JPH10308220A - Manufacture of carbon material for negative electrode of non-aqueous solvent secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon material for negative electrode, which has a high capacity and which can lower the irreversible capacity in a first cycle, by reforming precursor pitch or tar, which is obtained by polymerizing condensation polycyclic compound in the existence of hydrogen fluoride and boron trifluoride, so as to prepare the isotropic reformed pitch or tar, and performing the infusible processing with the oxidant gas, and thereafter, burning it. SOLUTION: As a precursor pitch or tar, a pitch and a tar, which has a softening point at 0-200 deg.C, atomic ratio of hydrogen to carbon at 0.60-1.10, pyridine insoluble matter at 1.0% or less and ratio of aliphatic hydrogen in the whole of hydrogen included in the pitch or tar at 20-80%, is desirable. Reform of the pitch or the tar is easily and effectively performed by flowing air in the pitch and the tar. At the time of infusible processing, stay of the impure material after burning is reduced by using the oxidant gas, and especially, air is easily and desirably used, and processing is performed at 100-400 deg.C of temperature range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a carbon material for a negative electrode of a non-aqueous solvent secondary battery having a large capacity and a small irreversible capacity.

[0002]

2. Description of the Related Art A non-aqueous solvent secondary battery using a carbon material for a negative electrode has already been put into practical use as a lithium ion secondary battery because of its advantages such as high energy density, light weight, small size and long-term storage. However, it is necessary to increase the capacity of the carbon material for the negative electrode in order to cope with the reduction in size and weight of electronic devices. Therefore, for example, as described in JP-A-6-187988, by reacting pitch or tar with a nitro compound, a high-capacity carbon material having a discharge capacity per weight exceeding 500 mAh / g has been found. Issued and considered. However, there is a great demand for the development of a lithium ion secondary battery that can be operated for a longer time, and conventional materials have been insufficient to meet the demand for capacity. So far, it has been found that coke fired at a low temperature or polyacene fired with phenolic resin has a high capacity. The difference between the charge capacity and the discharge capacity at
It was not enough to meet the demand. Furthermore, at the time of discharge,
Since the potential of the negative electrode material with respect to lithium metal is high, a major drawback is that the average voltage when a secondary battery is designed in combination with the positive electrode material is low.

[0003]

As described above, the conventional non-aqueous solvent-based lithium secondary battery using a carbon material as a negative electrode material is not sufficient for realizing a large capacity which is a characteristic of the non-aqueous solvent-based lithium secondary battery. Was. SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned conventional problems and provides a high-capacity, high-performance non-aqueous solvent secondary battery with good charge / discharge cycle characteristics and excellent stability and safety. ) Having a high capacity of 500 mAh / g or more per weight, 2) reducing the irreversible capacity of the carbon material for the negative electrode in the first cycle, and 3) reducing the potential of the negative electrode material to lithium metal at the time of discharge to 0.2 V or less. An object is to provide a carbon material for a negative electrode having a large capacity in a certain region.

[0004]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies on a high-capacity carbon material for a negative electrode using pitch or tar as a raw material. A carbon material obtained by modifying a specific precursor pitch or tar obtained by synthesis from a substance containing, and further processing by a specific infusibilization method, and then firing is excellent as a negative electrode of a non-aqueous solvent secondary battery. It has been found that the present invention has such properties, and the present invention has been completed.

The method for producing a carbon material for a negative electrode of a non-aqueous solvent secondary battery according to the present invention is obtained by polymerizing a condensed polycyclic compound or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride. A non-aqueous solvent secondary battery characterized by preparing an isotropic modified pitch or tar by modifying a specific precursor pitch or tar, infusibilizing it with an oxidizing gas, and then firing. This is a method for producing a carbon material for a negative electrode.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As condensed polycyclic compounds, condensed polycyclic hydrocarbons such as naphthalene, anthracene, pyrene, coronene and derivatives thereof, and condensed heterocyclic compounds such as benzofuran, quinoline, thianaphthalene, silanaphthalene, etc. And derivatives thereof, compounds in which these compounds are cross-linked to each other, and various petroleum fractions which are mixtures thereof,
Examples include the residual oil of the petroleum processing step and the coal tar fraction.

The method of synthesizing the precursor pitch or tar from the condensed polycyclic compound in the presence of a hydrogen fluoride / boron trifluoride catalyst is not particularly limited. 0.1 to 10 mol of hydrogen fluoride, 0.01 to 1.0 mol of boron trifluoride, and the reaction temperature is in the range of 0 to 300 ° C, preferably 40 to 100 mol per mol of the cyclic compound.
The reaction is performed at 200 ° C, more preferably at 60 to 170 ° C.

As a property of the precursor pitch or tar obtained from the condensed polycyclic compound, the softening point is 0 to 20.
0 ° C. is preferable, and the atomic ratio of hydrogen to carbon is 0.6 to
1.10, pyridine-insoluble matter is preferably 1.0% or less, and the proportion of aliphatic hydrogen in all hydrogen contained in pitch or tar is preferably 20 to 80%. After polishing the precursor pitch or tar by a conventional method, the optical structure when observed under a polarizing microscope is 100% isotropic.

Next, the precursor pitch or tar is processed into a modified pitch or tar having a softening point of 150 ° C. or higher while maintaining optical isotropy. The reforming can be performed by a known method such as distillation, air blowing, addition of nitric acid, and addition of sulfur. Among them, a method in which an oxidizing gas, generally air is passed through pitch or tar in a fluidized state under heating is simple, inexpensive and effective. Although the temperature at this time cannot be specified unconditionally by the softening point of the precursor pitch or tar, it is carried out at 200 ° C. or more, preferably 300 to 350 ° C. If the treatment temperature is too low, the reactivity is low, and the reforming with air is not performed sufficiently. On the other hand, if the temperature is too high, thermal polymerization of the pitch itself occurs, and reforming with air is not effectively performed. The air flow varies depending on the device shape, etc.
It is about 0.5 to 50 ml / g with respect to pitch or tar. At this time, use of a mesh or a filter or stirring may be applied to increase the contact efficiency between the pitch or tar and the air. Since the end point of the reforming by air involves an increase in the softening point, it can be determined by measuring the softening point. Although the softening point at the end point of the reforming cannot be specified by the starting material or the like, it is 150 to 350 ° C., preferably 2 to
00-300 ° C.

[0010] The infusibilizing treatment includes nitrogen dioxide gas, ozone,
Use of an oxidizing gas such as air, oxygen, or a mixture thereof is preferable for the performance of the obtained carbon material with less impurities remaining after firing. In particular, it is more preferable to use air gas because it is simple and inexpensive. The method of infusibilizing with an oxidizing gas is not particularly limited, but after processing the modified pitch into a powder, fibrous, or thin film ground to a certain particle size or less, a temperature range of 100 to 400 ° C., preferably 150 to 400 ° C. This is performed by flowing an oxidizing gas in a temperature range of 350 ° C.

The raw material organic compound thus obtained is calcined under a non-oxidizing gas or under vacuum to obtain the carbon material of the present invention. Firing temperature is 800 ~ 1800
° C, preferably 1000-1300 ° C, firing time is 1 ~
In 50 hours, optimal conditions are appropriately selected according to the starting organic compound. Further, preliminary firing may be performed at 800 ° C. or lower. Nitrogen and argon are preferable as the non-oxidizing gas. A method in which a non-oxidizing gas is continuously supplied as an air stream and a gas generated by baking the raw material organic compound is discharged together with the gas, or a method in which the generated gas is forcibly discharged to the outside by evacuation can be appropriately applied. .

The carbon material for a negative electrode of a non-aqueous solvent-based secondary battery of the present invention has various excellent characteristics. In particular, a carbon material having a discharge potential of 500 mAh / g or more between 0 and 1.5 V with respect to lithium metal potential. While the capacity is possible, the capacity between 0 and 0.2 V with respect to the lithium metal potential is 350 mAh / g or more, and the irreversible capacity in the first cycle is 100 mAh.
/ G or less is the most significant feature.

Hereinafter, the effects of the present invention will be described specifically and in detail with reference to examples.
It is for the purpose of specific description and is not intended to limit the embodiments or the scope of the invention. The method and conditions for analyzing pitch or tar in this example are described below. (Elemental analysis) For simultaneous analysis of carbon, nitrogen, and hydrogen, use a PerkinElmer 2400 analyzer.
A CHN-type elemental analyzer was used. In the measurement, 1.5 ± 0.2 mg of the pitch or tar of the sample was weighed in a tin container, set in the apparatus, burned at a temperature of 975 ° C. for 5 minutes, and detected and measured by TCD using a He gas carrier. Before measuring the sample, the standard substance acetanilide (2.
0 ± 0.1 mg).

[0014] To determine the percentage of aliphatic hydrogen in the total hydrogen contained in (NMR analysis) pitch or tar, ¹
The H-NMR method was used. Since almost all the pitch or tar is soluble in chloroform, a 1% deuterated chloroform solution was put into an NMR sample tube, and the measurement was performed using JNM-EX270 manufactured by JEOL Ltd. In addition, TMS (tetramethylsilane) is used as a reference substance,
This was set to 0 ppm.

Example 1 In a 3 L acid-resistant autoclave, 7 mol of naphthalene, 2.45 mol of hydrogen fluoride (HF), and boron trifluoride (BF) were added.
₃ ) After charging 0.77 mol, the temperature was raised to 100 ° C. under autogenous pressure, and the mixture was further reacted at 100 ° C. for 4 hours. Next, HF and BF ₃ were recovered by blowing nitrogen into the autoclave according to a conventional method, followed by removing low boiling components to obtain a precursor pitch having a softening point of 82 ° C. The ratio (H / C) of hydrogen atoms to carbon atoms contained in the precursor pitch is 0.76, the pyridine-insoluble content is 0.0%, and the proportion of aliphatic hydrogen in the total hydrogen contained in the pitch is 35%.
Met. The obtained precursor pitch was charged into another autoclave, and air was blown at 2 L / min at 340 ° C. per 100 g and reacted for 4 hours.
% Modified pitch with optical isotropy was obtained. The modified pitch is pulverized into powder having a size of 200 μm or less, and 10 g is placed in a porcelain dish.
After the temperature was raised from 320 ° C. to 320 ° C. at a rate of 1 ° C./min, it was taken out for 30 minutes. The obtained treated material was adjusted to an average particle size of 15 μm, and then 10 To
The powder was calcined at 1200 ° C. for 2 hours under a reduced pressure of rr to obtain a powdery carbon material.

(Evaluation as Negative Electrode Material) To 90 parts by weight of the obtained carbon material, 10 parts by weight of polyvinylidene fluoride powder (binder) were added, mixed and mixed with dimethylformamide as a solvent, and then coated on a copper foil. 1cm after drying
It was cut into a corner to obtain a test piece for evaluation. Then, LiC
The mixing ratio of 10 ₄ with ethylene carbonate / dimethyl carbonate / diethyl carbonate is 1 / 0.5 / 0.
5 dissolved in three kinds of mixture (concentration 1.0 mol / l
) Was used as an electrolyte to prepare a half cell using a 50 μm-thick polypropylene microporous membrane as a separator. Note that lithium metal having a diameter of 16 mm and a thickness of 0.5 mm was used as a counter electrode. A small piece of lithium metal was used as a reference electrode in the same manner as the counter electrode.

At a current density of ² mA / cm ² , the test piece for evaluation with respect to the reference electrode was charged at a constant current up to an electrode potential of 1 mV, and further charged at a constant potential of 1 mV for 40 hours. The occlusion capacity: 595 mAh / g Was confirmed.
Next, a constant current discharge was performed at a current density of 1 mAh / cm ³ until the electrode potential of the test piece for evaluation with respect to the reference electrode was 1.5 V. As a result, a discharge capacity of 531 mAh / g was confirmed.
The capacity loss was 64 mAh / g, and the release capacity between 0 and 0.2 V relative to lithium metal potential was 369 mAh / g.

Example 2 1 mol of anthracene, 2.50 mol of hydrogen fluoride (HF) and 0.20 mol of boron trifluoride (BF ₃ ) were charged into an acid-resistant autoclave having a content volume of 500 mL, and the mixture was heated to 80 ° C. under autogenous pressure. After the temperature was raised, the reaction was maintained at 80 ° C. for further 4 hours. Next, HF and BF ₃ were recovered by blowing nitrogen into the autoclave according to a conventional method, and subsequently, low boiling components were removed to obtain a precursor pitch having a softening point of 193 ° C. The ratio (H / C) of hydrogen atoms to carbon atoms contained in the precursor pitch is 0.63, the pyridine-insoluble content is 0.0%,
The proportion of aliphatic hydrogen in the total hydrogen contained in the pitch is 45
%Met. The obtained precursor pitch was charged into another autoclave, and air was blown at 2 L / min at 340 ° C. per 100 g and reacted for 1 hour.
A 0% optically isotropic modified pitch was obtained. This modified pitch is pulverized into powder having a size of 200 μm or less, and 10 g is placed in a porcelain dish.
After the temperature was raised from 0 ° C. to 320 ° C. at 1 ° C./min, it was taken out for 10 minutes. The obtained processed product was treated with an average particle size of 15 μm.
And 10T while passing a small amount of nitrogen through.
The powder was calcined at 1200 ° C. for 2 hours under a reduced pressure of orr to obtain a powdery carbon material. When the same negative electrode material was evaluated as in Example 1, an occlusion capacity of 626 mAh / g and an emission capacity of 543 mAh / g were confirmed. The capacity loss is 83 mAh / g, and 0 to
The emission capacity during 0.2 V was 380 mAh / g.

Comparative Example 1 100 parts by weight of the modified pitch obtained in Example 1 and 35 parts of ammonium sulfate were mixed in a powder state, heated to 450 ° C., kept for 1 hour, and then cooled to room temperature. The obtained processed product was pulverized to an average particle size of 15 μm. Then, under a reduced pressure of 10 Torr, 120
The powder was fired at 0 ° C. for 2 hours to obtain a powdery carbon material. When an evaluation as a negative electrode material was performed in the same manner as in Example 1, an occlusion capacity: 570 mAh / g and an emission capacity: 485 mA
h / g was confirmed. Although the capacity loss was as small as 85 mAh / g, the emission capacity was 500 mAh / g or less, and the emission capacity between 0 and 0.2 V with respect to lithium metal potential was 29 mAh / g.
It was as small as 0 mAh / g.

Comparative Example 2 The ratio of hydrogen atoms contained to carbon atoms (H /
C) 0.95, a pyridine-insoluble content of 0.0%, and a ratio of aliphatic hydrogen in the total hydrogen contained in the pitch of 57% to ethylene bottom oil, and the presence of hydrogen fluoride and boron trifluoride Without performing the reaction below, the mixture was charged into an autoclave as it was, and air was blown at a rate of 2 L / min at 340 ° C. per 100 g and reacted for 2 hours, and a 100% optically isotropic pitch having a softening point of 260 ° C. I got This modified pitch is 20
Pulverize to a powder of 0 μm or less, put 10 g in a porcelain dish,
The temperature was raised from 150 ° C. to 300 ° C. at a rate of 3 ° C./min while flowing 1 L of air per minute in a muffle furnace, followed by holding for 10 minutes and taking out. The obtained treated product was adjusted to an average particle size of 15 μm, and then 10 Torr while flowing a small amount of nitrogen.
The powder was calcined at 1200 ° C. for 2 hours under reduced pressure to obtain a powdery carbon material. When the same negative electrode material was evaluated as in Example 1, an occlusion capacity of 625 mAh / g and an emission capacity of 459 mAh / g were confirmed. That is, the capacity loss was as large as 166 mAh / g, and the charge / discharge capacity was also reduced. The discharge capacity between 0 and 0.2 V with respect to the lithium metal potential was as small as 280 mAh / g.

Comparative Example 3 In an acid-resistant autoclave having a volume of 3 L, 7 mol of naphthalene, 2.45 mol of hydrogen fluoride (HF) and boron trifluoride (BF) were added.
₃ ) After charging 0.77 mol, the temperature was raised to 230 ° C. under the autogenous pressure, and the reaction was further maintained at 230 ° C. for 4 hours. Subsequently, nitrogen was blown into the autoclave to recover HF and BF ₃ according to a conventional method, and subsequently low boiling components were removed to obtain a precursor pitch having a softening point of 210 ° C. The ratio (H / C) of hydrogen atoms to carbon atoms contained in the pitch was 0.68, and the pyridine-insoluble content was 18.0%. In addition, the ratio of the aliphatic hydrogen in the total hydrogen contained in the pitch could not be measured because the entire pitch was not dissolved in the solvent. The obtained precursor pitch was charged into another autoclave, and 2 L of air was blown per minute at 340 ° C. per 100 g and reacted for 2 hours to obtain a pitch having a softening point of 240 ° C. After polishing the pitch by a conventional method, when observed under a polarizing microscope, about 50% of the optical structure showed anisotropy. This modified pitch is pulverized into powder of 200 μm or less,
Put 10 g in a porcelain dish and air in a muffle furnace at 1 minute per minute.
While flowing L, the temperature was raised from 150 ° C. to 320 ° C. at 1 ° C./min, and then held for 10 minutes and taken out. The obtained treated material was adjusted to an average particle size of 15 μm, and then passed at 1200 ° C. under a reduced pressure of 10 Torr while flowing a small amount of nitrogen.
After firing for a time, a powdery carbon material was obtained. When an evaluation as a negative electrode material was performed in the same manner as in Example 1, the occlusion capacity:
520 mAh / g and a release capacity of 384 mAh / g were confirmed. That is, the capacity loss was as large as 136 mAh / g, and the charge / discharge capacity was also reduced. The discharge capacity between 0 and 0.2 V with respect to the lithium metal potential was as small as 230 mAh / g.

[0022]

As compared with the conventional lithium secondary battery, the discharge capacity of the carbon material for the negative electrode is large and the irreversible capacity in the first cycle can be reduced, so that a large capacity of the secondary battery can be realized.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Joh Takahashi 22nd Wadai, Tsukuba, Ibaraki Prefecture Mitsubishi Gas Chemical Co., Ltd. Within the Research Institute (72) Inventor Norio Oishi 22nd Wadai, Tsukuba, Ibaraki Prefecture Mitsubishi Gas Chemical Co., Ltd. (72) Inventor Takaaki Higashiizumi 22nd Wadai, Tsukuba, Ibaraki Prefecture (72) Inventor Kyoko Shibahara 22nd Wadai, Tsukuba City, Ibaraki Prefecture Mitsubishi Gas Chemical Company, Ltd.

Claims (3)

[Claims] 1. A precursor prepared by polymerizing a condensed polycyclic compound or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride to modify a precursor pitch or tar.
A method for producing a carbon material for a negative electrode of a non-aqueous solvent secondary battery, comprising subjecting a 00% optically isotropic modified pitch or tar to an infusibilization treatment in the presence of an oxidizing gas, followed by firing. 2. The softening point of the precursor pitch or tar is 0.
~ 200 ° C, the atomic ratio of hydrogen to carbon is 0.60
The non-aqueous solvent secondary battery negative electrode according to claim 1, wherein 1.10, a pyridine-insoluble content is 1.0% or less, and a ratio of aliphatic hydrogen to total hydrogen contained in pitch or tar is 20 to 80%. Manufacturing method of carbon material. 3. The method for producing a carbon material for a negative electrode of a non-aqueous solvent secondary battery according to claim 1, wherein the infusibilization treatment is performed at a temperature of 100 ° C. or more and 400 ° C. or less.