JPH08236104A - Manufacture of silicon-containing carbon particle and negative electrode containing the carbon particle - Google Patents

Abstract

PURPOSE: To economically manufacture silicon-containing carbon particles with high electric capacity by heat-treating a mixture of a specific organic silicon compound and graphite at a specified temperature to form a carbide containing a specified amount of silicon and graphite. CONSTITUTION: A mixture of an organic silicon compound comprising a monomer represented by a general formula: (HO)n -Si-(OR)4-n (wherein n is an integer of 0-3, and R is an organic group.) and/or its polymer, and graphite, and tar pitch if necessary is heat-treated at 650-1000 deg.C. The carbide obtained contains 2-25wt.% silicon and 5-75wt.% graphite. A negative electrode for a lithium ion secondary battery with high capacity and high safety can be provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing silicon-containing carbon particles and a negative electrode containing the carbon particles. More specifically, the present invention relates to a method for producing silicon-containing carbon particles having a high electric capacity and a negative electrode for lithium ion secondary batteries containing the carbon particles.

[0002]

2. Description of the Related Art In recent years, lithium-ion secondary batteries are high-energy storage batteries that can be made compact and lightweight.
It has attracted attention as a power source for portable electronic devices. And
In this lithium ion secondary battery, the positive electrode active material is Li _x M _y O _z (M is one or more metal elements mainly containing a transition metal element, and 0.5 ≦ x ≦ 2. , 1 ≦ y ≦
2, 2 ≦ z ≦ 4) lithium metal composite oxide particles are used, and a carbonaceous material such as petroleum pitch coke, coal pitch coke, and graphite particles is used for the negative electrode.

The energy density showing the battery performance depends on the degree of doping (storage) of lithium ions in the carbonaceous material which is the active material of the negative electrode. The positive electrode active material releases lithium ions during charging, is doped (charged) into the carbonaceous material of the negative electrode, and is dedoped (discharged) from the carbonaceous material during discharge. Since a large amount of the negative electrode active material is filled in the limited inner volume of the battery can, a large discharge electric capacity per negative electrode active material leads to a high capacity of the battery. Further, as a power source for various electronic / electrical devices, the advent of a battery that can be charged within 2 hours and has a higher capacity is further desired.

In the carbide obtained by heat-treating petroleum pitch coke, coal pitch coke, etc. used as the negative electrode active material at 700 to 800 ° C., although the discharge electric capacity per 1 g of the carbide is high, it has a high chargeability. It was inferior, and the true specific gravity was 1.50 to 1.75 g / cm ³ , and it was difficult to obtain one having a capacity per volume exceeding that of graphite. On the other hand, natural graphite and artificial graphite as the graphite used as the negative electrode active material can have a higher capacity by selecting an aprotic organic solvent as the electrolytic solution. Although the surface area per unit weight of these graphites increases as the particle diameter decreases, the capacity increases, but the electric capacity is limited to 372 mAh / g. Also, during rapid charging, the graphite surface is more activated and lithium is more likely to deposit, which may cause a problem in battery safety such as dendrite short-circuiting, and it is easy to decompose the electrolytic solution, which limits the choice of solvent. Will be done.

When graphite is used as the negative electrode active material, for example, in the case of a lithium ion secondary battery using lithium cobalt oxide for the positive electrode, the discharge voltage becomes abrupt at 3.4 V or less, and the voltage gradually decreases, resulting in a residual battery capacity. There is a drawback in that the features of the lithium-ion secondary battery using the coke, which was easy to display, as the negative electrode are lost. As carbon particles having higher electric capacity, by chemical vapor deposition (CVD),
A method of thermally decomposing SiCl ₄ or (CH ₃ ) ₂ Cl ₂ Si together with benzene and a method of thermally decomposing siloxane polymers such as polymethylphenylsiloxane and polyphenylsesquisiloxane have been proposed. However, the CVD method is expensive and it is difficult to obtain a composition having a uniform composition. In addition, the yield of siloxane polymers is poor because they are volatilized by cutting the polymer before carbonization.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned problems and to provide a method for producing carbon particles having a high electric capacity that can be produced with industrially useful economical efficiency and the carbon particles. Another object of the present invention is to provide a negative electrode for a lithium ion secondary battery, which has a high electric capacity and is excellent in safety.

[0007]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the inventors of the present invention heat treated a specific organosilicon compound or / and its polymer, graphite and tar pitch. Then, they have found that the method for producing silicon-containing carbon particles obtained by carbonization and the negative electrode containing the carbon particles are extremely effective in solving the above problems, and have completed the present invention. That is, the present invention provides a monomer represented by the general formula (HO) _n -Si- (OR) _4-n (wherein n is 0 or an integer of 1 to 3 and R is an organic group). Or, and / or heat treatment of an organosilicon compound (A) selected from the polymer and graphite (B) at 650 to 1000 ° C., and in the obtained carbide, 2 to 25% by weight of silicon and 5% by weight of graphite are contained. To 75% by weight, a method for producing silicon-containing carbon particles, or a negative electrode for a lithium ion secondary battery containing the silicon-containing carbon particles, or a general formula (HO) _n -Si- (OR). _4-n (wherein n is 0 or an integer of 1 to 3 and R is an organic group), an organosilicon compound (A) selected from a monomer and / or a polymer thereof, and graphite 650 to 1000 consisting of (B) and tar pitch (C) In a carbide obtained by heat treatment at ℃, 2 to 25% by weight of silicon, 5 to 75% by weight of graphite, a method for producing silicon-containing carbon particles, or containing the silicon-containing carbon particles Is a negative electrode for a lithium ion secondary battery.

The present invention will be described in detail below. The organosilicon compound (A) used in the present invention has the general formula (HO) _n —Si— (OR) _4-n (wherein n is 0 or an integer of 1 to 3 and R is an organic group). )), A polymer obtained by partial hydrolysis of such a monomer, or a mixture thereof. R is an organic group, and the type thereof is not particularly limited, but examples thereof include an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group, a phenyl group, a phenoxyphenyl group, a methylphenyl group, Examples thereof include an aryl group such as a biphenyl group, a vinyl group, an allyl group, an alkenyl group such as an isopropenyl group, a benzyl group, a furfuryl group, an acyl group and the like. Further, different types of the above-mentioned monomers or polymers may be used in combination.

The graphite (B) used in the present invention is natural graphite, artificial graphite or a mixture thereof, and is generally used in the form of powder or granules having an average particle diameter of 30 μm or less, but particularly preferably the average. The fine particles have a particle diameter of 3 μm or less. In some cases, such graphite may be dispersed in water or an organic solvent before use.

Examples of the tar pitch (C) used in the present invention include petroleum tar pitch, coal tar tar pitch and the like by naphtha cracking, crude oil cracking, coal thermal cracking, asphalt cracking and the like. If necessary, phenol resins may be added to the tar pitch. The phenol resin is not particularly limited as long as it has a property of being crosslinkable at room temperature or under heating in the presence or absence of a curing agent or a curing accelerator, that is, curability, and examples thereof include novolac type, resol type or benzine type. Examples thereof include rickether type phenolic resins and resins obtained by modifying these with furan resins, furfuryl alcohol, melamine resins, xylene resins and the like.

Further, to the tar pitch used in the present invention, any one or a mixture of the green mesophase pitch small spheres and the green mesophase pitch crushed particles may be added. These are the tar pitches of 300 to 600 ° C.
The mesophase pitch small spheres that are generated when heated to the above are separated by centrifugation, or the ones in which the smaller spheres are fused are separated into lumps and then crushed.
It may be baked at 600 ° C. or lower in an inert gas atmosphere or in a vacuum.

A mixture of the organosilicon compound (A), the graphite (B), and further the tar pitch (C) is solidified at 100 to 160 ° C. under stirring with an acid catalyst such as oxalic acid or formic acid, and 0.01 to 600 ° C in an active gas atmosphere
The temperature is raised at a heating rate of 2 ° C./min, and further 0.01 to 0.2 ° C.
650 to 1000 ° C., preferably 700 to 900 ° C. in an inert gas atmosphere or in a vacuum at a temperature rising rate of 1 / min.
More preferably, heat treatment is performed at 700 to 800 ° C. to obtain a carbide. You can crush this and use it as it is,
If necessary, vacuum heat treatment may be performed again at 700 to 900 ° C. The average particle size of this carbide is 5 to 15 μm.
m is preferable. The graphite content in this carbide is 5 to 75% by weight, preferably 20 to 70% by weight. If the graphite content is less than 5% by weight, the rapid chargeability of a lithium ion secondary battery using this carbide as a negative electrode active material is poor, and if it exceeds 75% by weight, improvement in electric capacity cannot be realized. The silicon content in the carbide is 2 to 25% by weight, preferably 4 to 15% by weight. If the silicon content is less than 2% by weight, the effect of improving the electric capacity by addition is small, and if it exceeds 25% by weight, the carbide becomes extremely hard and the electric capacity is hardly further improved.

The negative electrode for a lithium ion secondary battery of the present invention comprises the carbon particles alone or, if necessary, mixed with other coke, graphite or the like, and mixed with, for example, carboxymethyl cellulose, fluororubber, polyvinylidene fluoride or polyvinyl. A dispersion liquid composed of any one or a mixture of pyridine, polyvinyl alcohol, polyacrylate, EPDM rubber, diene rubber and the like as a binder, for example, a metal having a thickness of 1 to 50 μm, such as copper, stainless steel or nickel. It can be obtained by coating on a current collector such as a foil, a net-like body or a porous body, drying, and pressing if necessary.

In the non-aqueous secondary battery according to the present invention,
If the positive electrode is a lithium cobalt oxide, for example, Li
_x Co _y M _z O ₂ (where M is Al, In, Sn, Mn, F
e, Ti, Zr, Ce at least one kind of metal is selected, and x, y, and z are 0 <x ≦ 1.1, 0.
5 <y ≦ 1, z ≦ 0.15), Li _x CoO ₂
(0 <x ≦ 1.1), Li _x Co _y Ni _z O ₂ (0 <x ≦
1, y + z = 1), and 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 metal selected from Mn, Ti, and Fe, and x and z are 0 <x ≦ 1, 0.
1 <z ≦ 0.5), and lithium manganese oxides include, for example, LiMnO ₃ , Li _x MnO ₂ (0 <x
≦ 1), Li _x Mn ₂ O ₄ (0 <x <2), LiCo _x Mn
_2-x O ₄ (0 <x ≦ 0.5), Li _x Mn _{2- y My} O ₄ (where M represents at least one metal selected from Ni, Co, Ti and Fe) , X, y are each 0.5 ≦ x ≦
2, 0.1 <y ≦ 0.5), and as the lithium iron oxide, for example, LiFeO ₂ , LiFe _x M _1-x O
₂ (where M represents at least one metal selected from Mn, Ti, Co and Ni, and x represents a number of 0 <x ≦ 0.2). In addition, the electrolyte is, for example, L
iClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , CH
₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi
Any one or a mixture of two or more lithium salts, such as 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., any one kind or a mixture of two or more kinds thereof, the separator is one kind of a microporous polyolefin membrane such as polyethylene or polypropylene, a single kind of film, or one or more kinds of laminated films thereof, or a solid electrolyte. The film and the negative electrode are those using a carbonaceous material as an active material.

The negative electrode for a lithium ion secondary battery of the present invention may be used as it is with the above-mentioned positive electrode, electrolytic solution, separator or solid electrolyte membrane to dope lithium ions from the positive electrode at the time of initial charging, or to prepare lithium in advance. Ions may be brought into contact with lithium metal, a lithium alloy, lithium alkoxide, alkyllithium, or lithium iodide for doping.

[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 amount of discharged electricity per weight of the carbide that is the active material. Preparation of Negative Electrode for Lithium Ion Secondary Battery 0.8 part by weight of carboxymethyl cellulose as a binder and 2.0 parts by weight of styrene-butadiene crosslinked rubber latex particles with respect to 100 parts by weight of the carbon particles obtained in Examples and Comparative Examples. And 100 parts by weight of an aqueous liquid containing 1 part by weight to prepare a dispersion liquid, which is applied to one surface 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 contained 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 at maximum and charging is performed for 8 hours. Doping (charging) to a Li / Li + potential of 10 mV. Discharge against Li
/ Li + potential is measured up to 1.5 V to obtain the discharge capacity, which is expressed as mAh / g as the discharge electricity quantity per weight of the active material. Rapid chargeability: Start charging at a constant current with a current density of 3.0 mA / cm ² , start the charge for 2 hours and charge for 8 hours, find the ratio of the discharge electric capacity as a percentage, and 80% or more is good. To determine. The silicon content is 815 ° C. after weighing the carbide (Wg).
After burning in the air and incineration, this is Na ₂ O ₂ +
After melting the Na ₂ CO _3, and extracted with hydrochloric acid, heated to raise the white smoke by adding perchloric acid. After filtering and washing this, the filtered product is heated to 1100 ° C., cooled, and then weighed (W ₁ g). After weighing, hydrofluoric acid treatment is carried out to form ignited ash, and after cooling, weighing (W ₂ g) is performed. The content of SiO ₂ in the ashed sample is obtained from the formula of SiO ₂ % = (W ₁ -W ₂ ) / W × 100, and further converted into the silicon (Si) content of carbide. Remaining capacity displayability When the discharge voltage as the negative electrode has a ratio (percentage) of the discharged electricity amount of 0.5 to 1.5 V of 10% or more of the discharged electricity amount, it is judged that the residual battery capacity displayability is good. .

Example 1 34 parts by weight of tetramethyl silicate oligomer having an average degree of polymerization of 4 as the organosilicon compound (A) and 70 parts of a jet mill pulverized product (average particle size 3 μm) of artificial graphite as the graphite (B). Parts by weight and tar pitch (C) as coal-based tar pitch (softening point 80
30 parts by weight) and 17 parts by weight of a resol type phenolic resin aqueous solution (10 parts by weight as a solid content) are put into a heating type kneader and gradually raised from room temperature to 150 ° C. over 2 hours under stirring to carry out polymerization. , Dehydration and solidification. It is cooled, taken out and transferred to an electric furnace. Then, in a nitrogen atmosphere, the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 5 ° C./minute, and thereafter heat treated to carbonize at 600 ° C. at a temperature rising rate of 0.2 ° C./minute. Further, the temperature is raised at a heating rate of 2.0 ° C./minute, and when the temperature reaches 700 ° C., it is allowed to cool in a nitrogen stream.
Then, the carbide is taken out of the electric furnace and crushed to obtain 200
Sift through a mesh. The measurement results are shown in Table 1 including the negative electrode evaluation results for the 200 mesh pass product.

Example 2 42 parts by weight of tetramethyl silicate oligomer having an average degree of polymerization of 4 as the organosilicon compound (A), and 50 parts of a natural graphite jet-milled product (average particle diameter 2 μm) as the graphite (B) were used. Parts by weight and tar pitch (C) as coal-based tar pitch (softening point 89
C.) and 73 parts by weight of a 10% by weight aqueous solution of oxalic acid are put in a heating kneader and stirred at room temperature for 1 hour.
The temperature is gradually raised to 50 ° C. over 4 hours to dehydrate and solidify.
It is cooled, taken out and transferred to an electric furnace. Then, in a nitrogen atmosphere, the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 2 ° C./minute, and thereafter heat-treated to 750 ° C. at a temperature rising rate of 0.2 ° C./minute to carbonize. This carbide was crushed to have an average particle size of 6 μm, and the obtained powder was crushed in vacuum in an electric furnace at 750 ° C. for 1 hour.
After heat treatment for an hour, it is cooled and taken out of the electric furnace. Two
The measurement results are shown in Table 1 including the negative electrode evaluation results for the 00 mesh pass product.

Example 3 67 parts by weight of dimethyldiphenylsilicate (dimethoxydiphenoxysilane) as the organosilicon compound (A) and 20 parts of a natural graphite jet-milled product (average particle diameter 3 μm) as the graphite (B) were used. Part by weight, 73 parts by weight of coal-based tar pitch (softening point 80 ° C.) as tar pitch (C), and 33 parts by weight of 10% by weight oxalic acid aqueous solution were put in a heating kneader, and the mixture was stirred at room temperature to room temperature. The temperature is gradually raised to 160 ° C. over 4 hours to dehydrate and solidify. It is cooled, taken out, crushed and transferred to an electric furnace. Then, in a nitrogen atmosphere, the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 5 ° C./minute, and thereafter heat-treated to 750 ° C. at a temperature rising rate of 0.2 ° C./minute to carbonize. This carbide is cooled in a nitrogen stream and taken out of the electric furnace. This is ground and sifted through a 200 mesh screen. The measurement results are shown in Table 1 including the negative electrode evaluation results for the 200 mesh pass product.
Shown in

Example 4 6 furfuryl silicate oligomer having an average degree of polymerization of 4 was used as the organosilicon compound (A).
5 parts by weight, 20 parts by weight of a jet-milled product of natural graphite as graphite (B) (same as in Example 3), and coal-based tar pitch as tar pitch (C) (same as in Example 2)
And 73 parts by weight of a 10% by weight aqueous oxalic acid solution are premixed with a Henschel mixer. This is put in a heating type kneader, and the temperature is gradually raised from room temperature to 160 ° C. over 4 hours under stirring to dehydrate and solidify. Cool it down,
After taking out and crushing, it is transferred to an electric furnace. Then, in a nitrogen atmosphere, the temperature is increased from room temperature to 200 ° C. at a temperature increase rate of 5 ° C./min, thereafter up to 600 ° C. at a temperature increase rate of 0.2 ° C./min, and after 600 ° C. an increase of 2 ° C./min. It is heat-treated at a temperature rate up to 700 ° C. and carbonized. When it reached 700 ° C., it was cooled in a nitrogen stream and taken out of the electric furnace. The carbide is ground and sieved through a 200 mesh screen. The measurement results are shown in Table 1 including the negative electrode evaluation results for the 200 mesh pass product.
Shown in

Example 5 65 parts by weight of the same furfuryl silicate oligomer as in Example 4 as the organosilicon compound (A), 33 parts by weight of tetraphenyl silicate (tetraphenoxysilane), and graphite (B) were used as examples. Three
40 parts by weight of the same graphite and 33 parts by weight of a 10% by weight aqueous oxalic acid solution are premixed with a Henschel mixer.
This was put in a heating type kneader and 700
Heat it to ℃ and carbonize it. When it reached 700 ° C., it was cooled in a nitrogen stream and taken out of the electric furnace. The carbide is ground and sieved through a 200 mesh screen. 200
The measurement results are shown in Table 1 including the negative electrode evaluation results of the mesh pass product.

(Comparative Example 1) The same premix as in Example 4 was put in a heating type kneader and heated in the same manner as in Example 4,
The temperature is raised to 1400 ° C. and carbonized. The carbide is cooled in a nitrogen atmosphere, removed from the electric furnace and ground. This is passed through a 200-mesh screen, and the measurement results are shown in Table 1 including the negative-electrode evaluation results for the 200-mesh passed product.

Comparative Example 2 100 parts by weight of the same furfuryl silicate oligomer as in Example 4 and 3 parts of an oxalic acid aqueous solution were added.
3 parts by weight (corresponding to 3.3 parts by weight of oxalic acid) are carbonized at 750 ° C. in the same manner as in Example 3 and evaluated. Table 1 shows the results.

(Comparative Example 3) The same tar pitch as in Example 2 was heat treated in an electric furnace in the same manner as in Example 3 to be carbonized,
This is taken out and crushed. Table 1 shows the evaluation results including the negative electrode evaluation results for the 200 mesh pass product.

Comparative Example 4 A negative electrode of natural graphite having an average particle size of 6 μm was evaluated, and the measurement results including the results are shown in Table 1.

(Comparative Example 5) The same graphite as in Example 2 was used.
Parts by weight and 164 parts by weight of the same tar pitch as in Example 2 are put into a heating kneader, and heat treated and carbonized in the same manner as in Example 4. The carbide is cooled in a nitrogen atmosphere, taken out of the electric furnace and ground. This is passed through a 200-mesh screen, and the measurement results are shown in Table 1 including the negative-electrode evaluation results for the 200-mesh passed product.

[0027]

[Table 1]

Comparative Examples 1, 2 and 5 are inferior in discharge capacity. Further, in Comparative Examples 2 and 3, the true specific gravity is low. Comparative Example 4 (graphite) is inferior in rapid chargeability and remaining capacity displayability.

[0029]

EFFECTS OF THE INVENTION According to the present invention, as shown in Examples 1 to 5, the true specific gravity is 1.8 or more, and the extremely high discharge capacity higher than that of natural graphite is exhibited, and the quick chargeability and the residual capacity are displayed. It is possible to provide a silicon-containing carbon particle having excellent properties, and to provide a negative electrode for a lithium ion secondary battery which contains the carbon particle and has a high electric capacity and is excellent in safety.

Claims (4)

[Claims] 1. A monomer represented by the general formula (HO) _n --Si-(OR) _4-n (wherein n is 0 or an integer of 1 to 3 and R is an organic group). Or, and / or heat treatment of an organosilicon compound (A) selected from the polymer and graphite (B) at 650 to 1000 ° C., and in the obtained carbide, 2 to 25% by weight of silicon and 5% by weight of graphite are contained. ~ 75% by weight, a method for producing silicon-containing carbon particles. 2. A monomer represented by the general formula (HO) _n --Si-(OR) _4-n (wherein n is 0 or an integer of 1 to 3 and R is an organic group). Or / and heat treatment of an organosilicon compound (A) selected from its polymer, graphite (B) and tar pitch (C) at 650 to 1000 ° C., and the obtained carbide contains 2 to 25 silicon. %, And 5 to 75% by weight of graphite, the method for producing silicon-containing carbon particles. 3. A negative electrode for a lithium ion secondary battery, which comprises the carbon particles according to claim 1. 4. A negative electrode for a lithium ion secondary battery, which comprises the carbon particles according to claim 2.