JPH097598A - Carbon material for negative electrode of non-aqueous solvent secondary battery - Google Patents

Abstract

(57) [Summary] Carbon material for negative electrode of non-aqueous solvent secondary battery [Purpose] To provide a high-performance carbon material for negative electrode of non-aqueous solvent secondary battery with large capacity and little capacity loss. [Summary] After the lithium is occluded so that the atomic ratio of lithium to carbon (C / Li) is 4.5 or less, the shift values are 10 to 20 ppm and 110 in the NMR spectrum of lithium nuclei measured at -40 ° C. A carbon material for a negative electrode of a non-aqueous solvent secondary battery, wherein at least two kinds of peaks are observed at 140 ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon material for a negative electrode of a non-aqueous solvent secondary battery, which has a large capacity and is excellent in charge / discharge cycle characteristics.

[0002]

2. Description of the Related Art A non-aqueous solvent secondary battery using a carbon material as 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 and small size, and long-term storability. However, in order to support the reduction in size and weight of electronic equipment, improvements such as higher capacity are needed. Therefore, as described in JP-A No. 7-37590, a carbon material in which absorbed lithium exhibits a specific NMR peak has been studied. However, although these carbon materials have a large storage capacity, they also have a large capacity loss (difference between the storage capacity and the discharge capacity), and thus are not sufficient as a negative electrode for a non-aqueous solvent secondary battery.

[0003]

As described above, the conventional non-aqueous solvent secondary battery using the carbon material as the negative electrode material is not sufficient to realize the characteristic large capacity. The present invention solves the above problems of the prior art, can realize a large capacity, good charge and discharge cycle characteristics, stable, and excellent carbon material for non-aqueous solvent secondary battery negative electrode excellent in safety The purpose is to provide.

[0004]

Means and Action for Solving the Problems The present inventors have
In order to achieve the above object, as a result of examining various carbon materials described in conventional patents, etc., in the NMR spectrum of the occluded lithium nuclei, a carbon material having a specific shift value is a non-aqueous solvent. They have found that they have excellent properties as a negative electrode for secondary batteries, and have completed the present invention.

The carbon material for a non-aqueous solvent secondary battery negative electrode of the present invention is measured at −40 ° C. after occluding lithium so that the atomic ratio (C / Li) of carbon and lithium is 4.5 or less. The carbon material is characterized in that at least two kinds of peaks are observed at 10 to 20 ppm and 110 to 140 ppm in the NMR spectrum of the lithium nucleus, and the shift value is preferably 100 when measured at 27 ° C. It is a carbon material whose peak is observed at 120 ppm.

As a carbon material having the above characteristics,
A carbon material prepared by firing a raw material organic compound obtained by reacting at least one compound selected from condensed polycyclic compounds with a compound containing nitrogen, sulfur, oxygen and the like can be mentioned.

As the condensed polycyclic compound, naphthalene,
Anthracene, pyrene, condensed polycyclic hydrocarbon compounds such as coronene and derivatives thereof, benzofuran, quinoline, thianaphthalene, condensed heterocyclic hydrocarbon compounds such as silanaphthalene and derivatives thereof, compounds in which these compounds are mutually crosslinked, Further coal, which is a mixture of the above compounds,
Examples include coke, petroleum pitch, coal tar pitch, synthetic pitch, tar and similar heavy oils. In particular, pitch or tar having a softening point of 170 ° C. or lower is preferably used.

Examples of compounds containing nitrogen, sulfur, oxygen and the like include nitric acid, sulfuric acid, nitrating agents, nitro compounds, ammonium sulfate, ammonium persulfate, ammonium acid sulfate, nitrogen dioxide gas, ozone, air, oxygen and the like and mixtures thereof. Can be mentioned.

For the nitration reaction with a nitrating agent, a general method of nitrating an organic compound can be applied. For example, nitration can be performed using nitric acid and sulfuric acid or nitric acid and acetic anhydride. The nitration can also be performed by using oxygen or air containing nitrogen dioxide gas and ozone gas. The resulting nitrated product is washed with water to remove the acid,
dry.

The nitro compound is preferably an aromatic nitro compound, and particularly preferably dinitronaphthalene. The optimum weight ratio of the nitro compound to the fused polycyclic compound is appropriately selected, but for example, in the case of dinitronaphthalene and pitch, it is preferably about 0.1 to 3. Regarding the reaction temperature, an optimum value is appropriately selected, but usually 200
６００600 ° C.

Also when ammonium sulfate is used, the optimum weight ratio is appropriately selected, but in the case of pitch, it is 0.1.
About 3 is preferable. Regarding the reaction temperature, an optimum value is appropriately selected, but it is usually 200 to 600 ° C.

Oxidation may be performed using air, oxygen or the like.

The carbon material of the present invention can be obtained by firing the raw material organic compound thus obtained under a non-oxidizing gas or vacuum. Firing temperature is 800 ~ 1800
℃, preferably 1000 ℃ ~ 1300 ℃, firing time is 1
Optimum conditions are appropriately selected depending on the composition of the raw material organic compound in 50 hours. Further, pre-baking may be performed at 800 ° C. or lower, and it is particularly preferable to perform pre-baking twice at 600 ° C. or lower and 800 ° C. Nitrogen and argon are preferable as the non-oxidizing gas. A method in which a non-oxidizing gas is continuously supplied as an air flow and a gas generated by firing of the raw material organic compound is discharged together, or a method in which the generated gas is forcibly discharged out of the system by evacuation can be appropriately applied. Most preferably, firing is performed while maintaining the vapor partial pressure of the generated gas at 30 mmHg or less.

The carbonaceous material for a negative electrode of a non-aqueous solvent secondary battery of the present invention has various excellent characteristics. In particular, it is 450 (mAh / g) between 0 and 1.5 (V) with respect to the Li potential. ) The discharge capacity above is possible and the capacity loss is 200 (mA
h / g) or less.

Hereinafter, the effects of the present invention will be described specifically and in detail by showing Examples and Comparative Examples.
The following examples are for illustrative purposes only and are not intended to limit the embodiments or the scope of the invention. Further, various analysis methods and analysis conditions of the negative electrode material in this example are described below.

[Nuclear Magnetic Resonance (NMR) Spectrum Measurement]
Measurement frequency of 15 using JMN-400 manufactured by JEOL Ltd.
5.25MHz, MASGNN mode, rotation speed about 5k
It was measured at Hz and 64 times of integration. Using LiCl powder as an external standard sample, the observed Li ⁺ peak was-
It was 1.19 ppm. In addition, −1.19 ppm is a shift value of LiCl powder when LiCl is dissolved in heavy water to a concentration of 1 (mol / l) as a standard. For the sample preparation, a carbon material was used, and the counter electrode was metallic lithium,
Electrolysis was performed by electrochemically absorbing lithium using an electrolyte obtained by dissolving LiPF _{6 in an} equimolar mixed solvent of ethylene carbonate and dimethyl carbonate. The sample was washed with a solvent, dried in vacuum, sealed in a sample tube for measuring solid, and then measured.

[Measurement of Particle Size Distribution] SYMPATEC HE
It was measured by a dry laser diffraction method using LOS.
The 50% cumulative diameter was defined as the average particle diameter.

[Carbon content] A 2400 CHN type elemental analyzer manufactured by Perkin Elmer was used as an analyzer.
The measurement is performed by placing the negative electrode material of the sample in a tin container at 1.5 ± 0.2.
mg was precisely weighed, set in the apparatus, burned at a temperature of 975 ° C. for 5 minutes, and detected and measured by TCD with a He gas carrier. In addition, in the measurement of the sample, it was corrected in advance with acetanilide (2.0 ± 0.1 mg) as a standard substance.

[0019]

【Example】

Example 1 A naphthalene 1 was added to an acid-resistant autoclave having an internal volume of 500 ml.
Mole, hydrogen fluoride (HF) 0.5 mole boron trifluoride (BF)
₃ ) Charge 0.5 mol and pressurize to 200 kg under a pressure of 25 kg / cm ^2.
After the temperature was raised to 0 ° C., the temperature was kept at 200 ° C. for another 2 hours for reaction. Then, according to a conventional method, nitrogen was blown into the autoclave to recover HF and BF ₃ , and low boiling point components were subsequently removed to obtain a pitch having a softening point of 115 ° C. Subsequently, 100 parts by weight of the obtained pitch was mixed with 100 parts by weight of dinitronaphthalene while heating at 180 ° C., and the temperature was further raised to 400 ° C. After cooling to room temperature, it was ground to an average particle size of 15 μm. Then, it was fired in a nitrogen gas stream at 1200 ° C. for 2 hours to obtain a powdery carbon material. The carbon content was 95.7 wt%.

[Evaluation as Negative Electrode Material] 100 parts by weight of the obtained carbon material was mixed and mixed with 5 parts by weight of polyfluoroethylene powder [binder] and compression molded into a disc shape to prepare a flexible molded body. A test piece for evaluation was used. Then,
A solution of LiPF ₆ dissolved in an equal volume mixture of ethylene carbonate and dimethyl carbonate [concentration 1.0 mol / l
] Was used as an electrolytic solution, and a half cell was prepared using a polypropylene microporous film having a thickness of 50 μm as a separator. In addition,
A 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 the reference electrode as in the case of the counter electrode.

At a current density of 2.0 mA / cm ² , constant current charging was performed until the electrode potential of the evaluation test piece for the reference electrode was 1 mV, and further constant voltage charging was performed at an electrode potential of 1 mV for 20 hours.
As a result, a storage capacity of 630 mAh / g (per 1 g of carbon material) was confirmed. Next, current density 1.0mA
/ Cm at which the electrode potential of the test pieces for evaluation with respect to ² by the reference electrode was subjected to constant current discharge to 1.5V discharge capacity: 5
10 mAh / g was confirmed. That is, the capacity loss is 1
It was 20 mAh / g.

Using a test piece (C / Li = 3.4) occluding lithium up to 630 mAh / g, the NMR spectrum of lithium nuclei was measured at -40 ° C., and the shift values were at least 15.8 ppm and 126.0 ppm. Two
Different types of peaks were observed. Further, when measured at 27 ° C., a peak was observed at a shift value of 112.5 ppm.

Example 2 100 parts by weight of coal tar pitch having a softening point of 110 ° C. and 35 parts by weight of ammonium sulfate were heated to 130 ° C., mixed with an extruder, and further heated to 450 ° C. in a reactor. After cooling to room temperature, it was ground to an average particle size of 15 μm. Then, it was fired in a nitrogen gas stream at 1050 ° C. for 2 hours to obtain a powdery carbon material. Carbon content is 94.7wt
%Met. When evaluated as a negative electrode material in the same manner as in Example 1, the storage capacity: 670 (mAh /
g), the discharge capacity was 530 (mAh / g), and the capacity loss was 140 mAh / g. Furthermore, 670 mAh
/ G of lithium occluded lithium (C / Li = 3.
When the NMR spectrum of lithium nuclei was measured using 2) at -40 ° C, the shift value was 15.6 ppm and 1
At least two peaks were observed at 25.8 ppm. Further, when measured at 27 ° C., the shift value was 111.
A peak was observed at 8 ppm.

Comparative Example 1 Cupric chloride, aluminum chloride and benzene were mixed in a molar ratio of 1: 1: 4 and stirred in a nitrogen atmosphere. The obtained powder was washed, vacuum dried, and then fired at 700 ° C. in a hydrogen stream. The carbon content was 91.8 wt%. When evaluated as a negative electrode material in the same manner as in Example 1, the storage capacity was 950 (mAh / g) and the discharge capacity was 420 (mAh / g), and the capacity loss was 530 m.
Ah / g was reached. Furthermore, the NMR spectrum of lithium nuclei was measured using a test piece (C / Li = 2.2) which occluded lithium up to 950 mAh / g, and the shift value was 9.5 ppm at -40 ° C and 9.50 at 27 ° C. 8
A broad peak was observed at ppm.

[0025]

According to the present invention, a high-performance carbon material for a negative electrode of a non-aqueous solvent secondary battery having a large capacity and a small capacity loss can be obtained.

Claims (2)

[Claims] 1. After occluding lithium so that the atomic ratio (C / Li) of carbon and lithium is 4.5 or less, -40
Shift values of 10 to 20 ppm and 110 to 140 pp in the NMR spectrum of lithium nuclei measured at
A carbon material for a negative electrode of a non-aqueous solvent secondary battery, wherein at least two types of peaks are observed in m. 2. After occluding lithium so that the atomic ratio (C / Li) of carbon to lithium is 4.5 or less, 27 ° C.
The carbonaceous material for a non-aqueous solvent secondary battery negative electrode according to claim 1, wherein a peak is observed at a shift value of 100 to 120 ppm in the NMR spectrum of the lithium nucleus measured in 1.