JP3091949B2 - Method for producing silicon-containing carbon particles and negative electrode comprising the carbon particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing silicon-containing carbon particles and a negative electrode comprising 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 a lithium ion secondary battery containing the carbon particles.

[0002]

2. Description of the Related Art In recent years, a lithium ion secondary battery is a high energy storage battery which can be reduced in size and weight.
It is attracting attention as a power source for portable electronic devices. And
In the lithium ion secondary battery, the positive electrode active _{material, Li x M y O z (} M is one or more metal elements mainly containing a transition metal element, 0.5 ≦ x ≦ 2 , 1 ≦ y ≦
Lithium metal composite oxide particles represented by (2, 2 ≦ z ≦ 4) are used, and carbonaceous materials such as petroleum pitch coke, coal pitch coke, and graphite particles are used for the negative electrode.

The energy density indicating the battery performance depends on the degree of lithium ion doping (occluding) of a carbonaceous material as an active material of a negative electrode. The positive electrode active material emits 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 larger amount of the negative electrode active material is filled into the limited internal volume of the battery can, a large discharge electric capacity per negative electrode active material leads to a higher capacity of the battery. As a power source for various electronic and electric devices, there is a further demand for a battery that can be charged within two hours and has a higher capacity.

A carbide obtained by heat-treating petroleum pitch coke, coal pitch coke, or the like used as a negative electrode active material at 700 to 800 ° C. has a high discharge electric capacity per gram of carbide, but has a high chargeability. It was inferior and had a true specific gravity of 1.50 to 1.75 g / cm ³ , and it was difficult to obtain a material per volume exceeding graphite. On the other hand, natural graphite and artificial graphite as graphite used as a negative electrode active material can achieve high capacity by selecting an aprotic organic solvent as an electrolytic solution. Although the surface area per unit weight of these graphites increases as the particle size decreases, the capacity increases, but the electric capacity is limited to 372 mAh / g. In addition, during rapid charging, the graphite surface becomes more active and lithium is easily precipitated, which may cause a problem in battery safety such as dendrite short-circuit, and the selection of a solvent is restricted because the electrolyte is easily decomposed. Will be done.

When graphite is used as a 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 suddenly drops below 3.4 V, gradually drops, and the residual battery capacity decreases. There is a disadvantage that the characteristics of a lithium ion secondary battery using coke, which was easy to display, as a 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 with benzene and a method of thermally decomposing a siloxane polymer such as polymethylphenylsiloxane or polyphenylsesquisiloxane have been proposed. However, the CVD method is expensive and it is difficult to obtain a uniform composition. In addition, the siloxane polymer is volatilized due to polymer cutting before carbonization, and the yield is poor.

[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 which can be produced at industrially useful economical efficiency, and include the carbon particles. An object of the present invention is to provide a negative electrode for a lithium ion secondary battery having high electric capacity and excellent safety.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, heat-treated a specific organosilicon compound or / and its polymer, graphite and further tar pitch. Then, they have found that a method for producing silicon-containing carbon particles obtained by carbonization and a 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 (where n is 0 or an integer of 1 to 3, and R is an organic group). And / or a heat treatment of an organosilicon compound (A) selected from a polymer thereof and graphite (B) at 650 to 1000 ° C., and 2 to 25% by weight of silicon and 5 to 5% by weight of graphite in the obtained carbide. To 75% by weight, 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 (where n is 0 or an integer of 1 to 3, and R is an organic group) and an organosilicon compound (A) selected from monomers and / or polymers thereof, and graphite (B) and tar pitch (C), 650 to 1000 At 25 ° C., and in the obtained carbide, silicon is 2 to 25% by weight and graphite is 5 to 75% by weight. Negative electrode for a lithium ion secondary battery.

Hereinafter, the present invention will be described in detail. The organosilicon compound (A) used in the present invention has a general formula (HO) _n -Si- (OR) _4-n (where n is an integer of 0 or 1 to 3, and R is an organic group) ), A polymer obtained by partial hydrolysis of such a monomer, or a mixture thereof. Note that R is an organic group, and the type thereof is not particularly limited. For example, 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, an alkenyl group such as a vinyl group, an allyl group, and an isopropenyl group, a benzyl group, a furfuryl group, and an acyl group. Further, different types of the 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. Fine particles having a particle diameter of 3 μm or less. In some cases, such graphite may be used by dispersing it in water or an organic solvent.

Examples of the tar pitch (C) used in the present invention include petroleum tar pitch and coal tar pitch obtained 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 phenolic resin is not particularly limited as long as it has a property of being crosslinkable at normal temperature or heating in the presence or absence of a curing agent or a curing accelerator, that is, a curable property. For example, novolak type, resol type or benzene Rick ether type phenol resins and resins obtained by modifying these with furan resins, furfuryl alcohol, melamine resins, xylene resins, and the like.

Further, any one or a mixture of green mesophase pitch small spheres and green mesophase pitch ground particles may be added to the tar pitch used in the present invention. These are prepared by setting the tar pitch to 300 to 600 ° C.
The mesophase pitch small spheres generated when heated to a temperature of 100 ° C. are centrifuged, or those in which the small spheres are fused are separated into a lump and then pulverized.
It may be fired at 600 ° C. or lower in an inert gas atmosphere or in a vacuum.

The mixture of the organosilicon compound (A), the graphite (B) and the tar pitch (C) is solidified at 100 to 160 ° C. under stirring in the presence of an acid catalyst such as oxalic acid and formic acid. 0.01 to 600 ° C in an active gas atmosphere
The temperature is raised at a rate of 2 ° C./min, and then 0.01 to 0.2 ° C.
650-1000 ° C., preferably 700-900 ° C. in an inert gas atmosphere or in a vacuum at a rate of
More preferably, heat treatment is performed to 700 to 800 ° C. to obtain a carbide. You may 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 the carbide is 5 to 15 μm.
m is preferred. The graphite content of the carbide is 5 to 75% by weight, preferably 20 to 70% by weight. If the graphite content is less than 5% by weight, the lithium ion secondary battery using this carbide as a negative electrode active material is inferior in quick chargeability, and if it exceeds 75% by weight, improvement in electric capacity cannot be exhibited. The silicon content of 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 carbides are extremely hardened and the electric capacity is hardly further improved.

The negative electrode for a lithium ion secondary battery of the present invention comprises the above-mentioned carbon particles alone or, if necessary, a mixture of other coke, graphite, etc., into which, for example, carboxymethyl cellulose, fluoro rubber, polyvinylidene fluoride, polyvinyl Dispersion composed of a mixture of any of pyridine, polyvinyl alcohol, polyacrylate, EPDM rubber, diene rubber, or a mixture thereof as a binder, for example, a metal such as copper, stainless steel, nickel, etc. having a thickness of 1 to 50 μm. It is obtained by applying it on a current collector such as a foil, a net, or a porous body, drying it, and pressing if necessary.

In the non-aqueous 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, Mn, F
e, at least one metal selected from Ti, Zr, and Ce, where x, y, and z are each 0 <x ≦ 1.1, 0.
5 <y ≦ 1, representing a number of 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 the lithium nickel oxide,
For example, Li _x NiO ₂ (0 <x ≦ 1), Li _x Ni _{y MzO 2}
(However, M represents at least one metal selected from Mn, Ti, and Fe, and x and z are each 0 <x ≦ 1, 0.
1 <z ≦ 0.5), 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 Mn
_{2-x O 4 (0 <} x ≦ 0.5), Li x Mn 2-y M y O 4 ( where, M represents Ni, Co, Ti, at least one metal selected from among Fe , X, y are respectively 0.5 ≦ x ≦
2, 0.1 <y ≦ 0.5), and examples of the lithium iron oxide include 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 satisfying 0 <x ≦ 0.2). Further, 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
A mixture of any one or more of 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-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 a mixture of two or more of these, and the separator is a single membrane of a polyolefin microporous membrane such as polyethylene or polypropylene, or a laminated membrane of one or more 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-described positive electrode, electrolytic solution, separator or solid electrolyte membrane, and may be doped with lithium ions from the positive electrode during the first charge, or The ions may be contacted with lithium metal, lithium alloy, lithium alkoxide, alkyllithium, or lithium iodide for doping.

[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 carbide as the active material. Preparation of negative electrode for lithium ion secondary battery 0.8 parts by weight of carboxymethyl cellulose as a binder and 100 parts by weight of carbon particles obtained in Examples and Comparative Examples, and crosslinked rubber latex particles of styrene-butadiene 2.0 And 100 parts by weight of an aqueous liquid containing 1 part by weight of the aqueous liquid, to obtain a dispersion, which is applied to one surface of an electrolytic copper foil having a thickness of 18 μm, dried, and compression-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 a volume fraction of 1.0 mol of LiBF ₄ propylene carbonate 25%, ethylene carbonate 25%, and γ-butyrolactone 50% was used. In the mixed solvent at a rate of 1.0 mA / cm ² at a maximum current density, charging is started for 8 hours. Doping (charging) is performed up to a Li / Li + potential of 10 mV. Discharge is to Li
/ Li + potential up to 1.5 V to determine the discharge capacity, which is expressed in mAh / g as the amount of discharge electricity per weight of active material. Quick chargeability Charge is started at a constant current of a current density of 3.0 mA / cm ² , and the ratio of the discharge electric capacity between the case of charging for 2 hours and the case of charging for 8 hours is determined as a percentage, and 80% or more is good. Is determined. The silicon content was measured at 815 ° C. after weighing the carbide (Wg).
After being burned in the air and incinerated, it was converted to Na ₂ O ₂ +
After melting in Na ₂ CO ₃ , the mixture is extracted with hydrochloric acid, perchloric acid is added, and the mixture is heated until white smoke is obtained. After washing by filtration, the filtrate is heated to 1100 ° C., cooled and weighed (W ₁ g). After weighing, it is treated with hydrofluoric acid, incinerated with high heat, weighed (W ₂ g) after cooling. The content of SiO ₂ in the incinerated sample is determined from the formula: SiO ₂ % = (W ₁ −W ₂ ) / W × 100, and is further converted to the silicon (Si) content of carbide. Residual capacity display performance When the discharge voltage as the negative electrode is 0.5 to 1.5 V and the ratio (percentage) of the discharge power is 10% or more of the discharge power, it is determined that the residual battery capacity display performance is good. .

(Example 1) As an organosilicon compound (A), 34 parts by weight of a tetramethylsilicate oligomer having an average degree of polymerization of 4 and 70% of graphite (B) obtained by jet milling an artificial graphite (average particle size: 3 μm) were used. Parts by weight and a coal-based tar pitch (softening point 80
C.) and 30 parts by weight of a resole-type phenol resin aqueous solution (17 parts by weight as a solid content) in a heating kneader, and the temperature is gradually increased from room temperature to 150 ° C. over 2 hours with stirring. Dehydrates, solidifies. 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 rate of 5 ° C./min, and thereafter, heat treatment is performed to 600 ° C. at a rate of 0.2 ° C./min to carbonize. Further, the temperature is raised at a rate of 2.0 ° C./min, 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 pulverized.
Sift through the mesh. Table 1 shows the measurement results including the evaluation results of the negative electrode using a 200 mesh pass product.

Example 2 42 parts by weight of a tetramethylsilicate oligomer having an average degree of polymerization of 4 as the organosilicon compound (A) and 50 parts of graphite (B) obtained by pulverizing a natural graphite by a jet mill (average particle size: 2 μm) were used. Parts by weight and coal-based tar pitch (softening point 89
° C) and 33 parts by weight of a 10% by weight aqueous oxalic acid solution in a heating kneader.
The temperature is gradually raised to 50 ° C. over 4 hours, dehydrated and solidified.
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 rate of 2 ° C./min, and thereafter, heat treatment is performed to 750 ° C. at a rate of 0.2 ° C./min to carbonize. This carbide was pulverized to an average particle diameter of 6 μm, and the obtained powder was crushed at 750 ° C. in an electric furnace in vacuum.
After the heat treatment for an hour, the mixture is cooled and taken out of the electric furnace. 2
Table 1 shows the measurement results including the evaluation results of the negative electrode using the 00 mesh pass product.

EXAMPLE 3 67 parts by weight of dimethyldiphenylsilicate (dimethoxydiphenoxysilane) as an organosilicon compound (A) and 20 parts of graphite (B) obtained by milling a natural graphite by a jet mill (average particle diameter: 3 μm) were used. Parts by weight, 73 parts by weight of a coal-based tar pitch (softening point: 80 ° C.) as a tar pitch (C), and 33 parts by weight of a 10% by weight aqueous oxalic acid solution are placed in a heating kneader, and the mixture is stirred and stirred at room temperature. The temperature is gradually raised to 160 ° C. over 4 hours to dehydrate and solidify. This 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 rate of 5 ° C./min, and thereafter, heat treatment is performed to 750 ° C. at a rate of 0.2 ° C./min to carbonize. The carbide is cooled in a stream of nitrogen and removed from the electric furnace. This is ground and sieved through a 200 mesh sieve. Table 1 shows the measurement results, including the negative electrode evaluation results using a 200 mesh pass product.
Shown in

Example 4 As an organosilicon compound (A), furfuryl silicate oligomer having an average degree of polymerization of 4 was used.
5 parts by weight, 20 parts by weight of a natural graphite jet mill ground product as graphite (B) (same as in Example 3), and coal-based tar pitch as tar pitch (C) (same as in Example 2)
Are premixed with 73 parts by weight of a oxalic acid aqueous solution and 33 parts by weight of a 10% by weight aqueous oxalic acid solution using a Henschel mixer. This is placed in a heating kneader, and while stirring, the temperature is gradually raised from room temperature to 160 ° C. over 4 hours to dehydrate and solidify. Cool this,
After being taken out and crushed, it is transferred to an electric furnace. Then, in a nitrogen atmosphere, the temperature is increased from room temperature to 200 ° C. at a rate of 5 ° C./min, and thereafter, at a rate of 0.2 ° C./min up to 600 ° C., and 2 ° C./min after 600 ° C. Heat treatment at a heating rate up to 700 ° C. to carbonize. When it reaches 700 ° C., it is cooled in a nitrogen stream and taken out of the electric furnace. The carbide is ground and sieved through a 200 mesh screen. Table 1 shows the measurement results, including the negative electrode evaluation results using a 200 mesh pass product.
Shown in

(Example 5) As the organosilicon compound (A), 65 parts by weight of the same furfuryl silicate oligomer as in Example 4, 33 parts by weight of tetraphenylsilicate (tetraphenoxysilane), and graphite (B) were used. 3
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 kneader, and 700
Heat treated to ℃ and carbonized. When it reaches 700 ° C., it is cooled in a nitrogen stream and taken out of the electric furnace. The carbide is ground and sieved through a 200 mesh screen. 200
Table 1 shows the measurement results including the evaluation results of the negative electrode using the mesh pass product.

Comparative Example 1 The same premix as in Example 4 was placed in a heating 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 pulverized. This was sieved through a 200-mesh sieve, and the measurement results are shown in Table 1, including the results of negative electrode evaluation using a 200-mesh pass product.

Comparative Example 2 100 parts by weight of the same furfuryl silicate oligomer as in Example 4 and 3 parts of an aqueous oxalic acid solution
3 parts by weight (corresponding to 3.3 parts by weight of oxalic acid) were 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 and carbonized.
Take it out and grind it. Table 1 shows the evaluation results including the negative electrode evaluation results of the 200 mesh pass product.

Comparative Example 4 Natural graphite having an average particle diameter of 6 μm was evaluated for a negative electrode, and the measurement results including the results are shown in Table 1.

Comparative Example 5 The same graphite as in Example 2
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 as in Example 4. The carbide is cooled in a nitrogen atmosphere, taken out of the electric furnace and pulverized. This was sieved through a 200-mesh sieve, and the measurement results are shown in Table 1, including the results of negative electrode evaluation using a 200-mesh pass product.

[0027]

[Table 1]

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

[0029]

According to the present invention, as shown in Examples 1 to 5, an extremely high discharge capacity with a true specific gravity of 1.8 or more and natural graphite or more is exhibited, as well as rapid chargeability and residual capacity display. Silicon-containing carbon particles excellent in stability can be obtained, and it is possible to provide a negative electrode for a lithium ion secondary battery having high electric capacity including the carbon particles and excellent in safety.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-231273 (JP, A) JP-A-8-40716 (JP, A) JP-A-5-270938 (JP, A) JP-A-7- 315822 (JP, A) JP-A-6-96759 (JP, A) JP-A-6-279112 (JP, A) JP-A-5-144474 (JP, A) JP-A-7-307165 (JP, A) JP-A-8-213012 (JP, A) JP-A-8-111243 (JP, A) Table 9-502566 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02 C04B 35/52 H01M 4/58

Claims (4)

(57) [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. And / or a heat treatment of an organosilicon compound (A) selected from a polymer thereof and graphite (B) at 650 to 1000 ° C., and 2 to 25% by weight of silicon and 5 to 5% by weight of graphite in the obtained carbide. To 75% by weight. 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. And / or heat treatment of an organosilicon compound (A) selected from a polymer thereof, graphite (B), and tar pitch (C) at 650 to 1000 ° C., and silicon in the obtained carbide is 2 to 25. A method for producing silicon-containing carbon particles, wherein the content of graphite is 5 to 75% by weight. 3. A negative electrode for a lithium ion secondary battery, comprising the carbon particles according to claim 1. 4. A negative electrode for a lithium ion secondary battery, comprising the carbon particles according to claim 2.