JP3526645B2 - Method for producing multi-phase structured carbon electrode material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode material suitable for a non-aqueous solvent secondary battery, and more particularly to a method for producing a carbon electrode material having a multiphase structure.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of electronic equipment, a high capacity secondary battery has become necessary. In particular, lithium secondary batteries, which have higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries, have been receiving attention. Attempts were initially made to use lithium metal as the negative electrode material, but lithium was deposited in a dendritic form (dendritic form) during repeated charging and discharging, penetrated the separator, and reached the positive electrode, and short-circuited both electrodes. It turned out that there is a possibility that it will end up. Therefore, attention has been paid to carbon-based materials that can prevent dendrites instead of metal electrodes.

As a carbon-based secondary battery electrode material, it has been considered to use a carbonaceous material having a multiphase structure as disclosed in Japanese Patent Application Laid-Open No. 4-171677. This is due to the advantages (high capacity and small irreversible capacity) of carbonaceous matter with high crystallinity, the disadvantages (decomposing the propylene carbonate-based electrolyte solution) and the advantages of carbonaceous material with low crystallinity (stability with the electrolyte solution). The idea is to combine the advantages and disadvantages (small capacity and large irreversible capacity), while making the most of each other's strengths while compensating for their weaknesses.

[0004]

However, when the carbon-based electrode material is used in a cylindrical battery, it is usually necessary to make the carbon-based electrode material into a powder form in order to form the electrode into a sheet shape. Even in the case of the carbonaceous material having a multiphase structure described in JP-A-4-171677, there is a problem that the coating is broken and the core is exposed because the carbonaceous material has a multiphase structure, and the electrode performance is deteriorated. . The present invention provides a method for continuously firing a carbonaceous material having a multiphase structure, which is obtained by coating a carbonaceous material having a high crystallinity with a carbonaceous material having a relatively low crystallinity, with high quality. .

[0005]

According to the present invention, a powdery raw material obtained by coating a carbonaceous material having a high degree of crystallinity with a carbonaceous material containing a condensed polycyclic hydrocarbon compound as a main component and heat-treating A carbon electrode material having a multi-phase structure is obtained by carbonizing a phase of a carbonaceous material of a surface layer by firing at 700 to 1800 ° C. in an inert gas while giving rotary motion by a rotary kiln without sintering. It is a method of manufacturing a carbon electrode material for a secondary battery.

A carbonaceous material having a high degree of crystallinity, which finally forms nuclei in a secondary battery electrode material which is a carbonaceous material having a multiphase structure obtained by the production method of the present invention, is preferably (002) ), The interplanar spacing d ₀₀₂ is 0.345 nm or less, the crystallite size Lc in the C-axis direction is 15 nm or more, and more preferably d ₀₀₂ is 0.340 n.
m or less, Lc is 50 nm or more, and more preferably Lc is 80 nm or more. Also, regarding the volume average particle size,
It is preferably 100 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less.

The carbonaceous material serving as the core is (1) an organic compound in an inert gas flow or in a vacuum at 300 to 3000 ° C., preferably 500 to 3000.
It decomposes by heating at a temperature of ℃, carbonization and graphitization. (2) Carbonaceous materials such as carbon black and coke are further heated to appropriately carbonize them. (3) Use artificial graphite, natural graphite, or vapor-grown graphite whiskers. And the like.

In the method (1), as the organic compound which can be used as a starting material, naphthalene, phenanthrene, anthracene, triphenylene, pyrene,
Fused polycyclic hydrocarbon compounds obtained by condensing two or more monocyclic hydrocarbon compounds having three or more membered rings, such as chrysene, naphthacene, picene, perylene, pentaphene, and pentacene; or carboxylic acids or carvone of the above compounds Derivatives such as acid anhydrides and carboxylic acid imides; various pitches containing a mixture of the above compounds as a main component can be mentioned.

The above pitch will be described in more detail below.
Ethylene heavy-end pitch generated during naphtha decomposition, crude oil pitch generated during crude oil decomposition, coal pitch generated during thermal decomposition of coal, asphalt decomposition pitch generated by asphalt decomposition, polyvinyl chloride, etc. Pitch etc. which are generated by thermal decomposition can be mentioned as an example. Further, these various pitches can be further heated under a flow of an inert gas or the like to form a mesophase pitch having a quinoline insoluble content of preferably 80% or more, more preferably 90% or more, still more preferably 95% or more. .

On the other hand, as the raw material for the carbonaceous material constituting the surface layer, there are 3 such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, picene, perylene, pentaphene and pentacene.
A condensed polycyclic hydrocarbon compound obtained by condensing two or more monocyclic hydrocarbon compounds each having at least one membered ring; or a derivative of the above compound such as a carboxylic acid, a carboxylic acid anhydride or a carboxylic acid imide; Various pitches containing a mixture as a main component can be mentioned.

The above pitch will be described in more detail below.
Ethylene heavy-end pitch produced during naphtha decomposition, crude oil pitch produced during crude oil decomposition, coal pitch produced during thermal decomposition of coal, asphalt decomposition pitch produced by asphalt decomposition, polyvinyl chloride, etc. Pitch etc. which are generated by thermal decomposition can be mentioned as an example.

It is preferable to stir these two types of carbonaceous materials in advance before firing to promote devolatilization and polycondensation of the surface layer material. In this case, the treatment temperature is preferably 100 to 600 ° C., and it is preferable to perform the treatment under reduced pressure in an inert atmosphere.

The raw material supplied to the firing furnace is preferably in powder form. The average particle size of the raw material is preferably 200μ
m or less, more preferably 100 μm or less, particularly preferably 50 μm or less.

The firing apparatus used in the present invention is preferably a tubular rotary furnace which rotates at an angle on a horizontal plane, a so-called rotary kiln. Further, it is preferable to apply only the rotational force by the wall surface of the furnace to the raw materials during firing, and it is preferable that the rotating furnace does not have a forced stirring means.

Firing in a firing furnace is carried out in an inert gas,
At the treatment temperature, carbonization of the carbonaceous material that constitutes the surface layer begins,
It is important that the temperature is higher than the temperature at which sintering does not occur even if heating is further performed. The processing temperature is preferably 700 ° C to 180 ° C.
The temperature is 0 ° C, more preferably 900 ° C to 1500 ° C, particularly preferably 900 ° C to 1300 ° C.

The number of rotations of the rotary tube is r
(M) and the number of revolutions is N (rpm), preferably 0.001 ≦ N / r ≦ 500, more preferably 0.0
1 ≦ N / r ≦ 100, particularly preferably 0.1 ≦ N / r ≦
50. The carbonaceous material after firing becomes powdery or granular. Even if it becomes granular, it is not hard and sintered,
It can be crushed easily.

In the case of crushing in the form of granules, it is desirable that the crushing energy is small and over-milling does not easily occur.
For example, a sieving machine equipped with a crushing mechanism such as rotary feathers and crushed balls can be used. In the case of this sieving machine with a crushing mechanism, the crushed powder is immediately sieved, so overcrushing does not easily occur.

The degree of coverage by the carbonized surface layer is
It can be known by spectroscopy. Carbonaceous matter is generally
Using an argon ion laser beam with a wavelength of 514.5 nm
Raman spectrum spectroscopy, 1580 cm^-1near
Peak and 1360 cm ^-1With a peak near 1
580 cm^-1Peak intensity I near₁₅₈₀Against 1360
cm^-1Peak intensity I near₁₃₆₀R value (I₁₃₆₀
/ I₁₅₈₀) Corresponds to the crystallinity, and the R value is the crystallinity.
It is known that the higher is the smaller. Also carbon
The Raman spectrum of the carbonaceous material is the surface or surface of the carbonaceous material.
The present invention is sensitive to structural changes in a portion very close to
For multi-phase carbonaceous materials such as
It serves as an indicator of the degree. In the present invention, the core is finally
The R value of the carbonaceous material having high crystallinity to be formed is 0.4 or less.
Of the desired and finally obtained multiphase carbon electrode material
R value must be greater than that of core carbonaceous material
Is preferable, and more preferably 0.5 or more.
Yes.

[0019]

[Example] 3 kg of artificial graphite powder (KS-44 manufactured by LONZA Co., Ltd.) was charged into a stainless steel tank having an internal volume of 20 liters, and further 7 kg of ethylene heavy end tar (Mitsubishi Chemical Co., Ltd.) obtained at the time of naphtha decomposition was added, and a hand mixer was used. The stainless steel container was bathed in hot water at 80 ° C. and stirred for 10 minutes in the same manner. The slurry mixture obtained here was manufactured by Kurimoto Iron Works using a measuring gear pump. 1kg / in one KRCS1 reactor
It was supplied by the hr and the coating material was subjected to a heat treatment pitching reaction. Keep the reactor temperature at 325 ° C and further reduce the pressure to 66
Degassing and devolatilization were performed at 0 mmHg to remove the light fraction of ethylene heavy end tar. The product, which is a semi-solid solution exhibiting high viscosity, was recovered in a strand form from the KRC reactor outlet at 0.5 kg / hr. Thus, a composite of carbonaceous material particles and heat-treated pitch was obtained. Further, pulverization was performed to obtain a powdery raw material for firing.

Next, an electrode material was obtained by firing at 1200 ° C. in a nitrogen stream using a rotary kiln (rotary tube furnace manufactured by Hirotsuki Co., Ltd.). The firing raw material was put into a rotary tube with a screw feeder. The rotary tube of the rotary kiln has an outer diameter of 100 mm and a length of 1500 mm.
It was operated at a tilt of 4 degrees and 5.1 rpm. The obtained carbonaceous material was hardly sintered, and even a lumpy or granular material could be easily crushed by hand.

X-ray diffraction and Raman spectroscopy were performed to examine the degree of baking and the surface structure. In X-ray diffraction, d ₀₀₂ calculated from the low-angle peak was 0.352 nm, Lc was 26 nm, and d ₀₀₂ calculated from the high-angle peak.
₀₀₂ was 0.336 nm, and Lc was 100 nm or more. The R value of Raman spectroscopy was 0.71. The R value of graphite KS-44 was 0.14, and it was determined that the surface was covered.

The electrode performance of this multi-phase carbonaceous material was evaluated by a charge / discharge test using lithium as a counter electrode. As a result, the capacity of the created 3 samples was 347.8 mAh / g, 34
5.2 mAh / g and 338.9 mAh / g, irreversible capacities 2.7 mAh / g, 2.1 mAh / g and 2.
It was 3 mAh / g.

[Comparative Example] An electrode material was prepared in the same manner as in the example, except that firing was carried out in a batch furnace and crushed by an impact crusher to obtain an electrode material. Firing in a batch furnace was performed at 1200 ° C. under a nitrogen stream. In X-ray diffraction,
D ₀₀₂ calculated from the low-angle peak is 0.350n
m and Lc were 49 nm, d ₀₀₂ calculated from the high-angle peak was 0.336 nm, and Lc was 100 nm or more. The R value of Raman spectroscopy was 0.44. The R value of the example is 0.71, and it is considered that the coating on the surface is destroyed by crushing.

The electrode performance was evaluated by a charge / discharge test using lithium as the counter electrode. As a result, the capacity of the three samples prepared was 317.3 mAh / g, 321.3 mAh / g and 3
19.2 mAh / g, irreversible capacity is 4.5 mAh / g,
It was 3.8 mAh / g and 4.3 mAh / g. Table 1 shows the physical property values and charge / discharge test results of Examples and Comparative Examples.
Shown in.

In the examples and comparative examples, various measurements were carried out as follows. (X-Ray Diffraction) If the carbonaceous material is powder, if it is in the form of small pieces, it is powdered in an agate mortar, and about 15 wt% of X-ray standard high-purity silicon powder is added to the sample and mixed, A wide-angle X-ray diffraction curve was measured by a reflection diffractometer method using CuKα rays that were packed in a sample cell and monochromated with a graphite monochromator as a radiation source. The obtained X-ray diffraction curve has a shape in which two peaks derived from different crystallinities are overlapped with each other. A relatively broad peak derived from the carbonaceous coating phase is present on the low angle side and a high angle side is exhibited on the high angle side. It has a relatively sharp peak derived from carbonaceous matter corresponding to the inner core. After separating the peaks from this diffraction curve, d ₀₀₂ and Lc were calculated for each peak.

(Raman spectroscopy) In Raman spectroscopy of a carbonaceous material using an argon ion laser beam having a wavelength of 514.5 nm, a peak near 1580 cm ^-1 and 1360 cm ^-1 were obtained.
^It has a peak near ^-1 . 1580 cm ^-1 peak intensity at around 1360 cm ^-1 to the peak intensity I ₁₅₈₀ near I
_The R value (I ₁₃₆₀ / I ₁₅₈₀ ) was determined by the ratio of ₁₃₆₀ .

(Charge / Discharge Test) A slurry was prepared by adding a thermoplastic elastomer to a carbonaceous material as a binder, and the slurry was applied onto a copper foil by a doctor blade method to prepare a sheet electrode. This electrode was punched into a disc shape, and a separator impregnated with an electrolytic solution was sandwiched between the electrodes to prepare a coin-shaped cell opposed to a lithium metal electrode, and a charge / discharge test was conducted. The electrolytic solution used was a solvent prepared by mixing ethylene carbonate and diethylene carbonate at a weight ratio of 1: 1 and dissolving lithium perchlorate at a ratio of 1.5 mol / liter.

In the charge / discharge test, charging was carried out until the potential difference between both electrode values became 0 V, and discharging was carried out to 1.5 V. As a result, the average discharge capacity of the initial 5 cycles and the irreversible capacity (difference between the charge capacity and the discharge capacity) were obtained up to the 5th cycle except the first 1 cycle.

[0029]

[Table 1]

[0030]

As is apparent from the above Examples and Comparative Examples, according to the method of the present invention, a carbonaceous material having a multiphase structure can be produced without exposing the nucleus by coating destruction, and excellent electrode performance is realized. it can.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiko Sugawara Keiko Sugawara 3-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Mitsubishi Chemical Corporation Tsukuba Research Institute (72) Takashi Kameda 8-chome, Ami-cho, Inashiki-gun, Ibaraki 3-1, Mitsubishi Chemical Co., Ltd. Tsukuba Research Laboratory (72) Inventor Shoichiro Mori 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Mitsubishi Chemical Co., Ltd. Tsukuba Research Laboratory (56) Reference JP 5-94838 ( (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/36-4/62 H01M 4/02-4/04 H01M 10/40

Claims (2)

(57) [Claims] 1. A carbonaceous material having a d ₀₀₂ of 345 nm or less,
After coating with an organic compound mainly composed of a condensed polycyclic compound 1
The carbon raw material obtained by heat treatment at 00 ° C to 600 ° C is placed under an inert gas atmosphere in a wall surface of a rotary tube of a rotary kiln.
The method for producing a multi-phase structure carbon electrode material, which comprises firing at 700 ° C. to 1800 ° C. while imparting rotational motion by 2. The inner diameter of the rotary tube of the rotary kiln is r
(M), when the number of rotations is N (times / minute), 0.001
The method for producing a multiphase structure carbon electrode material according to claim 1, wherein ≦ N / r ≦ 500.