s area of carbon (C), 1s area of oxygen (O), and 1s area of fluorine (F).

Coin-type lithium-ion battery manufacturing

The prepared graphite for a lithium ion battery negative electrode material was mixed with a binder (polyvinylidene fluoride) in a weight ratio of 9:1 and then dispersed in N-methylpyrrolidone to prepare a slurry for a lithium ion battery negative electrode material. The prepared slurry was coated on a copper foil current collector, dried and rolled to obtain an electrode density of 1.60±0.05 g/cm ³ . The negative electrode is used as a working electrode and lithium metal is used as a counter electrode, and a separator made of a porous polypropylene film is inserted between the working electrode and the counter electrode, and the mixing volume ratio of diethyl carbonate (DEC) and ethylene carbonate (EC) is A 2032 coin-type lithium ion battery was prepared by adding an electrolyte solution in which 1M concentration of LiPF _{6 was dissolved in a 1:1 mixed solution.}

Coin-type lithium-ion battery electrochemical characteristics evaluation

The manufactured coin-type lithium-ion battery fixed the cut-off voltage from 0.005 to 2.5 V, and performed charging and discharging up to 100 times at a rate of 0.2. The retention rate at the time is shown in Table 3.

[Example 2]

In Example 1, except that the partial pressure of the fluorine gas was 0.04 bar, it was carried out in the same manner. The results are shown in Tables 1 to 3.

[Example 3]

In Example 1, except that the partial pressure of the fluorine gas was 0.3 bar, it was carried out in the same manner. The results are shown in Tables 1 to 3.

[Comparative Example 1]

Except for the process of performing electron beam irradiation in Example 1, the procedure of Example 1 was carried out in the same manner as in Example 1, except that a carbon-fluorine functional group was introduced at a partial pressure of 0.2 bar of fluorine gas. The results are shown in Tables 1 to 3.

[Comparative Example 2]

In Comparative Example 1, it was carried out in the same manner as in Comparative Example 1, except that the partial pressure of the fluorine gas was 0.04 bar. The results are shown in Tables 1 to 3.

[Comparative Example 3]

Comparative Example 1 was carried out in the same manner as in Comparative Example 1 except that the partial pressure of the fluorine gas was 0.3 bar. The results are shown in Tables 1 to 3.

[Comparative Example 4]

It was carried out in the same manner as in Example 1, except that the graphite of Example 1 itself was used, which did not go through the first and second steps. The results are listed in Tables 1 to 3.

XPS elemental analysis data division Elemental Content (At.%) C1s F1s O1s Example 1 88.1 11.2 0.7 Example 2 91.3 7.8 0.9 Example 3 82.4 17.1 0.5 Comparative Example 1 91.9 7.4 0.7 Comparative Example 2 94 5.2 0.8 Comparative Example 3 86.4 13.2 0.4 Comparative Example 4 98.8 0 1.2

Comparison of semi-covalent carbon-fluorine and covalent carbon-fluorine ratio and content division
Existence ratio according to the type of carbon-fluorine functional group (%) Content according to the type of carbon-fluorine functional group (%) Anti-common Commonality Anti-common Commonality Example 1 91.5 8.5 10.2 1.0 Example 2 83.6 16.4 6.5 1.3 Example 3 48.6 51.4 8.3 8.8 Comparative Example 1 72.6 27.4 5.4 2.0 Comparative Example 2 64.8 35.2 3.4 1.8 Comparative Example 3 35.1 64.9 4.6 8.6 Comparative Example 4 - - - -

As can be seen from the results of Table 1 and Table 2 above, the examples in which the reaction with fluorine gas was reacted after the first stage electron beam irradiation increased the introduction of carbon-fluorine functional groups compared to Comparative Examples 1 to 3 without the electron beam irradiation step under the same conditions, In addition, it can be seen that the selectivity of the semicovalent carbon-fluorine functional group is remarkably high.

That is, in order to find out the detailed bonding type of the carbon-fluorine functional group introduced on the graphite surface, the S orbital of the fluorine atom was separated and analyzed (deconvolution) to calculate the abundance ratio according to the type of carbon-fluorine functional group. It can be seen that the examples of the present invention are remarkably improved in the formation selectivity and introduction ratio of the fluorine functional group.

In addition, as shown in Table 3 below, the capacity retention rate after 100 cycles of the lithium ion battery made from pure graphite was 88.1% as shown in Comparative Example 4, and in the case of the example of the present invention, the electron beam irradiation of Example 1 The case showed a capacity retention rate of 98.1%, and had a capacity retention rate that was significantly increased compared to 94.6%, which was the case of Comparative Example 1 reacted with fluorine gas without electron beam irradiation under the same conditions, and compared to Example 2 in Table 3 below. In Example 2 or Example 3 and Comparative Example 3, the same tendency showed remarkable improvement in electrical properties.

Electrical characteristics comparison division Discharge capacity (mAh/g) Capacity retention rate after 100 times (%) 1 cycle 100 cycle Example 1 368.4 361.4 98.1 Example 2 366.2 351.2 95.9 Example 3 368.8 339.7 92.1 Comparative Example 1 365.4 345.5 94.6 Comparative Example 2 367.2 332.6 90.6 Comparative Example 3 367.8 331.4 90.1 Comparative Example 4 368.2 324.3 88.1

As described above, in the present invention, it has been described by specific matters and limited embodiments and drawings, but this is only provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and the present invention is Those of ordinary skill in the relevant field can make various modifications and variations from these descriptions.

Therefore, the spirit of the present invention is limited to the described embodiments and should not be defined, and all things that are equivalent or equivalent to the claims as well as the claims to be described later fall within the scope of the spirit of the present invention. .

Claims (11)

Producing surface-activated graphite particles by irradiating the graphite particles with electron beams,
Reacting the activated graphite particles with fluorine gas to introduce a semicovalent carbon-fluorine tube condenser to the graphite particles,
Method for producing a negative electrode material comprising a. The method of claim 1,
The step of introducing the functional group is a method for producing a negative electrode material by reacting with fluorine gas in an inert atmosphere. The method of claim 1,
The electron beam irradiation is a method of manufacturing a negative electrode material that is irradiated once or twice or more. The method of claim 3,
The electron beam may be irradiated at a rate of 10 to 100 kGy per irradiation, and a method of manufacturing a negative electrode material having a total electron beam absorption of 30 to 800 kGy. The method of claim 1,
The step of introducing the functional group is a method for producing a negative electrode material to be performed in an inert atmosphere of low concentration fluorine gas. The method of claim 5,
The low-concentration fluorine gas is a method for producing a negative electrode material having a partial pressure of 0.05 to 0.25 bar. (1) the amount of fluorine element introduced into the graphite surface is 8 to 13%,
(2) the proportion of the semicovalent carbon-fluorine functional groups introduced into the graphite surface among the carbon-fluorine functional groups is 40% or more,
(3) A negative electrode material for secondary batteries having a semi-covalent carbon-fluorine functional group having a semicovalent carbon-fluorine functional group having a content of 6 to 13% introduced into the graphite surface. The method of claim 7,
A negative electrode material for a secondary battery in which a ratio of the semicovalent and covalent carbon-fluorine functional groups to the whole of the semicovalent and covalent carbon-fluorine functional groups is 80% or more introduced to the graphite surface. The method according to any one selected from claim 7 or 8,
The negative electrode material is a secondary battery negative electrode material having a capacity retention rate of 90% or more of a coin-type lithium-ion battery in which a cut-off voltage is fixed from 0.005 to 2.5 V and charging and discharging at a rate of 0.2 C is performed up to 100 times. A lithium secondary battery employing the negative electrode material according to any one of claims 7 or 8. A lithium secondary battery adopting the negative electrode material of claim 9.