JPH07302594A - Carbonaceous particles and negative electrode for lithium ion secondary battery using the same - Google Patents

Abstract

(57) [Summary] [Object] To provide a carbonaceous particle having a high electric capacity and excellent in safety and suitable for a negative electrode for a lithium ion secondary battery, and a negative electrode for a lithium ion secondary battery having a small overvoltage. [Composition] An oxygen-containing organic substance is adhered to the surface of the pulverized green coke of mesophase pitch and heat-treated to have an average particle diameter of 60 μm or less and a carbon interlayer distance (d ₀₀₂ ) of 0.37.
0 to 0.350 nm, thickness of crystallite in the C-axis direction (Lc)
Is 0.8 to 10 nm and the true specific gravity is in the range of 1.7 to 2.1, and the carbonaceous particles are suitable for a negative electrode for a lithium ion secondary battery. Further, the carbonaceous particles are used as an active material of a negative electrode for a lithium ion secondary battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbonaceous particles and a negative electrode for a non-aqueous secondary battery using the same, and more particularly to a negative electrode for a lithium ion secondary battery having a high electric capacity.

[0002]

2. Description of the Related Art In recent years, a lithium ion secondary battery has been attracting attention as a power source for portable electronic devices because it is a compact and lightweight high energy storage battery. The energy density indicating the battery performance depends on the degree of doping (storage) of lithium ions in the carbonaceous material that is the negative electrode active material.

The positive electrode active material is 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 emits lithium ions during charging, is doped (charged) into the carbonaceous material of the negative electrode, and is discharged during discharge. Ions are dedoped (discharged) from the quality material. It is desirable for the carbonaceous material of the negative electrode to have a higher specific gravity because filling the limited inner volume of the battery can with more active material leads to higher capacity of the battery. Also, the ratio of the dedoping electric quantity to the doping electric quantity,
That is, it is desirable that the current efficiency be almost 100% because the positive electrode lithium is not consumed except for charging and discharging, and it is also preferable that the current efficiency at the first charging is as high as possible. Particles of heat-treated petroleum pitch coke and coal pitch coke are usually used as the carbonaceous material of this negative electrode, but the emergence of batteries with higher capacities as power sources for various electronic and electrical devices has emerged. The long-awaited and various studies have been made.

For example, 2300 to 30 mesophase pitch small spheres (spherulites generated when heat-treating pitches) are used.
It has been proposed to use graphitized mesophase pitch globule obtained by high temperature heat treatment at 00 ° C. as a negative electrode active material. Although this graphitized mesophase pitch small sphere can obtain a higher electric capacity than pitch coke, lithium is likely to be deposited on the particle surface, and there is a problem in battery safety such as lithium dendrite short circuit.

Further, the graphitized mesophase pitch microspheres are
As a negative electrode, there was a drawback that the overvoltage, which represents a voltage drop at the moment of starting discharge at a constant current, was larger than that of pitch coke.

[0006]

SUMMARY OF THE INVENTION Therefore, it is a first object of the present invention to provide carbonaceous particles having a high electric capacity and excellent safety, which are suitable for a negative electrode for a lithium ion secondary battery. . And the 2nd object of this invention is to provide the negative electrode for lithium ion secondary batteries which uses this carbonaceous particle and whose overvoltage is small.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that petroleum tar pitch,
A green coke pulverized product of mesophase pitch, which is obtained from coal tar pitch, has fine particles of a mesophase pitch sphere having a caking substance in the surface layer and residual volatile matter, and further fused lumps are finely crushed, preferably the coke pulverization It was found that the amorphous carbonaceous particles obtained by subjecting a mixture of a graphite powder mainly composed of a substance to a surface treatment with an oxygen-containing organic substance and then heat-treating at 800 to 1300 ° C. are extremely effective in achieving the above-mentioned object, The present invention has been completed.

That is, the present invention is a carbonaceous particle (1) having a heat-treated carbonaceous substance of an oxygen-containing organic substance on the surface of a pulverized coke of mesophase pitch. In another invention, 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 (Lc) in the C-axis direction is 0.8 to 10 nm, and Specific gravity is 1.7-2.1
The carbonaceous particles (2) are in the range. Still another invention is a negative electrode for a lithium ion secondary battery containing the carbonaceous particles (1 or 2).

The present invention will be described in detail below. The green coke pulverized product of mesophase pitch used in the present invention is, for example, petroleum-based or coal-based tar pitch by naphtha decomposition, petroleum decomposition, thermal decomposition of coal, asphalt decomposition, etc. It is obtained by further fusing mesophase pitch small spheres generated when heated at ˜500 ° C., separating as a lump, and then pulverizing the mixture.
98% by weight, quinoline-soluble content 20 to 5% by weight, volatile content (weight ratio decreasing at 800 ° C. for 7 minutes) 6 to 25% by weight, and the average particle diameter is 1 to 15 μm.
m, preferably 3 to 10 μm.

The oxygen-containing organic material used in the present invention is not particularly limited as long as it has fixed carbon after heat treatment, and examples of such oxygen-containing organic material include:
Phenolic resin (novolak type, resol type, benzylic ether type), furan resin, furfuryl alcohol, melamine resin, urea resin, epoxy resin, polyimide resin, unsaturated polyester resin, polyurethane resin,
Examples thereof include starch, sucrose, cellulose, 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, phenol resin, furan resin, furfuryl alcohol, starch and sucrose are preferable because they have a high fixed carbon. Particularly preferred is a phenolic resin. These may be used alone or in combination of two or more. Although the amount of the oxygen-containing organic substance used is not particularly limited, it is generally 3% by weight or more in terms of solid content with respect to the pulverized mesophase coke or the mixture thereof with graphite.
However, considering workability during coating and heat treatment, 5
It is preferably ˜50% by weight. If necessary, other additives such as tar pitch and powder coke can be used in combination with such oxygen-containing organic matter.

In the carbonaceous particles according to the present invention, for example, the surface of a green coke pulverized product of the above mesophase pitch or a mixture of graphite powder mainly composed of the coke pulverized product is treated with an oxygen-containing organic substance to remove water or a solvent. After heat removal, heat treatment is performed in an inert gas atmosphere to fuse the oxygen-containing organic matter (especially phenol resin) with the caking and residual volatile components of the surface layer of the coke pulverized product.
It is manufactured as amorphous particles formed by repeating separation. In particular, in order to obtain carbonaceous particles suitable for a negative electrode for a lithium ion secondary battery, a heat treatment temperature is 800 to 1300 ° C.,
It is particularly desirable that the temperature is 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, and if the temperature exceeds 1300 ° C., the discharge electricity amount is almost the same as that of the heat-treated product of the pulverized green coke of mesophase pitch. Among such carbonaceous 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 (Lc) in the C-axis direction is 0.8 to 10 nm, It is preferable that the true specific gravity is in the range of 1.7 to 2.1, especially 1.8 to 2.1, and it is possible to realize a large electric capacity and reduce the overvoltage. The graphite powder is preferably used in the production of carbonaceous particles for a negative electrode, and is usually used as a mixture with a crushed product of coke as described above or as a mixture with an oxygen-containing organic material in advance. You may use it, mixing with the coke pulverized product surface-treated with the oxygen organic substance. The blending amount thereof is usually 0.1% by weight, preferably 5 to 10% by weight from the viewpoint of battery safety, with respect to the coke pulverized product. Further, in the production of the carbon particles of the present invention, since the surface of the coke pulverized product is treated with an oxygen-containing organic substance, a pretreatment for removing the caking substance in the surface layer of the coke pulverized product, such as a conventional low temperature treatment. Crosslinking treatment by heat treatment,
It is not necessary to perform complicated control of controlling the fusion property by performing oxidative crosslinking treatment with oxygen.

More specifically, such carbonaceous particles include the above-mentioned mesophase pitch green coke pulverized product (preferably a mixture with graphite powder mainly composed of the coke pulverized product), the oxygen-containing organic substance, and if necessary. After adding the additives such as the tar pitch, which are added as described above, to a kneading machine capable of stirring and mixing, such as a heating kneader, the one that is subjected to stirring and mixing treatment up to a temperature of 120 to 180 ° C. is transferred to a heat treatment furnace, An atmosphere that does not easily oxidize,
For example, in an atmosphere of nitrogen, argon, etc., from room temperature to 500
After heat treatment at a temperature rising rate appropriately selected from the range of 0.05 to 0.5 ° C / minute up to ℃, 0.05 to 10 ° C / minute until the temperature exceeds 500 ° C. It can be obtained by performing heat treatment at a heating rate appropriately selected from the range. In this case, it is preferable to use an aqueous solution or an organic solvent solution in advance for the oxygen-containing organic material that is difficult to be heated and melted.

The negative electrode for a lithium ion secondary battery according to the present invention comprises the above-mentioned carbonaceous particles and a binder such as carboxymethyl cellulose, fluororubber, polyvinylidene fluoride, polyvinyl pyridine, polyvinyl alcohol, polyacrylate, EPDM rubber, The dispersion liquid with a diene-based rubber or the like is applied onto a current collector such as a metal foil of copper, stainless steel, or nickel having a thickness of 1 to 50 μm, a mesh body, a porous body, etc., dried, and pressed. can get.

In the lithium ion secondary battery according to the present invention, the positive electrode is made of, for example, Li _x Co _y M _z O ₂ (where M is Al, In, Sn,
It represents at least one metal selected from Mn, Fe, Ti, Zr, and Ce, and x, y, and z are 0 <x ≦ 1.
1, 0.5 <y ≦ 1, z ≦ 0.15), Li
_x CoO 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
(However, M represents at least one kind of metal selected from Mn, Ti, and Fe, and x and z are 0 <x ≦ 1, respectively.
0.1 <z ≦ 0.3), and lithium manganese oxides such as 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 and 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
O ₂ ) ₂ NLi or any one of a mixture of two or more lithium salts, and the solvent is, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,
2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-
Dioxolane, 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, etc., or a mixture of two or more thereof, and the separator is a single fine film of a polyolefin microporous membrane such as polyethylene or polypropylene, or one or two thereof.
It refers to a bonded film of at least one kind and a film using a carbonaceous material as an active material as a negative electrode.

The negative electrode for a lithium ion secondary battery of the present invention may be used as it is as the above-mentioned positive electrode, electrolytic solution and separator, and may be doped with lithium ions from the positive electrode at the time of initial charging. , Lithium alloy, or lithium iodide may be contacted and doped.

[0016]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. (Measurement method) Current efficiency (%) is discharge electricity quantity / charge electricity quantity x 100
It is represented by. The discharge capacity (mAh / g) of the negative electrode active material is obtained as the discharge electricity quantity per weight of the active material. The capacity retention rate (%) is a percentage of the discharge capacity ratio in a predetermined cycle with respect to the first discharge capacity. The layer thickness Lc (nm) of the carbon mesh plane in the C-axis direction and the interplanar spacing d ₀₀₂ (nm) of the carbon mesh plane are calculated by the X-ray diffraction method according to the “Japan Society for the Promotion of Science”. It should be noted that the calculation is performed by excluding the peak of the added graphite. The true specific gravity is measured according to the method of JIS K2151. Preparation of Negative Electrode 0.8 parts by weight of carboxymethyl cellulose as a binder and 2.0 parts by weight of styrene-butadiene crosslinked rubber latex particles are used with respect to 100 parts by weight of the carbonaceous particles obtained in Examples and Comparative Examples. 100 parts by weight of the aqueous solution is added to form a dispersion, which is applied to one side of an electrolytic copper foil having a thickness of 18 μm, dried, and compressed and pressed. 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 1.0 mol of LiBF _{4 had} 25% propylene carbonate, 25% ethylene carbonate, and 50% γ-butyrolactone by volume. In a mixed solvent having a specific rate, charging is started at a current density of 1.0 mA / cm ² for 8 hours. Vs. Li / Li + potential 1
Doping (charging) to 0 mV. Discharge is to Li /
The Li + potential was set to 1.0 V to obtain the discharge capacity, which was expressed as mAh / g as the discharge electricity quantity per weight of the active material. For the overvoltage (V), the voltage drop at the moment of the start of discharge is determined at a constant current of 1.0 mA / cm ² .

(Example 1) 100 parts by weight of pulverized green coke of petroleum-based mesophase pitch (average particle size 10 μm, toluene insoluble content 94% by weight, quinoline soluble content 10% by weight, volatile content 8% by weight) and graphite After mixing 7 parts by weight of powder and 30 parts by weight of liquid resol type phenol resin (solid content) with a Henschel mixer, the temperature is raised from room temperature to 160 ° C. over 2 hours while stirring with a heating kneader to carry out condensation and crosslinking. , Dehydrate. 160 ℃ for another 30 minutes
Hold on. Next, this is transferred to an electric furnace and heated to 900 ° C. at a temperature rising rate of 0.2 ° C./min from room temperature to 500 ° C. and 2 ° C./min after 500 ° C. in a nitrogen atmosphere, and further 30 ° C.
By holding it for a minute, carbonaceous particles for producing a negative electrode for a lithium ion secondary battery were obtained. Table 1 shows the characteristics of the obtained carbonaceous particles and the evaluation results of the negative electrode prepared using the same.

Example 2 Pulverized green coke of coal-based mesophase pitch (average particle size 7 μm, toluene insoluble content 96% by weight, quinoline soluble content 9% by weight, volatile content 1)
100 parts by weight, 6 parts by weight of graphite powder and 30 parts by weight of a novolak type phenolic resin having curability are mixed in a Henschel mixer, and then the mixture is heated from room temperature to 160 ° C. while stirring with a heating kneader. Crosslinks by raising the temperature over time. Hold at 160 ° C. for an additional 30 minutes. Next, this was transferred to an electric furnace, and under a nitrogen atmosphere, from room temperature to 500 ° C, 0.2 ° C / min, and after 500 ° C, 2 ° C / min.
The temperature was raised to 1100 ° C. at a heating rate of 1 minute, and the temperature was maintained for 30 minutes to obtain carbonaceous particles for producing a negative electrode for a lithium ion secondary battery. Table 1 shows the characteristics of the obtained carbonaceous particles and the results of the negative electrode prepared using the same.

Example 3 100 parts by weight of petroleum-based mesophase pitch green coke pulverized product (average particle size 10 μm, toluene insoluble content 94% by weight, quinoline soluble content 10% by weight, volatile content 8% by weight) and graphite After mixing 4 parts by weight of powder, 15 parts by weight of liquid resol type phenol resin (solid content) and 30 parts by weight of coal pitch with a Henschel mixer, it takes 2 hours from room temperature to 160 ° C. while stirring with a heating kneader. Then, the temperature is raised to condense, crosslink, and remove the solvent. Hold at 160 ° C. for an additional 30 minutes. Next, this is transferred to an electric furnace and heated to 1200 ° C. at a temperature rising rate of 0.2 ° C./min from room temperature to 500 ° C. and 2 ° C./min after 500 ° C. in a nitrogen atmosphere, and further for 30 minutes. By holding, carbonaceous particles for producing a negative electrode for a lithium ion secondary battery were obtained. Table 1 shows the characteristics of the obtained carbonaceous particles and the evaluation results of the negative electrode prepared using the same.

(Comparative Example 1) The same petroleum-based mesophase pitch green coke pulverized product as in Example 1 was subjected to the same heat treatment as in Example 1 and sintered. Carbonaceous particles for producing a negative electrode for a secondary battery were obtained. Table 1 shows the characteristics of the obtained carbonaceous particles and the evaluation results of the negative electrode prepared using the same.

(Comparative Example 2) The same petroleum-based mesophase pitch green coke pulverized product as in Example 1 was extracted with quinoline and then subjected to the same heat treatment as in Example 1 to prepare a negative electrode for a lithium ion secondary battery. Carbonaceous particles were obtained.
Table 1 shows the characteristics of the obtained carbonaceous particles and the evaluation results of the negative electrode prepared using the same.

Comparative Example 3 Phenol resin alone in a nitrogen atmosphere in an electric furnace from room temperature to 500 ° C.
After heating at 2 ° C / min, 500 ° C or higher to 1200 ° C at 2 ° C / min, holding for 30 minutes, and then crushing this to obtain carbonaceous particles for producing a negative electrode for a lithium ion secondary battery. It was Table 1 shows the characteristics of the obtained carbonaceous particles and the evaluation results of the negative electrode prepared using the same.

(Comparative Example 4) The same composition as in Example 1 was used in an electric furnace in a nitrogen atmosphere at a temperature from room temperature to 500 ° C. of 0.2.
The carbonaceous particles for producing a negative electrode for a lithium ion secondary battery were obtained by performing heat treatment at a temperature rising rate of 2 ° C./min from 500 ° C./min to 500 to 750 ° C. Table 1 shows the characteristics of the obtained carbonaceous particles and the evaluation results of the negative electrode prepared using the same.

Comparative Example 5 The same composition as in Example 1 was heat-treated under the same temperature conditions as in Example 1, and further heat-treated at a temperature rising rate of 2 ° C./min up to 1350 ° C. to obtain a lithium ion secondary Carbonaceous particles for producing a battery negative electrode were obtained. Table 1 shows the characteristics of the obtained carbonaceous particles and the evaluation results of the negative electrode prepared using the same.

Comparative Example 6 Table 1 shows the characteristics of a conventional petroleum pitch coke (needle coke) and the evaluation results of a negative electrode for a lithium ion secondary battery prepared by using the same.

As shown in Table 1, these results are compared with the petroleum-based pitch coke, which is the prior art of Comparative Example 6 in initial discharge capacity in Examples 1 to 3 according to the present invention. Is extremely large at 118-185%,
The current efficiency at the 5th cycle, which is the capacity retention rate, is 10
It is 0%, and the overvoltage is equal to or less than that of the conventional example. However, if the heat treatment temperature is lower than 800 ° C., the initial current efficiency is significantly lowered, which is not preferable. On the other hand, when the temperature exceeds 1300 ° C., the amount of discharged electricity becomes almost the same as that of the heat-treated product of the green coke pulverized product of mesophase pitch alone.

[0027]

[Table 1]

[0028]

INDUSTRIAL APPLICABILITY According to the present invention, a green coke pulverized product of mesophase pitch, preferably a mixture of the pulverized coke and graphite powder, is surface-treated with an oxygen-containing organic compound such as a phenol resin, and is inert. 800 to 1300 ° C. in a gas atmosphere, preferably 900 to 12
The carbonaceous particles obtained by heat treatment at 00 ° C. have a relatively high true specific gravity, and when used as a negative electrode active material, the carbonaceous particles are 118 to 1 in comparison with the conventional petroleum pitch coke.
It is possible to provide a negative electrode for a lithium-ion secondary battery that exhibits a specific high discharge electricity amount of 85%, is excellent in safety, and has a small overvoltage.

Claims (3)

[Claims] 1. A carbonaceous particle characterized by comprising a heat-treated carbonaceous substance of an oxygen-containing organic substance on the surface of a crushed product of coke of mesophase pitch. 2. The average particle diameter is 60 μm or less, the carbon interlayer distance (d ₀₀₂ ) is 0.370 to 0.350 nm, and C
The negative electrode for a lithium ion secondary battery according to claim 1, wherein the axial crystallite thickness (Lc) is 0.8 to 10 nm and the true specific gravity is in the range of 1.7 to 2.1. Suitable carbonaceous particles. 3. A negative electrode for a lithium ion secondary battery, which comprises the carbonaceous particles according to claim 1 or 2.