JP3091943B2 - Method for producing carbon particles for negative electrode of non-aqueous secondary battery and carbon particles obtained by the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for a non-aqueous secondary battery.
Method for producing carbon particles and carbon obtained by the method
Regarding particles .

[0002]

2. Description of the Related Art In recent years, lithium ion secondary batteries have attracted attention as a power source required for portable electronic devices because they are small and lightweight high energy storage batteries. The energy density indicating the battery performance depends on the degree of doping (occluding) lithium ions in the carbonaceous material as the negative electrode active material.

[0003] The positive electrode active material, generally Li _x M _y O _z (M is one or more metal elements mainly containing a transition metal,
0.5 ≦ x ≦ 2, 1 ≦ y ≦ 2, 2 ≦ z ≦ 4), which releases lithium ions at the time of charging, is doped (charged) into the carbonaceous material of the negative electrode, and carbonized at the time of discharging. Lithium ions are dedoped (discharged) from the porous material. It is desirable that the carbonaceous material of the negative electrode has a higher specific gravity because filling a limited internal volume of the battery can with more active material leads to an increase in the capacity of the battery. Also, the ratio of the amount of undoping electricity to the amount of doping electricity,
That is, it is desirable that the current efficiency be approximately 100% because lithium of the positive electrode is not consumed except for charging and discharging.
It is preferable that the current efficiency during the first charging is as high as possible. Heat-treated petroleum pitch coke and coal pitch coke particles are commonly used as the carbonaceous material for the negative electrode, but batteries with higher capacities have emerged as power sources for various electronic and electrical devices. It has been long-awaited and various studies have been made.

[0004] For example, mesophase pitch microspheres (spherulites generated when pitches are heat-treated) are made into 2300 to 30
It has been proposed to use graphitized mesophase pitch microspheres obtained by heat treatment at 00 ° C. at a high temperature as a negative electrode active material. Although the graphitized mesophase pitch spheres can obtain a higher electric capacity than pitch coke, lithium easily precipitates on the particle surface, and has a problem in battery safety such as lithium dendrite short.

In order to obtain a sphere required for forming a negative electrode,
800-1 for mesophase pitch small spheres by oxygen
Heat treatment at 500 ° C. to burn off and remove the binder attached to the surface layer of the small sphere, It was necessary to perform complicated control to suppress the noise. Also, the graphitized mesophase pitch spheres have the disadvantage that the negative voltage as the negative electrode is higher than the pitch coke, which represents the voltage drop at the start of discharge at a constant current. In addition, the pulverized lump obtained by simply heat-treating at 800 to 1500 ° C. has only an electric capacity equivalent to that of ordinary pitch coke.

[0006]

Therefore , the present invention has a high electric capacity, is excellent in safety , and further has an overvoltage.
Made in suitable carbon particles smaller nonaqueous negative electrode for a secondary battery
An object of the present invention is to provide a production method and carbon particles obtained by the method .

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and have found that
Green mesophase pipe obtained from coal tar pitch
After the surface treatment of the fine spheres or the mixture with the graphite powder mainly composed of the spheres with an oxygen-containing organic material,
The amorphous carbon particles obtained by heat treatment at 〜1300 ° C. have been found to be extremely effective in achieving the above object, and the present invention has been completed.

That is, the present invention provides a green mesophase
Pitch small spheres or graphite powder mainly composed of the small spheres
One of the surfaces of the mixture with the powder is coated with an oxygen-containing organic substance.
After covering, heat treatment at a temperature of 800 to 1300 ° C
Of carbon particles for non-aqueous secondary battery negative electrode characterized by the following
Method (1). In another invention, the oxygen-containing organic substance is hard.
Phenolic resin, furan resin, furfuryl alcohol
At least one selected from the group consisting of starch, starch and sucrose.
For producing carbon particles for negative electrode of non-aqueous secondary battery (2)
It is. Still another invention is described in the above (1) or (2).
The average particle diameter obtained by the manufacturing method described above is 60 μm or less.
Below, and the carbon interlayer distance (d ₀₀₂ ) is 0.370-0.
350 nm, the crystallite thickness (Lc) in the C-axis direction is 0.8
Non-aqueous secondary having a specific gravity of 1.7 to 2.1 nm and a specific gravity of 1.7 to 2.1
It is a carbon particle (3) for battery negative electrodes .

Hereinafter, the present invention will be described in detail. Green mesophase pitch globules used in the present invention (hereinafter, sometimes simply referred to as microspheres) is to have a lamellar structure of the carbon layer (a kind of layered structure), caking material on the surface layer
Having a high quality and volatile matter , for example, petroleum tar pitch, coal tar pitch at 300 to 500 ° C.
The mesophase pitch small spheres generated when heated in is added to a solvent such as tar or oil, and the small spheres are separated by a centrifugation method or the like, and if necessary, the remaining solvent is volatilized at 250 to 500 ° C. And partially cross-linked.
The small spheres obtained here have a toluene insoluble content of 85-9.
8% by weight, quinoline soluble matter 15-5% by weight, volatile matter (8
6 to 14% by weight)
The average particle size is 1 to 30 μm,
Preferably it is 3 to 15 μm. In addition, here
The small spheres are green mesophase pitch spheres.
And a crushed mass formed by fusion.

The oxygen-containing organic substance used in the present invention is not particularly limited as long as it has fixed carbon after heat treatment. Examples of such an oxygen-containing organic substance include a curable phenol. Resins ( curable novolak type, resol type, benzylic ether type), furan resin, furfuryl alcohol, melamine resin, urea resin, epoxy resin, polyimide resin, unsaturated polyester resin, polyurethane resin, starch, sucrose, cellulose, Examples include carboxymethyl cellulose, polyvinyl alcohol, partially saponified polyvinyl acetate, polyalkylene oxides such as polyethylene oxide and polypropylene oxide, and acrylate and methacrylate derivatives thereof. Among them, curable <br/> phenolic resin, furan resin, furfuryl alcohol,
Starch and sucrose are preferred because they have high fixed carbon.
Particularly preferred are curable phenolic resins. These may be used alone or in combination of two or more. The amount of the oxygen-containing organic substance to be used is not particularly limited, but is generally 3% by weight or more in terms of solid content based on the green mesophase spherules or the mixture thereof with graphite. However, considering workability at the time of coating treatment or heat treatment, the content is preferably 5 to 50% by weight. Such an oxygen-containing organic substance can be used in combination with other additives such as tar pitch and powdered coke as needed.

The carbon particles according to the present invention are obtained, for example, by treating the surface of the green mesophase pitch small spheres or a mixture of the small spheres with graphite powder with an oxygen-containing organic substance and removing water or a solvent by heating. By performing heat treatment under an inert gas atmosphere, oxygen-containing organic substances (especially curable phenolic resin) and caking substances and residual volatile components in the surface layer of the small spheres are repeatedly fused and separated to form small spheres (spheres). It is produced as amorphous particles that do not retain the original shape of the body). In particular, in order to obtain carbon particles suitable for a negative electrode for a non-aqueous secondary battery, the heat treatment temperature should be 800 to 1300.
° C, particularly preferably 900 to 1200 ° C. The reason is that if the temperature is lower than 800 ° C., the initial current efficiency is remarkably lowered, which is not preferable. When the temperature exceeds 1300 ° C,
This is because the amount of discharge electricity is almost the same as that of the heat treatment product of the green mesophase pitch small spheres alone. Among such carbon particles, the average particle diameter is 60 μm or less, the carbon interlayer distance (d ₀₀₂ ) is 0.370 to 0.350 nm, the crystallite thickness in the C-axis direction (Lc) is 0.8 to 10 nm, It is preferable that the true specific gravity is in the range of 1.7 to 2.1, particularly 1.8 to 2.1, so that a large electric capacity can be realized and an overvoltage can be reduced. In addition,
The graphite powder is suitably used in the production of carbon particles for a negative electrode, and is usually used by being mixed with small spheres as described above or is used by being previously mixed with an oxygen-containing organic substance. You may mix and use with the processed small sphere. The compounding amount is usually 0.1% by weight or more based on the small spheres, and preferably 5 to 10% by weight from the viewpoint of battery safety. In the production of the carbon particles of the present invention, since the surface of the small spheres is treated with an oxygen-containing organic substance, a conventional pretreatment for removing the caking substance on the surface layer of the small spheres, for example, by a low-temperature heat treatment It is not necessary to perform a complicated control of controlling the fusibility by performing a crosslinking treatment, an oxidative crosslinking treatment with oxygen, or the like.

[0012] More specifically, such carbon particles are composed of the small spheres (preferably a mixture with graphite powder mainly composed of the small spheres), the oxygen-containing organic substance, and the tar pitch optionally added. Kneading machine capable of stirring and mixing additives such as, for example, a heating type kneader, and then, for example, the thing subjected to stirring and mixing processing to a temperature of 120 to 180 ° C. is transferred to a heat treatment furnace, and an atmosphere in which oxidation is unlikely to occur. For example, under an atmosphere of nitrogen, argon, or the like, from an ordinary temperature to 500 ° C., a heat treatment is performed at a temperature increasing rate appropriately selected from the range of 0.05 to 0.5 ° C./min. The temperature up to the temperature can be obtained by performing a heat treatment at a heating rate appropriately selected from the range of 0.05 to 10 ° C./min. At this time, it is preferable to use an oxygen-containing organic substance which is difficult to be heated and melted in advance as an aqueous solution or an organic solvent solution.

The negative electrode for a non-aqueous secondary battery according to the present invention is characterized in that the carbon particles and a binder such as carboxymethyl cellulose, fluororubber, polyvinylidene fluoride, polyvinylpyridine, polyvinyl alcohol, polyacrylate, EPDM rubber, diene Dispersion with system rubber, etc.
For example, it is obtained by coating, drying and pressing on a current collector such as a metal foil, mesh, or porous body of copper, stainless steel or nickel having a thickness of 1 to 50 μm.

In the non-aqueous secondary battery according to the present invention,
The positive electrode may be, for example, Li _x
Co _y M _z O ₂ (however, M is Al, In, Sn, Mn,
At least one selected from Fe, Ti, Zr, and Ce
X, y, z are each 0 <x ≦ 1.1,
0.5 <y ≦ 1, representing the number of z ≦ 0.15), Li _x C
oO ₂ (0 <x ≦ 1), Li _x Co _y Ni _z O ₂ (0 <x ≦
1, y + z = 1), as lithium nickel oxide, for example, Li _x NiO ₂ (0 <x ≦ 1), Li _x Ni _y M _z O
₂ (where M represents at least one metal selected from Mn, Ti and Fe, x and z are each 0 <x ≦ 1,
0.1 <z ≦ 0.3), and examples of the lithium manganese oxide include LiMnO ₃ and Li _x MnO ₂ (0 <
x ≦ 1), Li _x Mn ₂ O ₄ (0 <x <2), LiCo _x M
n _2-x O ₄ (0 <x ≦ 0.5), Li _x Mn _{2- y My} O ₄ (where M is at least one metal selected from Ni, Co, Ti, Fe) Where x and y are each 0.5 ≦ x ≦
2, 0.1 <y ≦ 0.2), and the electrolyte is, for example, LiClO ₄ , LiAsF ₆ , LiPF ₆ , L
iBF ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ S
Any one or a mixture of two or more lithium salts such as O ₂ ) ₂ NLi, and the solvent is, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane,
2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-
Dioxolan, sulfolane, methylsulfolane, acetonitrile, propionitrile, methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, hexyl acetate, methyl propionate, ethyl propionate, butyl propionate, hexyl propionate, triethyl phosphate , Triethylhexyl phosphate, trilaurel phosphate or the like, or a mixture of two or more thereof, and the separator is a single membrane of a polyolefin microporous membrane such as polyethylene or polypropylene, or one or two of them.
It refers to one or more kinds of bonded films and those using a carbonaceous material as an active material as a negative electrode.

The negative electrode for a non-aqueous secondary battery of the present invention may be used as it is with the above-described positive electrode, electrolytic solution and separator, and may be doped with lithium ions from the positive electrode at the time of initial charging, or may be converted into lithium metal in advance. , Lithium alloy or lithium iodide for doping in advance.

[0016]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. (Measurement method) The current efficiency (%) is the amount of discharged electricity / the amount of charged electricity × 100.
Expressed by The discharge capacity (mAh / g) of the negative electrode active material is determined as the amount of discharge electricity per weight of the active material. The capacity retention (%) is a percentage of a discharge capacity ratio (current efficiency) in five cycles with respect to the first discharge capacity. Lamination thickness Lc (nm) of carbon mesh plane in C-axis direction, spacing d between carbon mesh planes
₀₀₂ (nm) is calculated by an X-ray diffraction method according to the “Japan Society for the Promotion of Science”. In addition, it calculates excluding the peak of the added graphite. The true specific gravity is JIS K215
Measure according to the method of 1. Preparation of Negative Electrode for Nonaqueous Secondary Battery Based on 100 parts by weight of carbon particles obtained in Examples and Comparative Examples, 0.8 parts by weight of carboxymethyl cellulose as a binder and 2.0 parts of crosslinked rubber latex particles of styrene-butadiene were used. 100 parts by weight of an aqueous solution consisting of parts by weight is added to form a dispersion, which is coated on one surface of an electrolytic copper foil having a thickness of 18 μm, dried, and pressed by compression. Using this as a working electrode, a lithium sheet pressed against a stainless steel net through a polyethylene microporous membrane was used as a counter electrode, and a volume fraction of 1.0 mol of LiBF ₄ propylene carbonate 25%, ethylene carbonate 25%, and γ-butyrolactone 50% was used. Charge is started at a maximum current density of 1.0 mA / cm ^{2 in} a mixed solvent at a rate of 10% and then charged for 8 hours. Vs. Li / Li +
Doping (charging) to a potential of 10 mV. Discharge is performed up to Li / Li + potential of 1.0 V to determine discharge capacity.
Expressed in mAh / g as the amount of discharge electricity per weight of active material. The overvoltage (V) is obtained by measuring a voltage drop at the moment of starting discharge at a constant current of 1.0 mA / cm ² .

Example 1 100 parts by weight of coal-based green mesophase pitch microspheres (average particle size: 12 μm, toluene insoluble content: 97% by weight, quinoline soluble content: 9% by weight, volatile content: 11% by weight) and liquid resol type 30 parts by weight of a phenolic resin (solid content) and 6 parts by weight of graphite powder were charged into a heating kneader and mixed.
After mixing and heat treatment to 0 ° C, the mixture is transferred to an electric furnace, and from room temperature to 500 ° C in a nitrogen atmosphere, at a rate of 0.2 ° C / minute, 500 to 9 ° C.
Heat treatment was performed at a heating rate of 2 ° C./min up to 00 ° C. to obtain carbon particles for preparing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

Example 2 100 parts by weight of petroleum-based green mesophase pitch microspheres (average particle diameter: 10 μm, toluene insoluble content: 98% by weight, quinoline soluble content: 8% by weight, volatile content: 10% by weight), and graphite powder 5 1 part by weight and 30 parts by weight of a curable novolak type phenol resin were put into a heating kneader, and
After mixing and heating to 50 ° C., the mixture is transferred to an electric furnace, and from room temperature to 500 ° C. in a nitrogen atmosphere at 0.2 ° C./min,
Heat treatment was performed at a heating rate of 2 ° C./min up to 900 ° C. to obtain carbon particles for producing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

Example 3 100 parts by weight of coal-based green mesophase pitch microspheres (average particle diameter 15 μm, toluene insoluble matter 97% by weight, quinoline soluble matter 9% by weight, volatile matter 11% by weight) and liquid resol type 15 parts by weight of a phenolic resin (solid content) and 30 parts by weight of a coal-based pitch are charged into a heating kneader, and 160
After mixing and heating to 500 ° C., the mixture is transferred to an electric furnace, and from room temperature to 500 ° C. in a nitrogen atmosphere at a rate of 0.2 ° C./min.
2 ° C / min up to 0 ° C, 5 ° C / min up to 900-1200 ° C
Heat treatment was performed at an elevated temperature for one minute to obtain carbon particles for producing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

Example 4 100 parts by weight of the same coal-based green mesophase pitch spheres as in Example 1 described above, 5 parts by weight of graphite powder, and 10 parts by weight of a liquid resol type phenol resin (solid content) were heated. The mixture was put into a kneader and mixed and heat-treated to 160 ° C.
0.2 ° C / min up to 0 ° C, 2 ° C up to 500-900 ° C
Heat treatment was performed at a temperature increase rate of 5 ° C./min from 900 to 1100 ° C./min to obtain carbon particles for producing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

Comparative Example 1 The same petroleum-based green mesophase pitch spheres as in Example 2 described above were used alone in an electric furnace under a nitrogen atmosphere from room temperature to 500 ° C. at a rate of 0.2 ° C./min. Heat treatment was performed at a temperature increase rate of 2 ° C./min up to the temperature of 2 ° C./minute, and sintering was performed. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

Comparative Example 2 The same petroleum green mesophase pitch spheres as in Example 2 were extracted with quinoline, and the temperature was raised from room temperature to 1000 ° C. in an electric furnace under a nitrogen atmosphere by 0.2 ° C./min. Heat treatment was performed at a temperature to obtain carbon particles for producing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

Comparative Example 3 Coal-based green mesophase pitch spheres treated with the same curable phenolic resin as in Example 1 were heated at a rate of 0.2 ° C./min. 50
Heat treatment was performed at a temperature increase rate of 2 ° C./min from 0 to 750 ° C. to obtain carbon particles for producing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

(Comparative Example 4) A curable phenol resin alone was heated from room temperature to 500 ° C. in a nitrogen atmosphere at a rate of 0.2 ° C./min from room temperature to 500 ° C. in a nitrogen atmosphere. After further holding for 30 minutes, this was crushed to obtain carbon particles for producing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the same.
Shown in

Comparative Example 5 The same composition as in Example 1 was heat-treated under the same temperature conditions.
Heat treatment was performed from 900 ° C. to 1350 ° C. at a temperature increase rate of 2 ° C./min to obtain carbon particles for producing a negative electrode for a non-aqueous secondary battery. Table 1 shows the characteristics of the obtained carbon particles and the evaluation results of the negative electrode manufactured using the carbon particles.

Comparative Example 6 Table 1 shows the characteristics of a conventional petroleum pitch coke (needle coke) and the evaluation results of a negative electrode produced using the same.

As shown in Table 1, in Examples 1 to 4 according to the present invention, the initial discharge capacity was compared with that of the conventional petroleum pitch coke of Comparative Example 6, as shown in Table 1. And 133-196%, which is extremely large,
The current efficiency at the fifth cycle, which is the capacity retention rate, is 10
0%, and the overvoltage is equal to or less than the conventional example. However, if the heat treatment temperature is lower than 800 ° C., the initial current efficiency is significantly reduced, which is not preferable. On the other hand, when the temperature exceeds 1300 ° C., the amount of discharge electricity is almost the same as that of the heat-treated green mesophase pitch sphere alone.

[0028]

[Table 1]

[0029]

According to the present invention, green mesophase pitch microspheres or graphite powder mainly composed of the microspheres
The mixture with the powder is subjected to a surface treatment with an oxygen-containing organic substance such as a curable phenol resin and the like.
The carbon particles obtained by performing the heat treatment at 1300 ° C., preferably 900-1200 ° C., have a relatively high true specific gravity, and when used as a negative electrode active material, are compared with the conventional petroleum-based pitch coke. 133-196%, and a high specific discharge electricity amount, and the capacity retention rate is good.
It is possible to provide a negative electrode for a non-aqueous secondary battery which is excellent in safety and has a small overvoltage.

Continuation of front page (56) References JP-A-5-283060 (JP, A) JP-A-5-307959 (JP, A) JP-A-5-174820 (JP, A) JP-A-7-302594 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 C04B 41/85 C04B 35/52

Claims (3)

(57) [Claims] 1. A green mesophase pitch small sphere or
A mixture of the small spheres with a graphite powder
After coating one of the surfaces with an oxygen-containing organic substance,
Non-aqueous, characterized by heat treatment at a temperature of 1300C
Of producing carbon particles for a negative electrode of a secondary battery. 2. An oxygen-containing organic substance comprising a curable phenol resin,
Group of furan resin, furfuryl alcohol, starch and sucrose
The non-woven fabric according to claim 1, which is at least one member selected from the group consisting of:
A method for producing carbon particles for a negative electrode of an aqueous secondary battery. 3. The method according to claim 1, wherein
The obtained carbon particles having an average particle diameter of 60 μm
The distance between carbon layers (d ₀₀₂ ) is 0.370-
0.350 nm, the crystallite thickness (Lc) in the C-axis direction is
0.8 to 10 nm, true specific gravity of 1.7 to 2.1
Carbon particles for a negative electrode of a non-aqueous secondary battery, characterized in that: