JP3310695B2 - Carbon electrode and lithium secondary battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon electrode and a lithium secondary battery using the same.

[0002]

BACKGROUND ART Echirenka - BONNET - in a lithium secondary battery in which an organic solvent by dissolving a lithium salt such as LiCF ₃ SO ₃ in the organic electrolyte solution, such bets, those using lithium or a lithium alloy for the negative electrode, Internal short circuits easily occur, and there are problems in terms of battery characteristics deterioration and safety.

For this reason, it has been proposed to use a carbonaceous material such as activated carbon or graphite as a negative electrode carrier in place of lithium or a lithium alloy as disclosed in JP-A-57-208079, JP-A-58-35881 and JP-A-58-35881. Showa 59-143280
Publication, “Journalof Electroche
Medical Society ", p. 222 (1970)
), "The 29th Battery Symposium Abstracts", p. 139 (1988).

Japanese Patent Application Laid-Open No. 62-122066 discloses that the atomic ratio of hydrogen / carbon is less than 0.15, and the (002) plane spacing determined by wide-angle X-ray diffraction is 3.37 ° or more. It has been proposed to use a carbonaceous material having a graphite-like structure having a crystallite size of 150 ° or less in the c-axis direction as a negative electrode carrier of a nonaqueous solvent battery.

When a negative electrode using lithium as an active material with such a carbonaceous carrier as a carrier is used, the volume energy density is sacrificed to some extent as compared with a battery using a lithium or lithium alloy plate as a negative electrode. The reversibility and safety of charging and discharging are dramatically improved. It is also known that the use of the carbonaceous material having a graphite-like structure gives good results in suppressing self-discharge and improving cycle characteristics.

[0006]

However, in the lithium secondary battery using the above-mentioned carbonaceous material as the negative electrode carrier, there is a problem that the polarization is large and the capacity becomes small during heavy load charging and discharging.

The present invention solves the above-mentioned problems of the conventional carbonaceous material, and provides a lithium secondary battery having good load characteristics, and a carbon electrode for a negative electrode which enables this. The purpose is.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, they have been obtained by providing a specific coating layer on carbonaceous material having a structure similar to conventional graphite and heat-treating it. When a carbonaceous material was used as a negative electrode carrier, it was found that a high-capacity lithium secondary battery could be obtained even during heavy load charging and discharging, and the present invention was completed.

That is, a first aspect of the present invention relates to a particulate matter of a carbonaceous or organic polymer having a graphite-like structure .
And 5 to 30 Ri Do from the molded body of the carbonaceous material formed by heat treatment or carbonization treatment provided volume% of the pitch coating layer, and electrostatic
Mosquitoes for a lithium secondary battery gas resistivity and wherein ^{7.0 × 10 -3 ~5.0 × 10 -2} Ωcm der Rukoto - are those according to the Bonn electrode, also, the of the invention No. 2 relates to a lithium secondary battery using an organic electrolyte obtained by dissolving a lithium salt in an organic solvent, wherein the carbon electrode is used as a negative electrode. .

[0010]

The carbonaceous material having a graphite-like structure according to the present invention is a carbonaceous material capable of doping and undoping lithium ions. Carbon fiber, activated carbon, or the like can be used. Further, as the organic polymer substance, a resin which is solid at room temperature, such as a phenol resin, a polyacrylonitrile resin, a cellulose resin, a polyamide resin, a polyamideimide resin, and a vinyl halide resin, can be widely used.

The average particle diameter of the particulate matter composed of such a carbonaceous or organic polymer substance is preferably about 5 to 100 μm. Since the electrical resistivity of the particulate matter is generally not sufficiently small, the lithium secondary battery using this as a negative electrode support has a large polarization during heavy load charging and discharging, and thus has a reduced capacity.

In the present invention, in order to overcome the above-mentioned problems, a pitch coating layer is provided on the surface of the above-mentioned particulate matter, and this is heat-treated or carbonized to form a carbonaceous material. Itself has a low electric resistivity (volume resistivity). Therefore, a lithium secondary battery using this as a negative electrode support has reduced polarization during heavy load charging and discharging, and has a capacity similar to that of a conventional battery. Reduction is suppressed.

When a lithium secondary battery is manufactured by mixing metal powder or the like as a conductive additive with a carbonaceous material having a conventional structure and using this as an electrode material, polarization during heavy load charging and discharging is small. Although the capacity is increased, metal powder and the like do not participate in the doping and dedoping reactions of lithium. No effect.

In the present invention, the formation of the pitch coating layer is carried out by removing a carbon black solid residue obtained by distilling a tar formed by the dry distillation of an organic substance, for example, a coater. -Pitch, such as wood pitch, wood pitch, etc., may be applied, and the applied amount may be usually about 5 to 30% by volume based on the particulate matter.

After the formation of the coating layer, it is usually 800 to 2.5
The target carbonaceous material can be obtained by heat treatment at a temperature of about 00 ° C., or when the particulate matter is made of an organic polymer substance, particularly by carbonizing it at the same temperature as described above.

The carbon electrode of the present invention is obtained by using the carbonaceous material thus obtained into a molded article having a desired shape by a conventional method. As an example, a slurry is prepared by dispersing the above-mentioned carbonaceous material powder and polytetrafluoroethylene powder as a binder thereof in a water-alcohol-based mixed solvent, and applies this to a wire mesh such as a nickel mesh. ,
After drying, and then punching and forming it integrally with the above-mentioned wire mesh, pressure forming may be performed until a desired thickness is obtained.

FIG. 1 shows an example of the structure of a button-type lithium secondary battery of the present invention using the above-mentioned carbon electrode as a negative electrode. In the figure, reference numeral 1 denotes a dish-shaped negative electrode can made of stainless steel, and 2 denotes a dish-shaped positive electrode can made of stainless steel. By fitting and crimping with an annular gasket 3 made of an elastic insulating material of
It has a flat closed container.

Inside the container, a negative electrode 5 made of the specific molded body joined to the negative electrode can 1 via a current collector 4 made of stainless steel, and a current collector 6 made of stainless steel in the positive electrode can 2 And the positive and negative electrodes 7 and 5
A separator 8 and an electrolytic solution absorber 9 interposed between 7 are mounted, and an organic electrolytic solution obtained by dissolving a lithium salt in an organic solvent is injected.

In the above-mentioned organic electrolyte, ethylene carbonate and propylene carbonate are used as the organic solvent.
1,2-dimethoxyethane, γ-butyrolactone,
A polar solvent such as dioxolane is used. As the lithium salt, LiCF ₃ SO ₃ , LiBF ₄ , Li
ClO ₄ , LiBφ ₄ (φ is a phenyl group), LiP
Various salts such as F ₆ and LiAsF ₆ are used.

It is needless to say that the negative electrode comprising the carbon electrode of the present invention is not limited to the button type battery shown in the drawings, but can be applied to lithium secondary batteries of various other forms and structures such as cylindrical ones.

[0021]

As described above, a lithium secondary battery having good load characteristics can be obtained by using the carbon electrode formed of the specific carbonaceous material compact of the present invention as a negative electrode. .

[0022]

Next, an embodiment of the present invention will be described in more detail.

Example 1 Coal pitch was applied to a spherical phenol resin having an average particle diameter of 10 μm at a ratio of 20% by volume to the above resin, and then carbonized at 1,000 ° C. Quality material was obtained.

To 30 g of the carbonaceous material, 4.7 g of pure water,
1.5 ml of a 60% by weight aqueous dispersion of polytetrafluoroethylene powder and 2.8 ml of isopropyl alcohol were added, and the mixture was stirred for 30 minutes to form a slurry, which was dried on a 60 mesh nickel mesh. It was applied to a thickness of 0.4 mm and dried at 200 ° C. for 1 hour. This is punched out to a size of 10 mm in diameter (area 0.785 cm ² )
A carbon electrode made of a compact having a total thickness of 0.3 mm was produced by press molding at 10 ton / cm ² .

Next, the above carbon electrode is used as a negative electrode,
A molded product of LiMnO ₂ mixture having a thickness of 0.5 mm and a diameter of 10 mm is used as a positive electrode, a microporous polypropylene film is used as a separator, a polypropylene nonwoven fabric is used as an electrolyte absorber, and ethylene carbonate is used as an organic electrolyte. And 1
A solution obtained by dissolving 0.6 mol / l of LiCF ₃ SO ₃ in a mixed solvent having a volume ratio of 1: 1 with 2-dimethoxyethane, and a cyclic gasket made of polypropylene;
A button-type lithium secondary battery having the structure shown in FIG. 1 was manufactured by using each of them.

Example 2 Coal pitch was applied to a spherical phenolic resin having an average particle diameter of 10 μm at a ratio of 10% by volume to the above resin, followed by carbonization at 1,000 ° C. Quality material was obtained. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used, and a button-type lithium secondary battery having the structure shown in FIG. A secondary battery was manufactured.

Example 3 Coal pitch was applied to a spherical phenolic resin having an average particle diameter of 10 μm at a ratio of 5% by volume to the above resin, and then carbonized at 1,000 ° C. Quality material was obtained. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used, and a button-type lithium secondary battery having the structure shown in FIG. A secondary battery was manufactured.

Comparative Example 1 A spherical phenol resin having an average particle diameter of 10 μm was prepared in 1,000
The carbonized material was carbonized at ° C. to produce a carbonaceous material. Using this material, a carbon electrode was produced in the same manner as in Example 1, and this electrode was used as a negative electrode in the same manner as in Example 1 as shown in FIG. A button-type lithium secondary battery having a structure was manufactured.

Example 4 A polyacrylonitrile system having an average particle diameter of 10 μm (hereinafter referred to as “polyacrylonitrile”)
PAN-based) carbon fiber (1,000 ° C carbonized product)
20% by volume of coal pitch, based on the carbon fiber
, And heat-treated at 1,000 ° C to obtain a carbonaceous material. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used, and a button-type lithium secondary battery having the structure shown in FIG. A secondary battery was manufactured.

Example 5 PAN-based carbon fibers having an average particle diameter of 10 μm (1,000 ° C.)
Coal pitch is applied to the above carbon fiber at a rate of 10% by volume, and then heated at 1,000 ° C.
The treatment resulted in a carbonaceous material. A carbon electrode was prepared in the same manner as in Example 1 except that this carbonaceous material was used.
Further, in the same manner as in Example 1 except that this electrode was used as a negative electrode, FIG.
A button-type lithium secondary battery having the structure shown in FIG.

Comparative Example 2 PAN-based carbon fibers having an average particle diameter of 10 μm (1,000 ° C.)
(Carbonized product) is further heat-treated at 1,000 ° C. to obtain a carbonaceous material. Using this material, a carbon electrode is produced in the same manner as in Example 1, and this electrode is used as a negative electrode in the same manner as in Example 1. Thus, a button-type lithium secondary battery having the structure shown in FIG. 1 was produced.

The electrical resistivity ρ 電極 of each of the carbon electrodes of Examples 1 to 5 and Comparative Examples 1 and 2 was examined. Further, for each of the lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2, 0.5 mA / cm ² and ² mA / cm ²
The discharge capacity when charging and discharging at a constant current of cm ² was measured.
The results are shown in Table 1 below. The above electric resistivity ρ の was measured by the following method.

<Measurement of electrical resistivity ρ∞ of carbon electrode>
After vacuum drying the measurement sample at 150 ° C. for 3 hours, the following formula (1),
As shown in (2), the resistivity ρ with respect to the compression pressure P was measured, and P was extrapolated to infinity from the plot of 1 / {P vs. ρ to determine the electrical resistivity ρ}.

Σ _d = 2√P / (√πH × σ _v ) (1) σ _d = r _c ′ / r × σ _v (2) (when P → ∞, σ _d = σ _v ) σ _d : Apparent conductivity (Scm ^-1 ) σ _v : Conductivity of the substance of the particle (Scm ^-1 ) P: Compression pressure (Kg / cm ² ) H: Hardness of the substance of the particle _rc ': Effectiveness of the contact surface radius _{= r c + Δr c (cm} ) Δr c: increase of the contact circle radius r _c caused by adsorption of moisture to the contact portion (cm)

[0035]

[Table 1]

As is clear from the above test results, each of the lithium secondary batteries of Examples 1 to 3 and Examples 4 and 5 of the present invention correspond to the corresponding conventional Comparative Examples 1 and 2, respectively. It can be seen that the load characteristics are superior to the lithium secondary batteries.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a lithium secondary battery of the present invention.

[Explanation of symbols]

 1: Negative electrode can 2: Positive electrode can 5: Negative electrode 7: Positive electrode 8: Separator 9: Electrolyte absorber

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-94838 (JP, A) JP-A-5-159771 (JP, A) JP-A-5-217604 (JP, A) JP-A-5-217604 307959 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01B 4/02-4/62

Claims (2)

(57) [Claims] 1. A ne from the molded body of the carbonaceous material formed by heat treatment or carbonization treatment provided pitch coating layer of the particulate material in against 5-30 volume% of the carbonaceous or organic polymeric material having a graphite-like structure And the electrical resistivity is 7.0 × 10 ⁻³ or more.
5.0 The lithium secondary to × 10 ^-2 [Omega] cm der wherein Rukoto
Carbon electrode for secondary battery . 2. A lithium secondary battery using an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent, wherein the carbon electrode according to claim 1 is used as a negative electrode. battery.