JP3496901B2 - Carbonaceous materials for secondary battery electrodes - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbonaceous material for a secondary battery electrode, and more specifically to a high energy density non-aqueous solvent secondary battery electrode material having a large doping capacity of a battery active material. And a method for producing the same.

[0002]

2. Description of the Related Art As a high energy density secondary battery, a non-aqueous solvent type lithium secondary battery using a carbonaceous material as a negative electrode has been proposed (for example, JP-A-57-20807).
No. 9, JP-A-62-90863, JP-A-62.
-122066, Japanese Patent Laid-Open No. 2-66856). This utilizes the fact that a carbon intercalation compound of lithium can be easily formed electrochemically, and when this battery is charged, lithium in a positive electrode made of a chalcogen compound such as LiCoO ₂ is electrochemically converted into a negative electrode carbon. Is doped between the layers. Then, the carbon doped with lithium acts as a lithium electrode, and lithium is dedoped from the carbon layer and returns into the positive electrode with discharge.

A carbonaceous material as such a negative electrode material,
Alternatively, even in a carbonaceous material as a positive electrode material that is doped with a lithium source, the amount of electricity that can be used per unit weight is determined by the lithium dedoping amount. It is desirable to increase the amount.

It is known that a carbonaceous material obtained by firing a phenol resin or a furan resin has a large lithium doping amount and is preferable in this respect. However, when a negative electrode is formed by using a carbonaceous material obtained by firing a phenol resin or a furan resin, the lithium doped in the negative electrode carbon is not completely dedoped, and a large amount of lithium remains in the negative electrode carbon. However, there is a problem that the active material, lithium, is wasted.

When the electrode is made of graphite or a carbonaceous material having a developed graphite structure, when the carbonaceous material is doped with lithium, a graphite intercalation compound is formed and the graphite layer spacing is widened. By dedoping the lithium doped between the layers, the graphite layer spacing is restored. Therefore, in a carbonaceous material with a developed graphite structure, lithium doping-
Repeated dedoping easily causes breakage of graphite crystals.
Therefore, it is said that the secondary battery formed by using graphite or a carbonaceous material having a developed graphite structure is inferior in repeated charge / discharge performance. Further, it has been pointed out that in a battery using such a carbonaceous material having a developed graphite structure, the electrolytic solution is likely to decompose during operation of the battery.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and has a large charge / discharge capacity, and is an irreversible active material which is required as the difference between the doping capacity and the dedoping capacity. An object of the present invention is to provide a carbonaceous material for a secondary battery electrode that enables a non-aqueous solvent-based secondary battery that has a small capacity and effectively uses an active material, and a method for producing the same.

[0007]

The present inventors have a large charge / discharge capacity, excellent charge / discharge cycle characteristics, and irreversible capacity by appropriately controlling the crystal structure and fine structure of the carbonaceous material. It has been found that a carbonaceous material that enables a non-aqueous solvent-based secondary battery with a small (high utilization rate of active material) is obtained.

That is, the carbonaceous material for a non-aqueous solvent-based secondary battery electrode of the present invention was obtained by an X-ray diffraction method (00
2) Helium with respect to the average layer surface spacing (hereinafter sometimes abbreviated as “d002”) of 0.365 nm or more and the density (hereinafter sometimes abbreviated as “ρ _B ”) measured using butanol as a replacement medium. The ratio (hereinafter sometimes abbreviated as "ρ _H / ρ _B ") of the density (hereinafter sometimes abbreviated as "ρ _H ") measured using gas as a displacement medium is 1.
It is characterized by being 25 or more .

The carbonaceous material having such characteristics has a boiling point of 20 as an additive to petroleum-based or coal-based pitch.
One or two or more aromatic compounds having 2 to 3 rings having a temperature of 0 ° C. or higher are added, heated, melt-mixed, and then molded to obtain a pitch molded product, which has a low solubility in pitch and is added. The additive is extracted and removed from the pitch molded product with a solvent having a high solubility for the agent, and the obtained porous pitch is oxidized, and then 900 ° C under a reduced pressure of 10 kPa (0.1 atm) or less.
It can be manufactured by firing at a temperature of ˜1500 ° C. It can also be produced by firing palm shell char at a temperature of 900 ° C to 1500 ° C under a reduced pressure of 10 kPa or less.

According to the method of the present invention, an additive such as naphthalene is added to the pitch, the mixture is heated and melted and mixed, and then the additive is extracted and removed from the pitch molded body obtained by cooling to obtain fine particles in the pitch. Pores can be formed. The porous pitch thus obtained can be converted into a carbonaceous material while maintaining the fine pores formed in the pitch by oxidizing the porous pitch to make it infusible to heat and then firing it. . Further, by performing the firing under reduced pressure, it is possible to easily dissipate the decomposition gas and the tar component produced during firing and to promote the production of fine pores. The carbonaceous material produced in this manner has a large proportion of open pores (pores into which helium can enter), a large ρ _H , and a large ρ _H / ρ _B. The carbonaceous material of the present invention has a lithium doping capacity much higher than the value calculated from the lithium graphite intercalation compound LiC ₆ . Therefore, in the carbonaceous material of the present invention, it is considered that lithium doped in carbon is present in the carbonaceous material even in a state other than the graphite intercalation compound. It is presumed that open pores of a size that allows helium to enter but not butanol to contribute to the doping and dedoping of lithium in a state other than the graphite intercalation compound.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The first characteristic to be satisfied by the carbonaceous material of the present invention is that the average layer spacing d _{002 of} (002) planes obtained by X-ray diffraction is 0.365 nm or more. When a non-aqueous solvent-based secondary battery is constructed using a carbonaceous material having a d ₀₀₂ of less than 0.365 as a negative electrode, the dope capacity of the battery active material becomes small, and the carbonaceous material is likely to collapse due to repeated charging / discharging. Absent. Also, d ₀₀₂
A carbonaceous material having a value of more than 0.400 nm is not preferable because the irreversible capacity of the active material, which is required as the difference between the doping capacity and the dedoping capacity, becomes large. d ₀₀₂ is preferably 0.370 nm or more and 0.395 nm or less, more preferably 0.375 nm or more and 0.390 nm or less.

The second characteristic that the carbonaceous material of the present invention should have is a density ρ _B measured using butanol as a displacement medium.
Density ρ measured with helium gas as replacement medium for
The ratio of _H , ρ _H / ρ _B, is 1.25 or more .

The value of ρ _H / ρ _B is one index of the pore structure of the carbonaceous material, and a large value means that butanol cannot enter but helium can enter many pores. Means That is, a large ρ _H / ρ _B means that many fine pores exist. Further, if there are many closed pores (closed pores) such that helium cannot enter, ρ _H / ρ _B becomes small.

[0014] ratio [rho _{H /} [rho carbonaceous material such as _B is less than 1.25, undesirable since the doping amount and dedoping amount of battery active material is reduced.

In addition to the above essential requirements, the carbonaceous material of the present invention preferably further has the following characteristics.

One is that the atomic ratio H / C of hydrogen / carbon (hereinafter sometimes abbreviated as "H / C") by the elemental analysis of the carbonaceous material is 0.1 or less. The carbonaceous material generally decreases in H / C as the final heat treatment temperature rises during its production. A carbonaceous material having an H / C exceeding 0.1 is not preferable because the irreversible capacity of the active material, which is required as the difference between the doping capacity and the dedoping capacity of the active material, becomes large. H / C is more preferably 0.08 or less,
More preferably, it is 0.06 or less.

Further, in the carbonaceous material of the present invention, the crystallite size in the c-axis direction (hereinafter referred to as “Lc
₍₀₀₂₎ ”may be abbreviated. ) Is preferably 15 nm or less. Carbonaceous materials can be roughly classified into two types: graphitizable carbonaceous materials and nongraphitizable carbonaceous materials. The graphitizable carbonaceous material has a crystalline structure developed by heat treatment at a high temperature (for example, 2800 ° C. or higher), d ₀₀₂ decreases, and Lc
₍₀₀₂₎ increases and approaches those values of graphite. On the other hand, in the non-graphitizable carbonaceous material, the crystal structure does not develop so much even by the high temperature heat treatment. The carbonaceous material of the present invention is a non-graphitizable carbonaceous material, and its Lc ₍₀₀₂₎ is 15n.
m or less, preferably 10 nm or less, more preferably 5 n
m or less.

The carbonaceous material of the present invention has a ρ _B of 1.
It is preferably 70 g / cm ³ or less. For carbonaceous materials having almost the same d ₀₀₂ and Lc ₍₀₀₂₎ values, ρ _B
The fact that is small means that there are many fine pores. [rho _B is 1.70 g / cm ³ or less, preferably 1.65 g / cm ³ or less, more preferably 1.60 g /
It is not more than cm ³ .

The carbonaceous material of the present invention can be produced, for example, by the following method.

To a pitch such as petroleum pitch or coal pitch, an aromatic compound having 2 to 3 rings having a boiling point of 200 ° C. or more or a mixture thereof is added as an additive, heated and melt-mixed, and then molded into a pitch molded body. obtain. Then, the additive is extracted and removed from the pitch-molded product with a solvent having a low solubility in pitch and a high solubility in the additive, and the obtained porous pitch is oxidized, and then the pressure is reduced to 10 kPa or less. In 9
Baking is performed at a temperature of 00 ° C to 1500 ° C.

The purpose of the above-mentioned aromatic additive is to extract and remove the additive from the pitch molded product after molding to make the molded product porous and to control the fine structure of the resulting carbonaceous material and to It is to facilitate oxidation and baking. Such additives include, for example, naphthalene, methylnaphthalene,
One or two of phenylnaphthalene, benzylnaphthalene, methylanthracene, phenanthrene, biphenyl, etc.
It is selected from a mixture of two or more species. The amount of addition to the pitch is preferably in the range of 30 to 70 parts by weight with respect to 100 parts by weight of the pitch.

The pitch and the additives are mixed in a molten state by heating in order to achieve uniform mixing. The mixture of pitch and additive is preferably molded into particles having a particle size of 1 mm or less so that the additive can be easily extracted from the mixture. The molding may be performed in a molten state, or may be performed by a method such as pulverizing after cooling the mixture.

As a solvent for extracting and removing the additive from the mixture of pitch and the additive, aliphatic hydrocarbons such as butane, pentane, hexane, heptane, etc., mixtures mainly containing aliphatic hydrocarbons such as naphtha, kerosene, methanol, etc. And aliphatic alcohols such as ethanol, propanol and butanol are preferable.

By extracting the additive from the mixture of pitch and the additive molded body with such a solvent, the additive can be removed from the molded body while maintaining the shape of the molded body. At this time, it is presumed that voids of the additive are formed in the molded body and a pitch molded body having uniform porosity can be obtained.

Next, the thus obtained porous pitch molded body is oxidized. Oxidation is preferably at room temperature to 40
Perform at temperatures up to 0 ° C. As the oxidant, O ₂ ,
O ₃ , SO ₃ , NO ₂ , a mixed gas obtained by diluting these with air, nitrogen or the like, an oxidizing gas such as air, or an oxidizing liquid such as sulfuric acid, nitric acid or hydrogen peroxide solution can be used.

Oxidation of the porous pitch is conveniently carried out at 120 ° C. to 300 ° C. using a gas containing oxygen such as air or a mixed gas of air and another gas such as combustion gas as an oxidant. Yes, it is economically advantageous. In this case, if the softening point of the pitch is low, the pitch will be melted during oxidation and oxidation will be difficult. Therefore, the pitch used has a softening point of 1 or less.
It is preferably 50 ° C. or higher.

The degree of oxidation is preferably set so that the oxygen content by elemental analysis of the porous pitch after the oxidation treatment is 5 to 30% when the oxidation is performed using a gas containing oxygen. The oxygen content is preferably 10 to 25
%, And more preferably 13 to 22%.

In the method of the present invention, the heat treatment including the highest temperature experienced by the obtained carbonaceous material is called main firing.
In the main firing, the porous pitch after oxidation is set to 10 kPa (0.1
It is carried out at a temperature of 900 ° C to 1500 ° C under a reduced pressure of (atmospheric pressure) or less. In order to prevent the object to be fired from being oxidized during firing, it is preferable to perform firing in a reduced pressure atmosphere in which an oxidizing gas such as oxygen does not exist and only an inert gas such as nitrogen or argon is allowed. If the pressure under reduced pressure exceeds 10 kPa, it is not preferable because the decomposition gas is not sufficiently released from the material to be fired and the formation of fine pores is insufficient. The pressure is preferably 1 kPa or less, more preferably 0.1
It is kPa or less. If the main calcination temperature is lower than 900 ° C, carbonization of the material to be calcinated is insufficient, and when the obtained carbonaceous material is used as an electrode material of a secondary battery, the battery active material doped in the carbonaceous material is dedoped. The amount (irreversible capacity) that remains in the carbonaceous material without being increased becomes unfavorable.
Further, if the main calcination temperature exceeds 1500 ° C., ρ _H becomes small and the dope capacity of the obtained carbonaceous material of the battery active material decreases, which is not preferable. The main calcination is preferably 950 ° C to 1450 ° C, more preferably 1000 ° C to
Perform at 1400 ° C.

The firing can be carried out by continuously raising the pitch after oxidation to the final firing temperature (900 ° C. to 1500 ° C.), but once the temperature is lower than the final firing temperature. It is also possible to perform the main firing after performing the preliminary firing.

When a fine powdery carbonaceous material is required, the carbonaceous material obtained after the completion of the main firing can be crushed, but the pitch oxidized as described above (oxidized pitch ) Is calcined at 350 to 700 ° C. in an inert gas atmosphere (for example, in a gas atmosphere of nitrogen, argon or the like, or under reduced pressure) prior to the main calcination, and the volatile matter (measuring method described later) is 15% or less. The powdery carbonaceous material can be manufactured by obtaining the carbon precursor described above, pulverizing the carbon precursor to an average particle size of 100 μm or less, preferably 50 μm or less, and then firing the powder.

The volatile content of the carbon precursor is set to 15% or less in order to prevent melting of the crushed particles and fusion of the crushed particles during firing. The volatile content of the carbon precursor is preferably 10% or less.

Since the carbon precursor before the main calcination is much easier to pulverize and the abrasion of the crusher is less than that of the carbon precursor after the main calcination, the method of pulverizing the carbon precursor before the main calcination is very It is advantageous. Further, it is preferable to reduce the volatile content of the carbon precursor because the generation of tar and decomposition gas in the main firing step is reduced and the load of the main firing step is reduced.

The carbonaceous material of the present invention can also be produced by firing coconut shell char at a temperature of 900 ° C. to 1500 ° C. under a reduced pressure of 10 kPa or less.

In any of the above methods, the firing under reduced pressure may be performed throughout the firing process, but it is sufficient if the temperature range of 800 ° C. or higher is performed under reduced pressure.

In the case where the carbonaceous material of the present invention is used to form an electrode of a non-aqueous solvent type secondary battery, the carbonaceous material is made into fine particles having an average particle size of about 5 to 100 μm, if necessary.
Polyvinylidene fluoride, polytetrafluoroethylene,
A method of forming a layer having a thickness of, for example, 10 to 200 μm by bonding to a conductive current collector made of, for example, a circular or rectangular metal plate with a binder that is stable to a non-aqueous solvent such as polyethylene. The electrode is manufactured by. The preferable addition amount of the binder is 1 to 20% by weight with respect to the carbonaceous material.
Is. If the amount of the binder added is too large, the electric resistance of the obtained electrode increases, the internal resistance of the battery increases, and the battery characteristics deteriorate, which is not preferable. On the other hand, if the amount of the binder added is too small, the binding between the carbonaceous material particles and the current collector becomes insufficient, which is not preferable. The above is the value for a relatively small capacity secondary battery, but in order to form a larger secondary battery, a mixture of the carbonaceous fine particles and a binder is formed by a method such as press molding. It is also possible to manufacture a molded body having a larger thickness and electrically connect the molded body to a current collector.

The carbonaceous material of the present invention can be used as a positive electrode material of a non-aqueous solvent type secondary battery by utilizing its good doping property. However, as described above, the non-aqueous solvent type secondary battery can be used. It is preferably used for the constitution of a negative electrode of a secondary battery, particularly a negative electrode for doping lithium as a negative electrode active material of a lithium secondary battery.

In this case, the positive electrode material is LiCoO 2.
Complex metal chalcogenides such as ₂ , LiNiO ₂ and LiMnO ₄ are preferable, and they are formed with a suitable binder and a carbon material for imparting conductivity to the electrode to form a layer on the conductive current collector.

The non-aqueous solvent type electrolytic solution used in combination with the positive electrode and the negative electrode is generally formed by dissolving an electrolyte in a non-aqueous solvent. As the non-aqueous solvent, for example, one of organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane. Alternatively, two or more kinds can be used in combination. Further, as the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , L
iCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr,
_{LiB (C 6 H 5) 4} , LiN (So 2 CF 3) 2 or the like is used.

In a secondary battery, generally, the positive electrode layer and the negative electrode layer formed as described above are opposed to each other through a liquid-permeable separator made of a non-woven fabric or other porous material, if necessary. It is formed by immersing in.

The measurements of d ₀₀₂ , Lc ₍₀₀₂₎ ρ _B , ρ _H , H / C, and pitch volatiles and softening points of the carbon or graphitic materials described in this specification were conducted as follows. I went.

"Carbonaceous materials d ₀₀₂ and L
c ₍₀₀₂₎ ”: A carbonaceous material powder is filled in an aluminum sample cell, and CuKα rays (wavelength λ = 0.15418 nm) monochromated by a graphite monochromator are used as a radiation source, and X-rays are produced by a reflection defractometer method. Get the diffraction pattern. For correction of the diffraction pattern, corrections for Lorentz polarization factor, absorption factor, atomic scattering factor, etc. are not performed, and K
Rachinger only corrects the double line of α ₁ and K α _2.
It was performed by the method of. The peak position of the (002) diffraction line is obtained by the center of gravity method (the position of the center of gravity of the diffraction line is determined and the peak position is obtained from the corresponding 2θ value), and the (111) diffraction line of the high purity silicon powder for standard substance Was corrected, and d ₀₀₂ was calculated from the Bragg formula below.

Lc ₍₀₀₂₎ is the full width at half maximum of the (002) diffraction line of the carbonaceous sample and (11 of the high-purity silicon powder for standard substance).
1) β _1/2 was obtained from the half width of the diffraction line using the Alexander curve, and was calculated by the Scherrer's formula below. Here, the shape factor K is 0.9.

D ₀₀₂ = λ / (2 · sin θ) (Bragg's formula) Lc ₍₀₀₂₎ = K · λ / (β _1/2 cos θ) (Scherrer's formula) “ρ _B ”: defined in JIS R7212 According to the method, it was measured by the butanol method. The outline is given below.

Accurately measure the mass (m ₁ ) of a specific gravity bottle with a side tube having an internal volume of about 40 ml. Then, place about 10 samples on the bottom.
After putting it flat to a thickness of mm, its mass (m
₂ ) Weigh accurately. 1-Butanol is gently added to this to make a depth of about 20 mm from the bottom. Next, a light vibration is applied to the pycnometer to confirm that the generation of large bubbles has disappeared, and then the pycnometer is placed in a vacuum desiccator and gradually evacuated to 2.0 to 2.7 kPa. Keep that pressure for more than 20 minutes, take out after the bubble formation stops, fill it with 1-butanol, wipe it with a bottle of constant temperature water (30 ±
Soak for 15 minutes or more)
Align the liquid level of 1-butanol with the marked line. Next, this is taken out, the outside is well wiped off, and after cooling to room temperature, the mass (m ₄ ) is accurately measured.

Next, the same pycnometer was filled with 1-butanol alone, immersed in a constant temperature water bath in the same manner as above, the marked lines were set, and then the mass (m ₃ ) was measured.

Immediately before use, distilled water excluding dissolved gas by boiling is taken in a pycnometer, immersed in a constant temperature water bath as before, and the mass (m ₅ ) is measured after adjusting the marked lines.

Ρ _B is calculated by the following formula.

Ρ _B = (m ₂ −m ₁ ) (m ₃ −m ₁ ) d /
[{M ₂ −m ₁ − (m ₄ −m ₃ )} (m ₃ −m ₁ )] Here, d is the specific gravity of water at 30 ° C. (0.9946).

“Ρ _H ”: The measurement of ρ _H is made by Micromeritics Multivolume Pycnometer 130.
5, the sample was dried at 120 ° C. for 2 hours and then measured. The ambient temperature at the time of measurement was constant at 22 ° C. All the pressures in this measurement method are gauge pressures, which are absolute pressures minus ambient pressures.

The measuring device has a sample chamber and an expansion chamber, and the sample chamber has a pressure gauge for measuring the pressure inside the chamber. The sample chamber and the expansion chamber are connected by a connecting pipe equipped with a valve. A helium gas introduction pipe having a stop valve is connected to the sample chamber, and a helium gas delivery pipe having a stop valve is connected to the expansion chamber.

The measurement was performed as follows. The volume of the sample chamber (V _CELL ) and the volume of the expansion chamber (V _EXP ) are measured in advance using a standard sphere.

A sample is put in the sample chamber, and helium gas is caused to flow for 2 hours through the helium gas introduction pipe of the sample chamber, the connecting pipe, and the helium gas discharge pipe of the expansion chamber to replace the inside of the apparatus with the helium gas. Next, the valve between the sample chamber and the expansion chamber and the valve for the helium gas discharge pipe from the expansion chamber are closed (helium gas at the same pressure as the ambient pressure remains in the expansion chamber), and helium gas is introduced from the helium gas introduction pipe in the sample chamber. After introducing the gas to 134 kPa, the stop valve of the helium gas introducing pipe is closed. The pressure (P ₁ ) in the sample chamber is measured 5 minutes after the stop valve is closed. Next, the valve between the sample chamber and the expansion chamber is opened to transfer the helium gas to the expansion chamber, and the pressure (P ₂ ) at that time is measured.

The sample volume (V _SAMP ) is calculated by the following equation.

V _SAMP = V _CELL −V _EXP / [(P ₁ / P ₂ ) −1] Therefore, when the weight of the sample is W _SAMP , the density is ρ _H = W _SAMP / V _SAMP .

"H / C": determined by elemental analysis using a CHN analyzer.

"Volatile": Volatile is JIS R7212
The measurement was performed according to the method specified in. However, the sample was heated at 800 ° C. for 30 minutes.

"Softening point": Using a Shimadzu high-performance flow tester, 1 g of a sample ground to 250 μm or less was filled in a cylinder having a cross-sectional area of 1 cm ² having a nozzle of 1 mm in diameter at the bottom, and 9.8 N / cm ² (10 Kg / cm
^The temperature is raised at a rate of 6 ° C / min while adding the weight of ² ). As the temperature rises, the powder particles are softened and the filling rate is improved, and the volume of the sample powder decreases, but the volume stops decreasing above a certain temperature. When the temperature is further raised, the sample melts and flows out from the nozzle at the bottom of the cylinder. The temperature at which the volume reduction of the sample powder stops at this time is defined as the softening point of the sample. In the case of a sample having a high softening point, the sample may not flow out from the nozzle.

[0058]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 Petroleum pitch 6 having a softening point of 210 ° C., a quinoline insoluble content of 1% by weight and an H / C atomic ratio of 0.63.
8 kg and naphthalene 32 kg were placed in a pressure vessel having an inner volume of 300 liters equipped with a stirring blade, heated and melt-mixed at 190 ° C., then cooled to 80 to 90 ° C. and extruded to form a cord having a diameter of about 500 μm. A molded body was obtained. Next, this string-shaped molded product was crushed so that the ratio of diameter to length was about 1.5, and the crushed product was heated to 93 ° C. to give 0.53% by weight of polyvinyl alcohol (saponification degree: 88). %) Was poured into an aqueous solution in which it was dissolved, stirred and dispersed, and cooled to obtain a spherical pitch compact slurry. After removing most of the water by filtration, the naphthalene in the pitch molded body was extracted and removed with n-hexane in an amount about 6 times as much as the weight of the spherical pitch molded body. The porous spherical pitch thus obtained was heated to 260 ° C. while flowing heated air using a fluidized bed, and heated to 260 ° C.
It was held for a period of time to be oxidized to obtain a porous spherical oxidized pitch that is infusible to heat. The obtained oxidized pitch has an oxygen content of 1
It was 7% by weight. Next, the oxidized pitch was heated to 600 ° C. in a nitrogen gas atmosphere (normal pressure), held at 600 ° C. for 1 hour, and calcined to obtain a carbon precursor having a volatile content of 2% or less. The obtained carbon precursor was pulverized to obtain a powdery carbon precursor having an average particle diameter of 25 μm. Next, the powdery carbon precursor was charged into a vacuum firing furnace, and the inside was replaced with nitrogen. The temperature was raised while introducing a small amount of nitrogen into the vacuum firing furnace, and when it reached 800 ° C., suction was performed with a vacuum pump, and the pressure in the vacuum firing furnace was adjusted to 0.01 to 0.
It was kept at 03 Pa. When the temperature of the vacuum firing furnace reached 1200 ° C., the temperature was further raised and the temperature was maintained at 1200 ° C. for 1 hour to carry out main firing, followed by cooling to produce a powdery carbonaceous material.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

Example 2 A porous carbonaceous material was prepared in the same manner as in Example 1 except that the oxidation temperature of the porous spherical pitch in Example 1 was 200 ° C. and the oxygen content of the oxidized pitch was 10% by weight. Was manufactured.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

(Examples 3 and 4) Main firing temperatures in Example 1 were 1000 ° C. (Example 3) and 1250, respectively.
A carbonaceous material was produced in the same manner as in Example 1 except that the temperature was changed to ° C (Example 4).

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

(Examples 5 and 6) The pressure in the furnace during the main firing in Example 1 was 40 Pa (Example 5) and 40 Pa, respectively.
A carbonaceous material was produced in the same manner as in Example 1 except that the pressure was changed to 00 Pa (Example 6).

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

(Example 7) Palm shell char (MC sea
Carbon Co., Ltd. 60 in a nitrogen gas atmosphere (normal pressure)
The temperature is raised to 0 ° C., the temperature is kept at 600 ° C. for 1 hour, and the calcination is performed.
A carbon precursor having a volatile content of 2% or less was obtained. The obtained carbon precursor was pulverized to obtain a powdery carbon precursor having an average particle diameter of 25 μm. The powdery carbon precursor was charged into a vacuum firing furnace, and the inside was replaced with nitrogen. The temperature was raised while introducing a small amount of nitrogen into the vacuum firing furnace, and when it reached 800 ° C., it was sucked with a vacuum pump to keep the pressure in the vacuum firing furnace at 0.01 to 0.03 Pa. The temperature of the vacuum firing furnace is 1200 ℃
When the temperature reaches 1, the temperature is maintained at 1200 ° C. for 1 hour to perform the main calcination, followed by cooling to produce a powdery carbonaceous material.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

Example 8 A carbonaceous material was produced in the same manner as in Example 7 except that the main firing temperature in Example 7 was changed to 1300 ° C.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

Comparative Example 1 The petroleum pitch used in Example 1 was crushed to a particle size of 20 μm or less. This crushing pitch 20
0 g was charged into a glass eggplant-shaped flask having protrusions inside with an internal volume of 1 liter, and while the eggplant-shaped flask was tilted and rotated, air was flowed at 1 liter / min.
The temperature was raised to 100 ° C. at a heating rate of 100 ° C./hour, and held at 300 ° C. for 1 hour for oxidation. The obtained oxidized pitch had an oxygen content of 10% by weight. This oxide pitch was charged into a vacuum firing furnace and the pressure in the vacuum firing furnace was adjusted to 0.01 to 0.03P.
While maintaining at a, the temperature was raised to 1200 ° C. at a temperature rising rate of 5 ° C./minute, and the temperature was maintained at 1200 ° C. for 1 hour to carry out main firing to obtain a carbonaceous material.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

Comparative Example 2 A carbonaceous material was produced in the same manner as in Example 1 except that the main calcination was carried out under a reduced pressure of 40 kPa.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

Comparative Example 3 The petroleum pitch described in Example 1 was oxidized at 600 ° C. in a nitrogen gas atmosphere (normal pressure) without being oxidized.
After calcination for 1 hour, the powder was pulverized to obtain carbon precursor fine particles having an average particle diameter of about 20 μm.

Then, the carbon precursor particles are added in an amount of 0.01 to
Carbonization was performed at 1200 ° C. for 1 hour under reduced pressure of 0.03 Pa to obtain a carbonaceous material.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

Reference Example and Comparative Example 4 A carbonaceous material was produced in the same manner as in Example 1 except that the main firing temperatures were 800 ° C. (reference example) and 1600 ° C. (comparative example 4), respectively.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

Comparative Example 5 Furfuryl alcohol 100
85% phosphoric acid 0.5g and water 10.0g are added to g, and the temperature is 90 ° C.
After reacting for 5 hours at room temperature, 1N NaOH aqueous solution is gradually added to adjust the pH to about 5, and further 2.7 kP
Residual water and unreacted alcohol were distilled off under the reduced pressure of 70 ° C. at 70 ° C. to obtain a furfuryl alcohol initial condensation product.
The obtained condensate was further cured at 150 ° C. for 16 hours to obtain a furan resin.

Next, the obtained furan resin was roughly crushed and then calcined for 1 hour at 500 ° C. under a nitrogen stream (normal pressure). After crushing this to an average particle size of about 20 μm, it was carbonized at 1100 ° C. for 1 hour in a nitrogen gas atmosphere (normal pressure) to obtain a carbonaceous material.

Properties of the obtained carbonaceous material are shown in Table 1 below.

Comparative Example 6 Orthocresol 108 g, paraformaldehyde 32 g and ethyl cellosolve 242
g and 10 g of sulfuric acid were added and reacted at 115 ° C. for 3 hours, and then 17 g of sodium hydrogen carbonate and 30 g of water were added to neutralize the reaction solution. The resulting reaction solution was poured into 2 liters of water stirred at high speed to obtain a novolak resin. Next, 17.3 g of novolac resin and 2.0 g of hexamine were kneaded at 120 ° C., and heated at 250 ° C. for 2 hours in a nitrogen gas atmosphere to obtain a cured resin. The obtained cured resin was coarsely pulverized, calcined at 600 ° C. in a nitrogen atmosphere (normal pressure) for 1 hour, and further heat-treated at 1900 ° C. in an argon gas atmosphere (normal pressure) for 1 hour to obtain a carbonaceous material. . The obtained carbonaceous material was further pulverized to have an average particle size of 15 μm.

The characteristics of the obtained carbonaceous material are shown in Table 1 below.

(Comparative Example 7) Evaluation was carried out using scaly natural graphite (CP from Nippon Graphite Co., Ltd.) produced in Madagascar. This natural graphite has a fixed carbon content of 97%, an ash content of 2%, a volatile content of 1%, and an average particle size of 7 μm.

The properties of this natural graphite are shown in Table 1 below.

(Doping / Undoping Test of Active Material) Using the carbonaceous materials obtained in the above Examples and Comparative Examples, a non-aqueous solvent type secondary battery was prepared as follows, and its characteristics were evaluated. evaluated.

The carbonaceous material of the present invention is suitable for use as the negative electrode of a non-aqueous solvent secondary battery. However, the effect of the present invention is to improve the doping capacity, de-doping capacity and carbon content of a carbon material without de-doping. The amount remaining in the quality material (irreversible capacity)
A lithium secondary battery in which a large excess of lithium metal with stable characteristics is used as the counter electrode (negative electrode) and the carbonaceous material obtained above is used as the positive electrode for accurate evaluation without being affected by variations in the performance of the counter electrode. Was constructed and its characteristics were evaluated.

That is, the positive electrode (carbonaceous material electrode) was manufactured as follows. After 90 parts by weight of the particulate carbonaceous material and 10 parts by weight of polyvinylidene fluoride produced as described above, N-methyl-2-pyrrolidone was added to form a paste, which was evenly applied on a copper foil and dried. Then, peel it off from the copper foil and punch it into a disk shape with a diameter of 21 mm. This was pressed against a stainless steel mesh disk having a diameter of 21 mm by a press to be a pressure-bonded positive electrode. The amount of carbon material in the positive electrode was adjusted to about 40 mg.

As the negative electrode, a metal lithium thin plate having a thickness of 1 mm punched into a disk shape having a diameter of 21 mm was used.

Using the positive electrode and the negative electrode thus produced, as the electrolytic solution, LiClO ₄ was added at a ratio of 1 mol / liter to a mixed solvent in which propylene carbonate and dimethoxyethane were mixed at a volume ratio of 1: 1. Was used to form a non-aqueous solvent type lithium secondary battery using a polypropylene microporous membrane as a separator.

In the lithium secondary battery having such a structure, the carbonaceous material was doped with lithium and dedoped to obtain the capacity at that time.

Doping was carried out by repeating an operation in which a current was applied for 1 hour at a current density of 0.5 mA / cm ² and then rested for 2 hours until the equilibrium potential between terminals reached 5 mV. The value obtained by dividing the quantity of electricity at this time by the weight of the carbonaceous material used was defined as the dope capacity and expressed in units of mAh / g.
Next, in the same manner, an electric current was applied in the opposite direction to dedope the lithium doped in the carbonaceous material. Dedoping is 0.5m
The operation of supplying current for 1 hour at a current density of A / cm ² and then resting for 2 hours was repeated, and the terminal voltage of 1.5 V was taken as the cutoff voltage. The value obtained by dividing the amount of electricity flowing at this time by the weight of the carbonaceous material used was defined as the dedoping capacity, and was defined as mAh / g.
It was expressed in units. Then, the irreversible capacity was determined as the difference between the doping capacity and the dedoping capacity. The value obtained by dividing the dedoping capacity by the doping capacity was multiplied by 100 to obtain the discharge efficiency (%). This is a value indicating how effectively the active material was used.

Table 2 shows the battery characteristics of the lithium secondary battery in which each carbonaceous material obtained as described above is used as a positive electrode.

From Table 2, the secondary batteries using the carbonaceous materials obtained in the examples of the present invention are comparative examples 1, 2, 3, 4,
It can be seen that the dope and dedope capacities are both large as compared with the battery using the carbon materials obtained in 5 and 6.

The carbon material obtained in the reference example has a large lithium doping and dedoping capacity and is suitable as a carbonaceous material for a high energy density secondary battery. However, the amount of remaining lithium is large, and lithium is not effectively used.

In the secondary battery using the natural graphite of Comparative Example 7, lithium could not be doped due to decomposition of the electrolytic solution.

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[Table 1]

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[Table 2]

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As described above, according to the present invention, the carbonaceous material for a non-aqueous solvent secondary battery having a large capacity for doping and dedoping of a battery active material by controlling the fine structure of the carbonaceous material. Will be provided. Then, by using this carbonaceous material to form a negative electrode of a lithium secondary battery, for example, a secondary battery having a high utilization rate of lithium and a high energy density can be manufactured.

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Claims (4)

(57) [Claims] 1. The average layer spacing of (002) planes determined by X-ray diffractometry is 0.365 nm or more, and the density (ρ _B ) measured with butanol as a substitution medium is compared with the density (ρ) measured with helium gas as a substitution medium. _H ) ratio (ρ _H /
ρ _B ) is 1.25 or more , a carbonaceous material for secondary battery electrodes. 2. The atomic ratio (H / C) of hydrogen to carbon is 0.1.
It is the following, The carbonaceous material for secondary battery electrodes of Claim 1. 3. A petroleum-based or coal-based pitch is added with one or more two or three ring aromatic compounds having a boiling point of 200 ° C. or higher as an additive, heated, melted and mixed, and then molded. To obtain a pitch compact, and then extract and remove the additive from the pitch compact with a solvent having a low solubility in the pitch and a high solubility in the additive, and oxidizing the obtained porous pitch. Then, 900 ° C under reduced pressure of 10 kPa or less
A method for manufacturing a carbonaceous material for a secondary battery electrode, which comprises firing at a temperature of ˜1500 ° C. 4. The method for producing a carbonaceous material for a secondary battery electrode according to claim 3, wherein the porous pitch is oxidized with a gas containing oxygen.