JP3289231B2 - Negative electrode for lithium ion secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium ion secondary battery negative electrode comprising particles of coal <br/> product that have a high electrical capacity.

[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 solvent selection 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.

[0006]

An object of the present invention is to provide a, to overcome the above problems, an excellent safety have capacitance have high coal
It is an object of the present invention to provide a negative electrode for a lithium ion secondary battery , comprising particles of a compound .

[0007]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, added a specific metal or a compound containing the metal element to form a specific carbonaceous material and tar pitch. For lithium ion secondary batteries containing carbide particles obtained by heat-treating and carbonizing
The inventors have found that the negative electrode is extremely effective in solving the above-mentioned problems, and have completed the present invention. That is, in the present invention, the average particle diameter is 1 to 20 μm, and the carbon interlayer distance (d ₀₀₂ ) is 0.3.
A carbonaceous material (A) and a tar pitch (B) in the range of 35 to 0.340 nm, and one metal selected from aluminum, zinc, tin and silicon, or a compound containing any one of these metal elements Is mixed with one or more kinds of mixtures (C), and the mixture is heat-treated to obtain a carbide. In the carbide, (A) is 10 to 60% by weight, and carbonaceous material derived from (B) is 80% by weight. -20% by weight, metal element derived from (C) is 2-20%
It is characterized by comprising particles of weight% der Ru carbides
A negative electrode for a lithium ion secondary battery that.

Hereinafter, the present invention will be described in detail. Since the carbonaceous material (A) used in the present invention is required to have a rapid chargeability within 2 hours, the average particle diameter is 1 to 20.
μm, preferably 1 to 5 μm, and the carbon interlayer distance (d
₀₀₂ ) is from 0.335 to 0.340 nm, and is formed, for example, by subjecting natural graphite or artificial graphite to impact pulverization or intercalating the stage 1 with concentrated sulfuric acid or the like, followed by washing with water. Alternatively, a polymer material heat-treated at 2100 ° C. or higher, or a carbide such as pitch tar may be used.

Examples of the tar pitch (B) used in the present invention include petroleum tar pitch and coal tar pitch 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.

[0010] 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 component (C) used in the present invention is one kind of metal selected from aluminum, zinc, tin and silicon or one or two kinds of compounds containing any one of these metal elements.
A mixture of more than one kind (hereinafter, referred to as a specific metal compound, etc.), for example, tin and its compounds include tin metal powder, oxides, carboxylates such as tin acetate, halogen compounds such as stannous chloride, There are inorganic acid salts such as tin phosphate and organic tin compounds such as dibutyltin oxide. Silicon and its compounds include silicon metal powder, silicon dioxide, silicon tetrachloride, silicic acid, polysiloxane, and silazane. Aluminum and its compounds include aluminum metal powders, aluminum-based coupling agents such as aluminum hydroxide and acetoalkoxyaluminum diisopropylate, aluminum chelate particles such as aluminum ethyl acetoacetate isopropylate, aluminum isopropoxide, etc. Alcoholates. Examples of zinc and its compounds include zinc metal powder, carboxylate salts such as zinc hydroxide, zinc oxide, diethyl zinc, and zinc acetate; halides such as zinc chloride; and inorganic acids such as zinc carbonate, zinc nitrate, and zinc phosphate. Salts and carbamates such as zinc diethyldithiocarbamate.

The carbonaceous material (A), the tar pitch (B) and the specific metal compound (C) are mixed in an inert gas atmosphere by a mixer such as a Henschel mixer.
Then, it is heated to 400 ° C. in an inert gas atmosphere, solidified, and cooled to room temperature. If necessary, this is pulverized, and then again in an inert gas atmosphere or vacuum at a rate of 650-1000 ° C./min at a rate of 0.01-0.2 ° C./min.
° C, preferably 700 to 900 ° C, more preferably 7 ° C.
Heat treatment to 00 to 800 ° C to obtain carbide. On this occasion,
Hydrogen gas may be introduced into the atmosphere as needed.
The carbide particles preferably have an average particle diameter of 5 to 15 μm. In this carbide, the carbonaceous material (A) is 10 to 60% by weight, the carbonaceous material derived from the tar pitch (B) is 80 to 20% by weight, and the metal element derived from the specific metal compound (C) such as a specific metal compound is an atom. 2 to 20% by weight. If the amount of the metal element derived from the specific metal compound (C) is less than 2% by weight, the effect of improving the electric capacity by adding the metal element is small, and if it exceeds 20% by weight, the reduced metal atoms are present on the surface of the carbide particles. It is not preferable because it easily comes out and an alloy with lithium is easily formed on the surface, and the high-temperature stability of the battery deteriorates. If the carbonaceous material (A) is less than 10% by weight or more than 60% by weight, the quick chargeability is poor. Further, it is difficult to achieve the high electric capacity which is the object of the present invention.

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, fluorine 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 such that 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,
Proponitrile, 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. The plane spacing d ₀₀₂ (nm) of the carbon net plane is calculated by an X-ray diffraction method according to the “Japan Society for the Promotion of Science”. 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%, 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 metal element content was measured by X-ray fluorescence analysis for tin and zinc, and by atomic absorption method for aluminum and silicon. 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 a carbonaceous material (A), a product obtained by pulverizing artificial graphite with a jet mill (average particle diameter 3 μm, carbon interlayer distance (d ₀₀₂ ) 0.33)
6 nm), 97 parts by weight of coal tar pitch (softening point: 84 ° C.) as tar pitch (B), and 91 parts by weight of aluminum isopropylate as specific metal compound (C) in an autoclave. The temperature is gradually increased from room temperature to 300 ° C. over 3 hours under a high-speed stirring in a nitrogen atmosphere. This is once cooled, returned to room temperature under stirring, taken out, and transferred to an electric furnace. And in a nitrogen atmosphere,
The temperature is raised from room temperature to 750 ° C. at a rate of 0.2 ° C./min to carbonize. Then, the carbide was taken out of the electric furnace, passed through a 200-mesh sieve, and evaluated for a negative electrode using a 200-mesh pass product. The results are summarized in Table 1.

(Example 2) A pulverized product of natural graphite as the carbonaceous material (A) (average particle size 2.8 µm, carbon interlayer distance (d ₀₀₂ ) 0.335 nm)
30 parts by weight, 100 parts by weight of coal-based tar pitch (softening point 89 ° C.) as the tar pitch (B), and 13 parts by weight of a novolak-type phenol resin (including 1.3 parts by weight of hexamethylenetetramine as a curing agent) And 22 parts by weight of anhydrous zinc acetate as the specific metal compound (C),
In the same autoclave as in Example 1, the temperature is gradually increased from room temperature to 350 ° C. over 4 hours under high-speed stirring in a nitrogen atmosphere. After reaching 350 ° C., the mixture is cooled to room temperature with stirring.
Take it out and transfer to electric furnace. Then, in a nitrogen atmosphere, the temperature is raised from room temperature to 750 ° C. at a rate of 0.2 ° C./min to carbonize. This carbide was sieved through a 200-mesh sieve, and a 200-mesh pass product was evaluated as a negative electrode. The results are summarized in Table 1.

(Example 3) 30 parts by weight of the same carbonaceous material (A) as in Example 1; 95 parts by weight of the same tar pitch as in Example 1 as tar pitch (B); Example 1 Resin (solid content): 14 parts by weight and 21 parts by weight of dibutyltin oxide as the specific metal compound (C)
While gradually stirring in a nitrogen stream in the same autoclave as above, the temperature is gradually raised from room temperature to 250 ° C. over 5 hours. When it reaches 250 ° C., it is then cooled to room temperature with stirring. This is taken out, transferred to an electric furnace, and carbonized in a nitrogen atmosphere from normal temperature to 750 ° C. at a rate of 0.2 ° C./min. This carbide was sieved through a 200-mesh sieve, and a 200-mesh pass product was evaluated as a negative electrode.
The results are summarized in Table 1.

Example 4 30 parts by weight of the same carbonaceous material (A) as in Example 1; 90 parts by weight of the same tar pitch as in Example 1 as tar pitch (B); and resol phenol 10 parts by weight of the resin (solid content) and 51 parts by weight of orthosilicic acid as the specific metal compound (C) are placed in a heating kneader and heated from room temperature to 170 ° C. Then, it is cooled, transferred to an electric furnace, and heated from normal temperature to 750 ° C. at a rate of 0.2 ° C./min in a nitrogen atmosphere to be carbonized. This carbide was sieved through a 200 mesh sieve, and the pass product was evaluated as a negative electrode. The results are summarized in Table 1.

(Comparative Example 1) Only the same tar pitch as in Example 2 is heat-treated in an electric furnace and carbonized as in Example 2. Take this out, crush and sieve through a 200 mesh sieve. Table 1 shows the measurement results including the evaluation of the negative electrode using a 200 mesh pass product.

Comparative Example 2 Average particle diameter 10 μm, distance between carbon layers (d ₀₀₂ ) 0.33
Table 1 shows the measurement results, including the evaluation of the negative electrode using 5 nm of natural graphite.

Comparative Example 3 30 parts by weight of the same carbonaceous material (A) as in Example 1 and 90 parts by weight of the same tar pitch as in Example 1 as tar pitch (B) and resol phenol 10 parts by weight of the resin (solid content) and 21 parts by weight of iron oxide (Fe ₂ O ₃ ) in place of the specific metal compound (C) are put into a heating kneader and heated from room temperature to 170 ° C. next,
This is cooled and transferred to an electric furnace, and is cooled to 0.2 in a nitrogen atmosphere.
The temperature is raised from room temperature to 750 ° C. at a temperature rising rate of ° C./min, and carbonized. This carbide is sifted through a 200 mesh sieve,
A 200 mesh pass product was evaluated for the negative electrode. The results are summarized in Table 1.

(Comparative Example 4) The same procedure as in Example 1 was carried out, and the temperature was raised up to 1400 ° C. This was passed through a 200 mesh sieve to evaluate the pass product as a negative electrode. The results are summarized in Table 1.

[0025]

[Table 1]

Comparative Examples 1 to 4 are inferior in discharge capacity to each Example. Comparative Example 1 has a low true specific gravity, Comparative Examples 1 to 3 are inferior in quick chargeability, and Comparative Example 2 is inferior in both quick chargeability and remaining capacity display.

[0027]

According to the present invention, as shown in Examples 1 to 4, a very high discharge capacity with a true specific gravity of 2.0 or more and a natural graphite or more, a rapid chargeability, and a residual capacity display. it is possible to provide a safety excellent anode for a lithium ion secondary battery has a high capacitance comprising a superior carbides particles to sex.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-55-85460 (JP, A) JP-A-51-5314 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02 H01M 4/58 C01B 31/02 101 C04B 35/52

Claims (1)

(57) [Claims] 1. A carbonaceous material (A) having an average particle diameter of 1 to 20 μm and a carbon interlayer distance (d ₀₀₂ ) in the range of 0.335 to 0.340 nm, a tar pitch (B), aluminum, zinc and tin. And one or more compounds (C) of a compound selected from silicon or a compound containing any one of the metal elements, and heat-treating the mixture to obtain a carbide. , including in the carbide (a) 10 to 60 wt%, (B) from carbonaceous of 80 to 20 wt%, the particles of carbide is 2 to 20 wt% metal element derived from the (C)
Negative for lithium ion secondary batteries
Pole .