KR20180091331A - Manufacturing method of graphites for lithium-ion battery anode materials and Manufacturing Method lithium-ion battery electrode using graphites manufactured by the method - Google Patents

Abstract

Disclosed are a method for producing graphite for negative electrode materials in lithium ion batteries, and a method for producing an electrode for lithium ion batteries using graphite produced thereby. According to an embodiment of the present invention, the method for producing the graphite for negative electrode materials in lithium ion batteries comprises the following steps: (a) preparing a hydrogel solution; (b) mixing a carbon precursor with a hydrofluoric acid solution and applying ultrasonic waves to the mixture; (c) mixing and reacting the hydrogel solution prepared in the step (a) with the carbon precursor which has been reacted in the step (b); (d) carbonizing the mixture which had completed the reaction in the step (c); and (e) graphitizing the mixture carbonized in the step (d).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing graphite for a lithium ion battery anode material, and a method for manufacturing a lithium ion battery electrode using graphite produced by the method. }

The present invention relates to a process for producing graphite for a lithium ion battery anode material and a process for producing a lithium ion battery electrode using the graphite produced thereby. More particularly, the present invention relates to a process for producing lithium ion battery electrode, The present invention relates to a method for manufacturing a lithium ion battery electrode having excellent discharge efficiency by producing graphite for a battery cathode material.

Lithium-ion batteries (LIBs) have made it possible to use electric devices such as smart phones and notebooks that are simple and portable. Recently, LIBs are also used in electric vehicles (EV) and large scale energy storage systems (ESS).

Transition metal oxide (LiCoO ₂ , LiMnO ₄ ) is used as a cathode material in lithium ion battery, and graphite is mainly used as an anode material. Graphite is known to have high energy density, low voltage, and low hysteresis to voltage, and has been mainly used as an anode material. The charging and discharging of the lithium ion battery proceeds as the lithium ions in the positive electrode are inserted and desorbed between the graphite layers constituting the negative electrode.

On the other hand, the electrochemical performance of graphite used as an anode material of a lithium ion battery is affected by interfacial migration of lithium ions, diffusion coefficient and conductivity of the electrode. In particular, the electrochemical performance of graphite is strongly influenced by the chemical diffusion coefficient of lithium ions inserted between layers. This is because graphite has a disadvantage in that a narrow interlayer spacing and a diffusion distance of lithium ions are long due to insertion of lithium ions. Accordingly, when the charge / discharge rate of lithium ions is increased, a lithium dendrite is formed on the surface of graphite, so that the electrode capacity efficiency can be reduced.

In order to solve the above problem, the use of amorphous carbon instead of graphite, which is a crystalline carbon, has been proposed. The amorphous carbon has a wide interlayer spacing and micropores between the crystallites, which facilitates insertion and removal of lithium ions. However, amorphous carbon has a problem of large initial charge / discharge loss and severe deterioration.

On the other hand, the oxidation stabilization process is essential for the carbon material obtained from most carbon precursors in order to increase the carbon yield. The oxidation stabilization process prevents the carbon precursor from being melted by heat in a subsequent high temperature heat treatment process (carbonization, graphitization). However, this process requires a long reaction time and high cost.

Various oxidative stabilization processes have been proposed in order to solve the above problems. For example, US Pat. No. 4,031,118 uses oxidizing gas such as sulfuric acid and nitrogen oxide (NOx) to increase the stabilization speed, Open No. 10-2002-0058372 discloses a method of applying hot air while supplying air.

However, the above processes still have a long reaction time and a large cost.

It is an object of the present invention to provide a method for producing graphite for a lithium ion battery anode material without oxidation stabilization process which requires a long reaction time and a high cost.

It is still another object of the present invention to provide a method of manufacturing a lithium ion battery electrode having excellent discharge efficiency using graphite produced without an oxidation stabilization process.

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

According to an aspect of the present invention, there is provided a method of preparing a hydrogel, comprising: (a) preparing a hydrogel solution; (b) mixing a carbon precursor with a hydrofluoric acid solution and adding ultrasonic waves to the carbon precursor; (c) mixing and reacting the hydrogel solution prepared in the step (a) with the carbon precursor which has been reacted through the step (b); (d) carbonizing the reaction mixture through the step (c); And (e) graphitizing the carbonized mixture through the step (d). The present invention also provides a method for producing graphite for a lithium ion battery cathode material.

Between step (b) and step (c), the step (b) may further include pulverizing the carbon precursor that has been reacted.

Wherein the hydrogel solution comprises 10 to 35% by weight of a polymer precursor in the hydrogel solution, wherein the polymer precursor is selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polymethylmethacrylate (PMMA), polylactic acid (PLA), and acrylic acid (acylic acid, AAc), or a mixture thereof.

In the step (c), the carbon precursor may be mixed in an amount of 20 to 40 parts by weight based on 100 parts by weight of the hydrogel solution.

Further, in the step (c), a crosslinking agent and an initiator may be further mixed.

The crosslinking agent may be selected from glutaraldehyde (GA) and ethylene glycol demethacrylate. The crosslinking agent is preferably mixed with 1 to 10 parts by weight based on 100 parts by weight of the polymer precursor .

The initiator may be potassium persulfate, and the initiator is preferably mixed in an amount of 0.01 to 1 part by weight based on 100 parts by weight of the polymer precursor.

The carbonization step (d) may be performed at a temperature of 1,000 to 1,500 ° C for 0.5 to 2 hours, and the step (e) of graphitizing may be performed at a temperature of 2,500 to 3,000 ° C for 0.5 to 2 hours Lt; / RTI >

According to another aspect of the present invention, there is provided a method of manufacturing a lithium ion battery electrode, comprising the steps of: pulverizing graphite produced by the above manufacturing method; Dispersing the powdered graphite and the binder in a solvent to prepare a dispersion solution; Coating the dispersion solution on a copper (Cu) foil, and drying the dispersion solution.

According to the present invention as described above, it is possible to produce graphite optimized for a lithium ion battery cathode material while stabilizing it without a long reaction time and expensive oxidation stabilization process.

Also, the lithium ion battery electrode manufactured using the graphite obtained by the present invention has excellent discharge efficiency as compared with the conventional one.

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

1 is an SEM image of graphite produced through an embodiment of the present invention.
FIG. 2 is a graph showing a capacitance-voltage curve, a discharge efficiency, and a cycle characteristic according to a discharge current of a lithium ion battery manufactured using graphite according to an embodiment of the present invention.
FIG. 3 is a graph showing a capacitance-voltage curve, a discharge efficiency, and a cycle characteristic according to a discharge current of a lithium ion battery manufactured using graphite according to a comparative example of the present invention.
4 is a graph showing the single-particle diffusion coefficient of graphite and pure graphite according to an embodiment of the present invention.
FIG. 5 is a graph of capacitance-voltage curves, measured charge transfer resistances, and exchange currents according to charge / discharge and discharge currents using graphite particles according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. It is provided to inform.

A method for producing graphite for a lithium ion battery cathode material according to an embodiment of the present invention (hereinafter, referred to as a 'method for producing graphite') is stabilized without requiring oxidation stabilization, which is conventionally required, So that it can be manufactured.

Hereinafter, the present invention will be described in detail.

A method for producing graphite for a lithium ion battery cathode material according to an example of the present invention comprises the steps of: (a) preparing a hydrogel solution; (b) mixing a carbon precursor with a hydrofluoric acid solution and adding ultrasonic waves to the carbon precursor; (c) mixing and reacting the hydrogel solution prepared in the step (a) with the carbon precursor which has been reacted through the step (b); (d) carbonizing the reaction mixture through the step (c); And (e) graphitizing the carbonized mixture through the step (d).

First, the hydrogel solution includes a polymer precursor.

The polymer precursor may be any polymer capable of producing a hydrogel. Examples of the polymer precursor include polyvinyl alcohol (PVA), polyethylene oxide (PEO), polymethylmethacrylate, (PMMA), polylactic acid (PLA), and acrylic acid (acylic acid, AAc), or a mixture thereof.

It is preferable that the polymer precursor is mixed in the hydrogel solution in an amount of 10 to 35% by weight. When the mixing ratio of the polymer precursor is less than the lower limit, there is a fear that the viscosity of the hydrogel may not be maintained to maintain the shape of the hydrogel. When the upper limit is exceeded, the amount of the cross-linking agent and the initiator, which are adjusted to the polymer precursor relative to the hydrogel solution, decreases, and the reaction time and the reaction temperature increase. When the viscosity of the hydrogel solution is excessively high And the shape of the polymer is opaque, rather than the shape of the transparent gel, which is easy to absorb moisture.

Next, in step (b), a carbon precursor is mixed with a hydrofluoric acid solution and reacted by applying ultrasonic waves. In the present invention, the carbon precursor is reacted by adding ultrasonic waves in a hydrofluoric acid solution to introduce a fluorine functional group into the carbon precursor, and then hydrogel Solution. The reaction of the carbon precursor with hydrofluoric acid in the hydrofluoric acid solution is carried out in order to prepare graphite suitable for a lithium ion battery cathode material while stabilizing it without the oxidation stabilization process which is conventionally required. For example, the oxidation stabilization process, which has been required in the past, requires an air atmosphere, a temperature range of 300 to 400 ° C, and a reaction time of 2 to 5 hours, which consumes excessive energy and cost and has a problem of a long reaction time. However, according to the present invention, it is possible to achieve the effect of the conventional oxidation stabilization process by simply applying ultrasonic waves in the hydrofluoric acid solution for 10 to 40 minutes, thereby reducing the energy and cost and shortening the reaction time .

It is preferable that the ultrasound is added and reacted for 10 to 40 minutes after the carbon precursor is mixed with the hydrofluoric acid solution. If the reaction time is shorter than the lower limit, the carbon precursor may not be stabilized If the ultrasonic treatment time exceeds the upper limit value, the carbon precursor becomes perfluorinated, and the crystal structure of the graphite to be produced may collapse or thermal conductivity and compressive strength may be lowered, which is not preferable.

Next, in step (c), the hydrolyzed solution prepared in step (a) is mixed with the carbon precursor that has been reacted through step (b) and reacted.

The carbon precursor may be any graphitizable material such as isotropic pitch, anisotropic pitch, coal and phenol, or a mixture thereof, but is not limited thereto.

In this case, the carbon precursor is preferably powdered and mixed to uniformly distribute the carbon precursor over the entire area when the carbon precursor is gelled through the reaction of step (c). The step (b) may further include pulverizing the carbon precursor that has been reacted before the step (c). The degree of pulverization may be variously selected depending on the physical properties of the target graphite and the like.

In the step (c), it is preferable that the carbon precursor is mixed in an amount of 20 to 40 parts by weight based on 100 parts by weight of the hydrogel solution. When the mixing ratio of the carbon precursor is less than the lower limit, If the mixing ratio of the carbon precursor exceeds the upper limit value, the carbon precursor is not uniformly dispersed in the hydrogel solution, and the carbon precursor is aggregated or the carbon precursor is dispersed in the hydrogel solution There is a fear that the physical properties of graphite produced separately may not be uniform, which is not preferable.

Also, the reaction of step (c) is preferably carried out in a state where a crosslinking agent and an initiator are mixed, and the crosslinking agent and the initiator are added in order to efficiently crosslink the hydrogel solution in which the carbon precursor is evenly dispersed.

The crosslinking agent may be selected from, but not limited to, glutaraldehyde (GA) and ethylene glycol demethacrylate, and mixtures thereof. The cross-linking agent is preferably mixed in an amount of 1 to 10 parts by weight based on 100 parts by weight of the polymer precursor.

The initiator may be potassium persulfate, for example, and the initiator may be mixed in an amount of 0.01 to 1 part by weight based on 100 parts by weight of the polymer precursor.

If the mixing ratio of the cross-linking agent and the initiator is less than the lower limit value, gelation may not be sufficiently performed or the reaction time may become longer, which is not preferable. When the mixing ratio of the cross-linking agent and the initiator exceeds the upper limit The components of the crosslinking agent and the initiator may volatilize during the carbonization and graphitization process to be described later, which may cause excessive voids in the graphite, which is not preferable.

When the reaction of step (c) is completed, a gel in which the carbon precursor having the fluorine functional group introduced therein is uniformly dispersed over the entire area can be obtained. The conditions such as the reaction time and the reaction temperature in the step (c) can be appropriately adjusted depending on the size and mixing ratio of the carbon precursor added.

The gelled mixture through step (c) is made into graphite suitable for lithium ion battery cathode material through carbonization in step (d) and graphitization in step (e).

The carbonization in the step (d) is performed at a temperature of 1,000 ° C. to 1,500 ° C. In the course of this step, the polymer precursor, the carbon precursor having weak crystallinity, the crosslinking agent and the initiator are volatilized, and the gelled mixture is carbonized through the step (c). The carbonization step of step (d) is preferably performed in the temperature range of 0.5 to 2 hours.

When the temperature and time in the carbonization process are less than the lower limit, it is not preferable because the polymer precursor, the carbon precursor having weak crystallinity, the crosslinking agent and the initiator are not sufficiently volatilized and they may remain on the carbon. The temperature of carbon exceeds the upper limit value, the carbon crystallizes rapidly, which may result in an unstable form, which is not preferable. When the reaction time exceeds the upper limit value in the above temperature range, there is no difference from the effect at the upper limit value, and there is a possibility that only unnecessary energy is wasted, which is not preferable.

The carbonization process of the step (e) is performed at a temperature of 2,500 ° C to 3,000 ° C which is quite high, unlike the carbonization process of the step (d).

If the temperature and time in the graphitization process are less than the lower limit, there is a fear that the structure of the graphite to be produced, that is, the channel structure and the interlayer spacing, may be unstably formed. If the temperature and time exceed the upper limit There is no difference from the effect at the upper limit value and unnecessary energy is wasted, which is not preferable.

In the present invention, it is preferable that the carbonization process in the step (d) and the graphitization process in the step (e) are performed in an inert gas atmosphere. This is to minimize undesired side reactions. At this time, any of the inert gases known as nitrogen gas may be used for the carbonization process in the step (d), and argon gas is preferably used for the graphitization process in the step (e). This is because the graphitization process in the step (e) is performed at a high temperature of from 2,500 ° C. to 3,000 ° C. In this case, when nitrogen gas is used, decomposition of nitrogen gas occurs at a temperature of about 1,500 ° C. or more, And it is preferable to use argon gas which is stable even at a high temperature of 1,500 DEG C or more.

Also, the present invention provides a method of manufacturing a lithium ion battery electrode using graphite produced as described above. In the method of manufacturing a lithium ion battery electrode according to an example of the present invention, graphite produced by the above- ; Dispersing the powdered graphite and the binder in a solvent to prepare a dispersion solution; And coating the dispersion solution on a copper (Cu) foil and drying it.

The binder may be polyvinylidene fluoride (PVDF), and the binder may be added in a proportion of 5 to 15 parts by weight based on 100 parts by weight of the graphite.

Hereinafter, the present invention will be described in more detail with reference to Examples and Test Examples.

Example  : Manufacture of graphite after ultrasonic fluorination

6 g of polyvinyl alcohol as a polymer precursor and 14 g of acrylic acid were placed in 60 g of a 1 M NaOH aqueous solution and stirred for 10 minutes to prepare a hydrogel solution.

Next, 30 g of an anisotropic pitch (Mitsubishi gas chemical company, softening point (SP) 275-295 ° C.) was added to 100 mL of a hydrofluoric acid solution and reacted by ultrasonic wave (750 W, 20 kHz) for 30 minutes. Then, the anisotropic pitch, , Dried in an oven at 100 DEG C for 1 hour.

Then, 28 g of the dried anisotropic pitch was added to the hydrogel solution, 0.5 g of glutaraldehyde and 1 g of ethylene glycol dimethacrylate were mixed as a cross-linking agent, 0.01 g of potassium persulfate was mixed as an initiator, 87 x 61 x 57 mm) and stirred.

Next, the mixture was gelled at 60 DEG C for 3 hours and then dried at 100 DEG C for 1 hour.

Next, carbonization was carried out in a nitrogen gas atmosphere at 1,100 DEG C for 1.5 hours, and then graphitization was conducted at 2,700 DEG C for 1 hour in an argon gas atmosphere to prepare graphite for a lithium ion battery negative electrode material. Respectively.

Comparative Example  : Manufacture of Graphite through Conventional Oxidation Stabilization Process

Graphite was prepared using an anisotropic pitch obtained by oxidative stabilization at 300 DEG C for 4 hours in an air atmosphere instead of ultrasonic treatment in the hydrofluoric acid solution in the above example.

Surface shape

The surface morphology of the graphite prepared in Example 1 was photographed using a field-emission scanning electron microscope (FE-SEM, Hitachi, S-8230) and is shown in FIG.

Referring to the left image of FIG. 1, it can be seen that the size of the graphite particles is 8.79 ± 0.41 μm. The right image of FIG. 2 shows the enlarged surface of the graphite particles. It can be confirmed that a slit-structure, which is a characteristic of the graphite structure, is developed inside the graphite particle. Also, . These shapes and structures are thought to increase the diffusion distance and the migration path of lithium ions.

Elemental content

Elemental content of graphite and pure anisotropic pitch produced in Example 1 and Comparative Example 1 were analyzed using an X-ray photoelectron spectrometer (XPS, MultiLab 2000 spectrometer, Thermo Electron Corporation, UK) , And the obtained results are shown in the following table.

As can be seen from the above table, the graphite produced according to Example 1 of the present invention had oxygen element and fluorine element content of 19.88% and 21.18%, respectively, and the content of oxygen element was higher than graphite and anisotropic pitch according to Comparative Example 1 And the content of fluorine element which was not shown in graphite and anisotropic pitch according to Comparative Example 1 was as high as 21.18%.

This is because, in the case of the graphite according to Example 1 of the present invention, the anisotropic pitch is reacted with the hydrofluoric acid solution in the state of applying ultrasonic waves.

In general, fluorine functional groups are known to be hydrophobic and have low surface energy. However, when the oxygen element and the fluorine element are simultaneously introduced as described above, fluorine formed on the surface of the carbon precursor facilitates bonding of carbon and hydrogen, , And oxygen facilitates bonding with hydrogen. As a result, the bonding reaction between the carbon precursors is increased in the carbonization process, and thus it is possible to produce graphite for lithium ion batteries stabilized without the conventional oxidation stabilization reaction.

Specific surface area

The specific surface area of graphite produced by Example 1 and the specific surface area of pure anisotropic pitch were measured and are shown in the following table.

As can be seen from the above table, the specific surface area of the graphite prepared according to Example 1 of the present invention was about 10 times larger than that of the pure anisotropic pitch. This type of structure is considered to be very effective in reducing the diffusion length of lithium ions and increasing the migration path.

Thermal and mechanical properties

The thermal and mechanical properties of the graphite prepared in Example 1 and Comparative Example 1 were measured and are shown in the following table.

As can be seen from the above table, the graphite produced according to Example 1 of the present invention showed an increase in compressive strength and thermal conductivity by 39.18% and 19.51%, respectively, as compared with graphite produced by Comparative Example 1. [ That is, it was confirmed that the graphite produced according to Example 1 of the present invention had better compressive strength and thermal conductivity than the graphite produced by Comparative Example 1 which had undergone the conventional oxidation stabilization process.

Crystal Structure of Graphite Particles

The crystal structure of the graphite particles prepared in Example 1 and Comparative Example 1 was analyzed by X-ray diffraction (XRD, Bruker AXS, D8 DISCOVER) and the results are shown in the following table

As shown in the above table, the interlayer spacing in Example 1 and Comparative Example 1 was 3.380 Å and 3.384 Å, respectively, and the crystal thicknesses were 323.79 Å and 292.15 Å, respectively. That is, in the case of the graphite produced according to Example 1 of the present invention, the interlayer spacing decreased and the crystal thickness increased, indicating that the development of the crystal structure is easier.

Preparation of electrodes and evaluation of electrode characteristics

An electrode for a lithium ion battery was produced using the graphite produced in Example 1 and Comparative Example 1 of the present invention.

Specifically, the graphite produced in Example 1 was pulverized into particles having a size of 44 μm or less by using a ball mill, and powdered graphite (90 wt%) and binder PVDF (10 wt% dissolved in NMP, 10 wt% ) Was dispersed in 1-methyl-2-pyrrolidinone (NMP) as a solvent to prepare a slurry.

Next, the slurry was coated to a thickness of 21 mu m using a doctor blade on a copper (Cu) foil and dried to produce an electrode of a lithium ion battery.

Also, a lithium ion battery electrode was manufactured in the same manner as in Example 1 using the graphite produced in Comparative Example 1, and this was named as Comparative Example 1.

A lithium ion battery was manufactured using the electrode for the lithium ion battery, and the performance test was conducted.

(Diameter: 16 mm) of the lithium foil as a reference electrode, a polyolefin film having a nano-pore structure of poly (Ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3: 7) was used as the electrolyte and a 1M LIPF ₆ (ethylene carbonate And was prepared in the form of a coin-cell.

FIG. 2 is a graph showing a capacitance-voltage curve, discharge efficiency, and cycle characteristics of a lithium ion battery manufactured using the electrode of Example 1. FIG.

The capacitance-voltage curve according to the discharge current is shown on the upper left side of FIG. The discharge capacity of the electrode was measured at various discharging currents (0.5 - 30C) and repeatedly measured three times at 0.2C in order to measure the speed performance of the electrode for full charge. At this time, the discharge capacity was obtained from 0.2C to 369.91mAh / g, and the discharge efficiency according to the third repetition was 98%. After that, it was confirmed that the capacity at 30C was 345.3 mAh / g, and the discharge efficiency at this time was 98% (20C / 0.2C) and 92% (30C / 0.2C). The lifetime characteristics of the electrode are shown in the lower part of Fig. 2, and it was confirmed that the discharge capacity retention rate was maintained at 100% even after 50 cycles at 0.5C.

FIG. 3 is a graph showing a capacitance-voltage curve, discharge efficiency, and cycle characteristics of a lithium ion battery manufactured using the electrode of Comparative Example 1. FIG.

3, a capacitance-voltage curve according to a discharge current is shown on the upper left side. The discharge capacity of the electrode was measured at various discharging currents (0.5-20C) and repeatedly measured at 0.2C three times in order to measure the speed performance of the electrode for full charge. At this time, the discharge capacity was obtained from 0.2C to 321.43 mAh / g, and the discharge efficiency according to the third repetition was 98%. After that, it was confirmed that the capacity was 309.82 mAh / g at 20C, and the discharge efficiency at this time was 96% (20C / 0.2C).

From the above results, it can be concluded that the lithium ion battery using the electrode manufactured using the graphite manufactured according to the embodiment of the present invention has excellent discharge capacity, And the discharge efficiency was confirmed.

Single particle  Experiment

When the graphite prepared in Example 1 is used as an anode active material, a charge transfer reaction in which Li moves to the bulk from the surface and a single particle experiment to analyze the diffusion of the inserted lithium in the graphite material .

Unlike the conventional method, which is evaluated through the preparation of the mixed electrode, the particle test is performed by injecting only the active material into the beaker type cell together with the electrolyte (1M LiPF ₆ , EC: PC = 1: 1) The counter electrode is installed with a Li foil, and then the microelectrode coated with Cu is contacted with the graphite foam active material through an electron microscope equipped with a Manipulator connecting the microelectrode and charged and discharged with a current of nA in size, And diffusion within the active material. In this case, charging and discharging proceed only with the active material particles, and the applied current is a current of a few nA type. The overvoltage generated at this time is due to the charge transfer of Li ion on the surface and the overvoltage of Li ion migration in the active material Respectively. Therefore, the overvoltage was evaluated by charge transfer and diffusion coefficient inside the graphite according to the lithium content of graphite through tafel plot and GITT (Galvanostatic Intermittent Titration Technique).

The analysis of the charge transfer shows the overvoltage magnitude according to the applied current through the discharging of various currents to the fully charged particles, and the exchange current and the charge transfer resistance are obtained by the discharge states of each particle. The internal diffusion coefficient was evaluated by GITT. The applied current was advanced to 10 nA, the interval was 20, and the rest period was 3 minutes to obtain the OCV (open circuit voltage) of the material according to each charge state, and the results are shown in FIGS. 4 and 5 .

Figure 4 shows the diffusion coefficient of δLi _δ C ₆ in the open-circuit voltage (open circuit voltage, OCV) of the graphite and pure graphite (Hitachi chemical company, MAG, 8m 2 / g) produced according to the first embodiment of the present invention will be.

As can be seen from the figure, the graphite produced according to the embodiment of the present invention has a diffusion coefficient of 3.2 × 10 ^-12 to 2.0 × 10 ^-9 cm ² / s. That is, in the case of the graphite prepared in Example 1 of the present invention, the diffusion coefficient according to the charged state of the lithium ion was observed to be relatively stable as compared with pure graphite (Hitachi chemical company, MAG, 8 m ² / g) .

That is, the graphite according to Example 1 of the present invention is considered to be very easy to diffuse lithium ions according to the reduction of the diffusion distance of lithium ions and the increase of travel path. From this, graphite produced according to Example 1 of the present invention It can be explained that the electrode of the lithium ion battery manufactured by using has a high charge / discharge rate while having a high electrode capacity.

FIG. 5 shows the results of charging and discharging with the graphite single particles produced according to Example 1 of the present invention. (a) shows the result of 3 cycles at 10 nA current, and (b) shows the results of discharging experiments with various discharge currents from 10 nA to 1,000 nA with fully charged particles. The results show that the overvoltage according to the applied current for each lithium insertion state in graphite is plotted against the discharge displacement depth (DOD) through the tafel plot in (c) and (d) And the symmetry factor (f) of the speed determination step of the state. The size of the measured single particles was 23 탆 in diameter and charged and discharged at 10 nA, and a reversible capacity of 4.9 nAh was confirmed. The 10 nA applied current at this time is a current corresponding to 2 C when 10 nA is compared with the charging rate (C-rate) of the coin cell. The discharge capacity according to the applied discharge current in the fully charged state at 10 nA was measured to be 4.3 nAh at 1,000 nA discharge, which corresponds to 89% of the discharge capacity at 10 nA. That is, even at 200 C, it was confirmed that the amount corresponding to 89% of the fully charged particle capacity can be discharged. The symmetry factor (f) of this state and the exchange current and charge transfer resistance of this discharge state were calculated through the tafel plot of the same discharge voltage according to each applied current. The measured charge transfer resistance was 120 ~ 200 Ωcm 2 and the exchange current was 0.15 ~ 0.2 ㎃ / ㎠.

Although the present invention has been described with reference to the accompanying drawings and the preferred embodiments and test examples, the present invention is not limited thereto but is limited by the following claims. Accordingly, those skilled in the art will appreciate that various modifications and changes may be made thereto without departing from the spirit of the following claims.

Claims (11)

(a) preparing a hydrogel solution;
(b) mixing a carbon precursor with a hydrofluoric acid solution and adding ultrasonic waves to the carbon precursor;
(c) mixing and reacting the hydrogel solution prepared in the step (a) with the carbon precursor which has been reacted through the step (b);
(d) carbonizing the reaction mixture through the step (c); And
(e) graphitizing the carbonized mixture through the step (d). The method for producing graphite for a lithium ion battery anode material according to claim 1,
The method according to claim 1,
The method for producing graphite for a lithium ion battery negative electrode material according to claim 1, further comprising the step of pulverizing the carbon precursor having been reacted through the step (b) between the step (b) and the step (c)
The method according to claim 1,
Wherein the hydrogel solution comprises 10 to 35% by weight of the polymer precursor in the hydrogel solution,
The polymer precursor may be selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polymethylmethacrylate (PMMA), polylactic acid (PLA), and acylic acid ), And mixtures thereof. ≪ / RTI >
The method according to claim 1,
Wherein the carbon precursor is mixed in an amount of 20 to 40 parts by weight based on 100 parts by weight of the hydrogel solution in the step (c).
3. The method of claim 2,
Wherein the crosslinking agent and the initiator are further mixed in the step (c).
6. The method of claim 5,
The crosslinking agent is selected from glutaraldehyde (GA) and ethylene glycol demethacrylate, and the crosslinking agent is mixed with 1 to 10 parts by weight based on 100 parts by weight of the polymer precursor. Method for manufacturing graphite for ion battery negative electrode material.
6. The method of claim 5,
Wherein the initiator is potassium persulfate and 0.01 to 1 part by weight of the initiator is mixed with 100 parts by weight of the polymer precursor.
The method according to claim 1,
Wherein the carbonizing step (d) is performed at a temperature ranging from 1,000 to 1,500 ° C. for 0.5 to 2 hours.
The method according to claim 1,
Wherein the graphitizing step of step (e) is performed at a temperature ranging from 2,500 to 3,000 DEG C for 0.5 to 2 hours. The method for producing graphite for a lithium ion battery cathode material according to claim 1,
9. A process for producing graphite, comprising the steps of: powdering graphite produced by the process according to any one of claims 1 to 9;
Dispersing the powdered graphite and the binder in a solvent to prepare a dispersion solution;
Coating the dispersion solution on a copper (Cu) foil, and drying the dispersion solution.
11. The method of claim 10,
Wherein the binder is polyvinylidene fluoride (PVDF), and the binder is added in an amount of 5 to 15 parts by weight based on 100 parts by weight of the graphite.

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