JP2003346796A - Compound carbon material and lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a raw material for an amorphous carbon material which is improved in formation efficiency of the amorphous carbon material and can be manufactured efficiently and simply in the compound carbon material in which the surface of a graphite material is coated by an amorphous carbon material and its manufacturing method, and a lithium ion secondary battery which uses this compound carbon material as a negative electrode material and has little gas generation. <P>SOLUTION: This is a compound carbon material in which the surface of a graphite material is coated by an amorphous carbon material. The amorphous carbon is made by making a naphthalene compound containing two or more of oxygen (O) or hydroxyl group (OH), at least one selected from anthracene compounds, and further, a material containing as necessary tar or pitch into carbide and is manufactured by a first heating process in which heating is carried out at 500°C as the upper limit and a second heating process in which heating is carried out in the inert gas atmosphere at 1000-1500°C as the upper limit. And a lithium ion secondary battery that uses this compound carbon material as a negative electrode is provided. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite carbon material, and more particularly, to a composite carbon material in which the surface of a graphite material is coated with an amorphous carbon material.

[0002]

2. Description of the Related Art Carbon materials used as negative electrode materials for lithium ion secondary batteries can be broadly classified into amorphous carbon materials and graphite materials.

[0003] When an amorphous carbon material is applied, the reaction with the electrolytic solution is small and the generation of decomposition gas is small. On the other hand, lithium ions are trapped in voids called micropores in the crystal structure and deactivated. There is a disadvantage that the repetition characteristics of charge and discharge are greatly reduced.

On the other hand, when a graphite material is used, although good repetition characteristics can be obtained as compared with amorphous carbon because there is no micropore, it reacts with the electrolytic solution to decompose the electrolytic solution to generate gas. It has the disadvantage of being easy.

In recent years, in order to solve these problems, attention has been paid to a composite carbon material having a multilayer structure of an amorphous carbon material and a graphite material having high crystallinity disclosed in Japanese Patent Application Laid-Open No. 4-370662. I have. Also, Japanese Patent Application Laid-Open No. 10-3027
Japanese Patent Application Publication No. 75-3750 discloses a method of treating a surface of a graphite material with a silane coupling agent to increase the bonding force with an amorphous carbon material. Is coated with a carbon material having a lower crystallinity than the carbon material.

[0006] Also, as to the raw materials (organic substances before firing) of the amorphous carbon material, there are disclosed a coal tar pitch disclosed in JP-A-6-84516, and JP-A-10-1498.
JP-A-2001-229917 discloses a reaction product obtained by reacting one kind of condensed polycyclic compound disclosed in JP-A No. 30 with a nitrogen-containing, sulfur-containing or oxygen-containing compound, and a thermoplastic resin disclosed in JP-A-2001-229917. There are aliphatic hydrocarbons, aromatic hydrocarbons and alicyclic hydrocarbons disclosed in JP-A-2000-264614.

[0007] By heating these organic substances in an atmosphere of an oxidizing gas or an inert gas, an amorphous carbon material is produced. Japanese Patent Application Laid-Open No. 4-368778 discloses a chemical vapor deposition method (CVD) using a hydrocarbon gas as a method for producing an amorphous carbon material in a gas phase.

[0008]

The composite carbon material has a feature that the generation of decomposition gas can be suppressed without lowering the battery performance of the lithium ion secondary battery. However, in order to form amorphous carbon on the surface of a graphite material, it is necessary to heat-treat an organic material, which is a raw material of the amorphous carbon material, under various conditions. Nevertheless, there is a problem that it is very difficult to efficiently form an amorphous carbon material.

[0009] In particular, price competition has become more severe due to the recent economic downturn, and the composite carbon material used for the negative electrode material of the lithium ion secondary battery not only contributes to the improvement of battery performance but also of low cost. There has been a demand for a simple manufacturing method that leads to the development of a device.

An object of the present invention is to improve the formation efficiency of an amorphous carbon material, and to provide a raw material, a production method of an amorphous carbon material, and a gas using a composite carbon material as a negative electrode material which can be produced with high efficiency and easily. An object of the present invention is to provide a lithium-ion secondary battery that generates less energy.

[0011]

Means for Solving the Problems In order to efficiently form an amorphous carbon material on the surface of a graphite material in a composite carbon material, the present inventor has set forth a starting material for the amorphous carbon material and heating conditions. After diligently studying the above, the present invention has been achieved.

That is, the present invention relates to a composite carbon material in which the surface of a graphite material is coated with an amorphous carbon material, wherein the amorphous carbon material is composed of oxygen (O) or hydroxyl (O).
H) wherein at least one selected from a naphthalene compound or an anthracene compound containing two or more H) is used as a raw material.

Here, the graphite material is generally called graphite, and any of these shapes, such as spheres, plates and fibers, can be used irrespective of natural or artificial properties.

Further, as naphthalene compounds and anthracene compounds containing at least two oxygen (O),
Naphthoquinone compounds, anthraquinone compounds and some of these compounds are converted to hydroxyl (OH), carboxyl (CO
OH) and a compound substituted with an amino group (NH ₂ ).

On the other hand, naphthalene compounds and anthracene compounds containing at least two or more hydroxyl groups (OH) include naphthalene diol, naphthalene triol, anthracentriol, anthracene tetrol, and a part of these compounds having a carboxyl group (COOH) or an amino group. (NH ₂ ) and the like.

Further, by adding tar or pitch as a component of inexpensive heavy oil or heavy coal to the raw material of the amorphous carbon material, the amorphous carbon material can be obtained at low cost. it can.

In order to coat the surface of a graphite material with an amorphous carbon material using a naphthalene compound or an anthracene compound as a raw material, a predetermined amount of the graphite material and the raw material of the amorphous carbon material are mixed and then heat-treated. good.

In order to obtain an amorphous carbon material efficiently, the first
The step includes a first heating step of holding at a constant temperature between a melting point and a boiling point of a naphthalene compound or an anthracene compound, which is a raw material of an amorphous carbon material, for at least one hour, and then performing heating up to 500 ° C. as an upper limit. . Then, as a second step, there is a second heating step of heating in an inert gas atmosphere with an upper limit of 1000 to 1500 ° C.

Here, the first heating step is performed for the purpose of generating a carbon precursor of an amorphous carbon material, and can be applied to both an active gas atmosphere and an inert gas atmosphere. From the viewpoint of the production efficiency of the carbon precursor, a dry air atmosphere is preferable.

On the other hand, in the second heating step, a helium gas atmosphere or a nitrogen gas atmosphere is preferable because the yield of the amorphous carbon material is reduced in an active gas atmosphere.
As the temperature exceeds ℃, crystallization of the amorphous carbon material proceeds.

The composite carbon material produced in this manner is applied to a positive electrode, a negative electrode and a negative electrode of a lithium ion secondary battery having a basic structure of an electrolytic solution. A secondary battery can be provided.

Here, the composite carbon material is P1 showing a peak in the range of 1550 to 1590 cm ^-1 in laser Raman using an argon laser (wavelength 514.5 nm) as excitation light, and 1330 to ¹ in similar laser Raman.
It has P2 showing a peak in the range of 380 cm ^-1 , and P1 and P
It is preferable that the intensity ratio (P2 / P1) R value with respect to R2 be in the range of 0.2 to 0.5.

The laser Raman spectrum peak P1 in the range of 1550 to 1590 cm ^-1 is based on the crystallinity of the graphite material, and the peak position slightly varies depending on the crystallinity.

The spectrum peak P2 in the range of 1330 to 1380 cm ^-1 is based on the irregular stacking of the carbon surface in amorphous carbon.

In laser Raman, since the physical properties of the surface of the composite carbon material are reflected, a large R value means that
It means that the amount of amorphous carbon on the surface is large. R value is 0.
If it is less than 2, the effect of suppressing the generation of decomposed gas due to the reaction with the electrolytic solution is weak, and if it exceeds 0.5, the battery performance deteriorates.

A method for producing the negative electrode is a known method, that is, a method in which a coating material in which a composite carbon material is dispersed in a binder resin solution is prepared, and the coating material is applied on a current collector and dried.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have reported that as a raw material of an amorphous carbon material coated on the surface, aromatic hydrocarbons such as naphthalene and anthracene, aliphatic hydrocarbons, alicyclic hydrocarbons, From 600 to 2
The present invention has been achieved based on a method of firing at 000 ° C.

Based on these facts, the inventors studied in detail a compound capable of obtaining amorphous carbon with high efficiency and heating conditions, and reached the present invention.

For example, when naphthalene and anthracene are mixed with graphite (weight ratio 1: 1) and heated to 400 ° C. in an air atmosphere as a first heating step, naphthalene and anthracene are completely burned off, and the residue is removed. Only graphite.

Similarly, when the air atmosphere is an inert gas and a helium gas atmosphere is used, only graphite is obtained as a residue.

However, compounds containing at least two oxygen (O) or hydroxyl groups (OH) as substituents in these naphthalenes and anthracenes can be obtained by heating up to 500 ° C. regardless of the gas atmosphere in the first heating step. It has been found that there is a feature that carbide can be obtained.

The reason why the naphthalene compound or anthracene compound containing at least two oxygen (O) or hydroxyl groups (OH) as the raw material of the amorphous carbon material in the present invention can obtain amorphous carbon with high efficiency is clear. However, these compounds themselves are capable of obtaining carbides with high efficiency in the first heating step, and are liquefied by being mixed with graphite and maintained at a temperature between the melting point and the boiling point for 1 hour or more. It is presumed that the contact area with graphite is increased to promote the chemical bonding force with graphite, and that the carbonization can be achieved with high efficiency because the evaporation of the compound itself is suppressed due to its boiling point or lower. .

By promoting the chemical bonding force, these naphthalene compounds and anthracene compounds have a sandwich structure sandwiched between graphite materials, the adhesion to the graphite materials is strengthened, and they are not easily burned out during the heating step. I guess.

By applying the composite carbon material thus produced to a negative electrode of a lithium ion secondary battery,
The amorphous carbon material formed on the surface of the graphite material suppresses decomposition of the electrolytic solution, and can provide a lithium ion secondary battery that generates less gas.

The present invention relates to a raw material for an amorphous carbon material, a production method, and a lithium ion secondary battery using the composite carbon material. It is possible to reduce the cost of the steps of manufacturing the negative electrode material for a secondary battery and the amorphous carbon material.

For practical use, generally, when an organic substance is heated in the air, the organic substance is destroyed by burning through a decomposition gas, but a part can be recovered as a carbonized substance depending on the heating conditions.

Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 5 parts by weight of graphite powder and 5 parts by weight of 2-hydroxy-p-naphthoquinone were mixed in a coffee mill, and the mixture was placed in a crucible container and heated from room temperature to 1000 in an electric furnace in a helium gas atmosphere. A heat treatment (temperature rise: 2 ° C./min) was performed.

(Comparative Example 1) As a comparative example, a heat treatment was carried out in exactly the same manner except that 2-hydroxy-p-naphthoquinone was changed to naphthalene.

The content of the amorphous carbon material when each compound was used was determined from the weight after the heat treatment. As a result, the content of 2-hydroxy-p-naphthoquinone was 1 wt%, and that of naphthalene was 0 wt%. Was.

[0041] Further, the sample after the heat treatment, the result was observed with a laser Raman device, R value obtained from the peak P2 and having a range of peak P1,1330～1380cm ^-1 with a range of 1550~1590cm ^-1 (P2 / P1)
Is 0.1 in the case of 2-hydroxy-p-naphthoquinone.
8. The case of naphthalene is 0.1 which is the same as the case of graphite alone.
It was 5.

In the case of 2-hydroxy-p-naphthoquinone, the R value was increased, and it was confirmed that an amorphous carbon material was formed on the surface of graphite.

However, in the case of naphthalene, it was determined from the results of the content of the amorphous carbon material and the R value that the surface of the graphite material was not coated with the amorphous carbon material in the present production method.

According to this embodiment, by using a specific naphthoquinone compound as a raw material of an amorphous carbon material, a simple method of performing high-temperature treatment in a helium gas atmosphere can be used.
The surface of the graphite material can be coated with an amorphous carbon material.

Example 2 After 5 parts by weight of graphite powder and 3 parts by weight of 2-hydroxy-p-naphthoquinone were mixed in a coffee mill, this mixture and 2 parts by weight of coal tar pitch were mixed at 160 ° C. for 30 minutes. Then, the mixture was placed in a crucible container and subjected to the same heat treatment as in Example 1 to produce a composite carbon material. The content of the amorphous carbon material in the composite carbon material is 0.5.
8 wt%, R value was 0.17.

According to this embodiment, there is an effect that the amorphous carbon material can be coated at low cost by using inexpensive coal tar pitch.

Examples 3 to 6 The 2-hydroxy-p-naphthoquinone used in Example 1 was replaced with 1,4,9,10-anthracecentetrol (melting point: about 150 ° C., boiling point: about 25
0 ° C.) and the mixing ratio (weight ratio) with graphite was changed to 4/6 in the same manner as in Example 1 except that graphite and 1,4,4 were used.
Mixture of 9,10-anthracentetrol (weight ratio 4
/ 6) were produced.

Next, as a first heating step, the mixture was heated from room temperature to 160 ° C. (2 ° C./min) in an electric furnace in a dry air atmosphere, and maintained at 160 ° C. for 0 hour and 1 hour, respectively. The heat treatment was performed for 3 hours, 3 hours, and 6 hours, and thereafter, heat treatment was performed up to 400 ° C.

Further, as a second heating step, a heating treatment from room temperature to 1000 ° C. in an electric furnace in a helium gas atmosphere (heating:
2 ° C./min) to produce a composite carbon material.

Table 1 shows the results of determining the content and R value of the amorphous carbon material in these composite carbon materials.

[0051]

[Table 1]

According to this embodiment, in the first heating step, the temperature (160) between the melting point and the boiling point of 1,4,9,10-anthracecentetrol, which is the raw material of the amorphous carbon material, is used.
C.) for at least one hour can increase the efficiency with which the amorphous carbon material is formed on the surface of the graphite material.

(Comparative Example 2) In Example 4, 1, 4,
The same procedure as in Example 4 was carried out except that 9,10-anthracene tetrol was changed to anthracene (melting point: about 217 ° C, boiling point: about 315 ° C), and the one-hour holding temperature in the first heating step was changed to 230 ° C. And the second heating step.

When the weight of the sample and the laser Raman after completion of the second heating step were measured, the content of the amorphous carbon material was 0%.
wt%, R value was 0.15, and no amorphous carbon material was formed on the surface of graphite.

Example 7 2 parts by weight of graphite material, 1,4,4
After mixing 1.5 parts by weight of 9,10-anthracecentol in a coffee mill, adding 1.5 parts by weight of coal tar pitch to the mixture and mixing at 160 ° C. for 1 hour, the same heating step as in Example 4 was performed. A composite carbon material was produced. The content of the amorphous carbon material in the composite carbon material was 3 wt%, and the R value was 0.28.

According to the present embodiment, the use of inexpensive coal tar pitch has the effect that the amorphous carbon material can be efficiently coated at low cost.

Example 8 A coating liquid was prepared by mixing 18 parts by weight of a composite carbon material prepared in the same manner as in Example 1 and 20 parts by weight of a 10 wt% polyvinylidene fluoride / N-methylpyrrolidone solution. A 20 μm thick copper foil was applied using an applicator and dried at 80 ° C. for 1 hour to prepare a negative electrode for a lithium secondary battery.

Next, LiPF ₆ (solvent: ethylene carbonate / ethyl methyl carbonate = 1/2 (volume ratio)) at a concentration of 1 mol / liter was placed in the glass cell, and the previously prepared negative electrode and an electrode having lithium metal as the positive electrode were prepared. Install
The battery was charged to 0 V with a constant current of 0.5 mA / cm ² , and
The battery was discharged to 1.5 V at a constant current of 5 mA / cm ² .

At this time, the charge capacity is 349 mAh / g, the discharge capacity is 321 mAh / g, and the efficiency is 92%.

Further, in order to measure the state of decomposition gas generation with the electrolytic solution, a 15φ negative electrode in which the above electrolytic solution was impregnated into a SUS coin cell with a gas collection pipe, and a 15
Using lithium of the positive electrode as a positive electrode, the battery was charged to 0 V at a constant current of 0.5 mA / cm ² , and the decomposition gas generated during this time was led to a mass spectrometer via a gas collection pipe for quantitative analysis.

When the decomposition gas generation state was evaluated for the hydrogen gas which generated the largest amount, the maximum value of the detection current, which is an index indicating the gas generation amount, was as low as 6.2 × 10 ^-11 A. As compared with the case where the surface was not coated with the amorphous carbon material ((Comparative Example 3)), generation of the decomposition gas could be reduced without substantially changing the charge / discharge characteristics.

According to this embodiment, by applying a composite carbon material using a specific naphthoquinone compound as a raw material of an amorphous carbon material to a negative electrode for a lithium ion secondary battery, the charge / discharge characteristics are not reduced. This has the effect of reducing the generation of decomposition gas.

Comparative Example 3 The charge / discharge characteristics and decomposition gas generation state were measured in the same manner as in Example 8 except that the composite carbon material of Example 8 was replaced with the graphite material of Comparative Example 1.

As a result, the charging / discharging characteristics showed a charging capacity of 347 m.
Ah / g, discharge capacity 315 mAh / g, efficiency 91%, the maximum value of the hydrogen gas detection current is 1 × 10 ⁻¹⁰ A, and the generation amount of the decomposition gas is smaller than when the composite carbon material is used as the negative electrode. There were many results.

(Examples 9 to 12) Using the composite carbon material prepared in Examples 3 to 6 as a negative electrode material, the charge / discharge characteristics and decomposition gas generation state were examined in the same manner as in Example 8. Table 2 shows the results.

[0066]

[Table 2]

As the R value of the composite carbon material increases, the discharge capacity slightly decreases, and the efficiency tends to decrease accordingly.

On the other hand, the amount of generated H ₂ gas tends to decrease as the R value increases. The R value is preferably in the range of 0.2 to 0.5 from the relationship between the charge / discharge characteristics and the amount of generated H ₂ gas.

According to the present embodiment, by setting the R value in the range of 0.2 to 0.5, the generation of the decomposition gas of the lithium ion secondary battery can be performed without deteriorating the charge / discharge characteristics of the graphite material. This has the effect of reducing

Example 13 Using the composite carbon material prepared in Example 7 as a negative electrode material, the charge / discharge characteristics and decomposition gas generation state were examined in the same manner as in Example 8. As a result, a charge capacity of 350 mAh / g, a discharge capacity of 311 mAh / g, an efficiency of 89%, and a maximum current value of H ₂ gas of 5.0 × 10 ⁻¹¹ A were obtained.

According to the present embodiment, by applying the inexpensive combined carbon material combined with coal tar pitch to the negative electrode material, generation of decomposition gas can be reduced without particularly deteriorating the charge / discharge characteristics. There is an effect that a costly lithium ion secondary battery can be obtained.

As described above, in the composite carbon material in which the surface of the graphite material is coated with the amorphous carbon material, the specific naphthalene compound and the anthracene compound are used as the raw materials of the amorphous carbon material, and the melting point and boiling point of the raw materials are used. It is manufactured from a first heating step of heating at 500 ° C. as an upper limit after holding at a temperature between 1 hour or more, and a second heating step of heating at 1000 to 1500 ° C. in an inert gas atmosphere. Thus, the efficiency of forming the amorphous carbon material on the surface of the graphite material can be increased, and the generation of decomposition gas can be reduced without lowering the charge / discharge characteristics.

[0073]

According to the present invention, the raw material of the amorphous carbon material, the production method, or the gas using the composite carbon material as the negative electrode material can be formed with high efficiency and improved efficiency by improving the formation efficiency of the amorphous carbon material. A lithium ion secondary battery with less generation can be provided.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Juichi Arai             Hitachi, Ibaraki Pref.             Hitachi, Ltd., Hitachi Laboratory (72) Inventor Shuichi Wada             1-88 Usutora, Ibaraki-shi, Osaka             Kusel Corporation F-term (reference) 4G146 AA19 AC16A AC16B AC23A                       AC23B AD02 AD15 AD25                       BA02 BA11 BA22 BA24 BC02                       BC23 BC32A BC32B BC33A                       BC33B BC34A BC34B BC37A                       BC37B                 5H029 AJ02 AJ14 AK11 AL06 AL07                       AL18 AM05 AM07 CJ02 CJ08                       CJ21 DJ16 EJ04 EJ11 HJ13                       HJ14                 5H050 AA02 AA15 AA19 BA17 CA17                       CB07 CB08 EA02 EA11 EA22                       EA24 FA17 FA18 FA20 GA02                       GA10 GA22 GA27 HA00 HA13                       HA14 HA20

Claims (6)

[Claims] 1. A composite carbon material in which the surface of a graphite material is coated with an amorphous carbon material, wherein the amorphous carbon material is oxygen (O) or a hydroxyl group (O
A composite carbon material characterized by being a carbonized material obtained from at least one selected from naphthalene compounds and anthracene compounds containing two or more H). 2. The composite carbon material according to claim 1, wherein the raw material of the amorphous carbon material contains tar or pitch. 3. A composite in which the surface of a graphite material is coated with an amorphous carbon material made from at least one selected from naphthalene compounds and anthracene compounds containing two or more oxygen (O) or hydroxyl groups (OH). In the method for producing a carbonized material, after maintaining the mixture of the graphite material and the raw material of the amorphous carbon material in a temperature range between the melting point and the boiling point of the naphthalene compound or the anthracene compound for 1 hour or more,
A method for producing a composite carbon material, comprising: a first heating step of heating at an upper limit of 00 ° C., and a second heating step of heating at an upper limit of 1000 to 1500 ° C. in an inert gas atmosphere. 4. The method according to claim 3, wherein the raw material of the amorphous carbon material contains tar or pitch. 5. A lithium ion secondary battery having a positive electrode, a negative electrode and an electrolytic solution, wherein the negative electrode comprises a graphite material having a surface formed of a naphthalene compound or an anthracene compound containing two or more oxygen (O) or hydroxyl groups (OH). A lithium ion secondary battery comprising a composite carbon material coated with an amorphous carbon material using at least one selected material as a raw material. 6. The composite carbon material is 1550 to 159.
Each scope and 1330～1380Cm ^-1 of 0 cm ^-1 showed a peak (P1 and P2) in laser Raman,
The intensity ratio (P2 / P1) R value of these peaks is 0.2 to 0.2.
2. The composite carbon material according to claim 1, wherein the range is 0.5.