JPH04322056A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To obtain a battery of large discharging capacity, and of good charging/discharging cycle characteristic by using spherical carbon particulate having condensed polynuclear aromatic structure as a negative electrode active material. CONSTITUTION:In a battery for which an organic electrolyte in which lithium salt is dissolved in an organic solvent is used, spherical carbon particulate is used for which particles of condensed polynuclear aromatic structure serving as a negative electrode active material that forms a negative electrode 5 is properly cabonated into a crystalline structure similar to graphite. As the carbon particulate has a spherical grain form of normally 1-100mum of average grain diameter, when it is used as negative electrode active material, charging efficiency is improved. The discharging capacity par volume is increased, while charging/discharging characteristic is improved.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] This invention relates to a button-type, cylindrical-type, etc. lithium secondary battery using an organic electrolyte prepared by dissolving a lithium salt in an organic solvent. It is. BACKGROUND OF THE INVENTION In recent years, expectations have been increasing for rechargeable lithium secondary batteries that have a large discharge capacity and can be used for long periods of time at high voltage and energy density. Conventionally, this type of lithium secondary battery uses an organic electrolyte prepared by dissolving a lithium salt in an organic solvent, and uses lithium or a lithium alloy as a negative electrode active material. This caused problems in terms of deterioration of battery characteristics and safety, as internal short circuits were likely to occur. Therefore, instead of lithium or lithium alloy, carbon materials such as activated carbon and graphite can be used as negative electrode active materials, as described in Japanese Patent Application Laid-open No. 58-35881, Japanese Patent Application Laid-Open No. 59-143280, and ``Journal of
"Electrochemical Society", p. 222 (1970), "29th Battery Symposium Abstracts", p. 139 (1988), etc. [Problems to be Solved by the Invention] However, with the above-mentioned known carbon materials, it is difficult to obtain sufficient discharge capacity, and there are problems such as poor charge/discharge cycle characteristics and easy self-discharge. However, it still cannot be said to be fully satisfactory. [0006] In view of the above-mentioned conventional circumstances, it is an object of the present invention to provide a lithium secondary battery that has a large discharge capacity, good charge/discharge cycle characteristics, little self-discharge, and is satisfactory in terms of safety. The purpose is [Means for Solving the Problems] As a result of intensive studies to achieve the above object, the inventors found that by using a carbon material having a specific crystal structure as a negative electrode active material, the discharge capacity can be increased. The present inventors have discovered that a lithium secondary battery can be obtained that has a large capacity, good charge-discharge cycle characteristics, little self-discharge, and is highly safe, leading to the completion of this invention. That is, the present invention uses spherical carbon fine particles having a condensed polycyclic aromatic ring structure as a negative electrode active material in a lithium secondary battery using an organic electrolyte prepared by dissolving a lithium salt in an organic solvent. The invention relates to a lithium secondary battery characterized by: Structure and operation of the invention: The spherical carbon fine particles having a condensed polycyclic aromatic ring structure used in the present invention are those that are used in the present invention when coal-based or petroleum-based heavy oils, tars, or pitches are heated. As the temperature rises, aromatic rings are formed and are gradually converted into molecules with a condensed polycyclic aromatic ring structure.By further heating this material and carbonizing it until it becomes a graphite-like structure, it becomes spherical carbon particles. The average particle diameter is generally in the range of 1 to 100 μm, and the true density is in the range of 1.4 to 2.2. [0010] Here, the molecules of the condensed polycyclic aromatic ring structure before the above carbonization treatment are planar molecules that can serve as electron donors and acceptors, are capable of free movement, and have a small intermolecular distance. In a liquid phase state where the It is known that the structure is spherical in the sexual matrix, and its structure is that the planar molecules described above are stacked, with each lamellar end perpendicular to the spherical surface. [0011] The spherical carbon fine particles can be obtained by carbonizing molecules having such a condensed polycyclic aromatic ring structure, but at this time, as a condition for the carbonization treatment, an appropriate treatment to obtain a crystal structure similar to graphite is required. By selecting the conditions,
Good results can be obtained in improving the discharge capacity and charge/discharge cycle characteristics of a lithium secondary battery using the above-mentioned fine particles as a negative electrode active material, and favorable results can also be obtained in reducing self-discharge. On the other hand, if the carbonization treatment is insufficient to achieve the above structure, the true density will be small, and a lithium secondary battery using this as a negative electrode active material will have a small discharge capacity per volume. Furthermore, since cation intercalation does not occur by simply forming an electric double layer at the interface with the electrolyte, there are no negative effects such as poor charge/discharge cycle characteristics or increased self-discharge. Easy to invite. On the other hand, if the structure exceeds the above, that is, if the carbonization process is excessive to create a complete graphite structure, it will become unstable with respect to the electrolyte, and when cations are taken in, the propylene carbon The problem is that it chemically reacts with the electrolyte such as carbon, reducing its discharge capacity. [0013] When an appropriate carbonization treatment is performed to obtain a crystal structure similar to graphite, the average interplanar spacing of the carbon layer planes is usually 3.
．． 35 Å or more, the crystallite size in the c-axis direction is 500 Å or less, and the crystallite size in the a-axis direction is 700 Å or less,
and 1380 cm-1 for the peak intensity of 1580 cm-1 in the Raman spectrum using an argon laser.
Usually, the ratio of the peak intensity of 1 to 1 is 0.2 or more. Therefore, it is desirable to appropriately select the conditions for carbonization treatment so that such characteristic values can be obtained. By the way, regarding the use of a carbon material having a crystal structure similar to graphite as a negative electrode active material, Japanese Patent Application Laid-Open No. 62-90863 and Japanese Patent Application Laid-Open No. 62-122
As disclosed in JP-A No. 066, JP-A-63-24555, JP-A-1-204361, etc.
It is already publicly known. However, this type of carbon material has a condensed polycyclic aromatic ring structure, which is produced by a method completely different from that of the present invention, such as a solid phase or gas phase carbonization method, but it has a plate-like structure. It takes the form of particles and has the drawbacks of low bulk density and extremely low discharge capacity per volume. On the other hand, the carbon fine particles having a condensed polycyclic aromatic ring structure of the present invention usually have an average particle diameter of 1 to 10
Since it takes the form of spherical particles in the range of 0 μm, when used as a negative electrode active material, the filling rate can be greatly improved, and an excellent discharge reaction without anisotropy can be expected. It is characterized by a marked increase in discharge capacity. When the spherical carbon fine particles of the present invention are used as a negative electrode active material, they can be loaded into a battery as they are, but generally, a molded body of a desired shape containing the above particles is prepared in advance, and then It is preferable to load it inside the battery. To produce a molded body, for example, a slurry is prepared by dispersing the above particles and polytetrafluoroethylene powder as a binder in a water-alcohol mixed solvent, and this is applied onto a wire mesh such as a nickel mesh. After drying, it may be punched out integrally with the wire mesh and then pressure molded to a desired thickness. FIG. 1 shows an example of the structure of a button-shaped lithium secondary battery of the present invention using the above molded body as a negative electrode. In this figure, 1 is a dish-shaped negative electrode can made of stainless steel with nickel plating on the inside, 2 is a dish-shaped cathode can made of stainless steel, and these cans 1 and 2 are placed facing each other.
A flat airtight container is constructed by fitting and press-bonding the peripheral edges of both with an annular gasket 3 made of an elastic insulating material such as synthetic rubber or synthetic resin interposed therebetween. Inside this container, a negative electrode 5 made of the specific molded body bonded to the negative electrode can 1 via a current collector 4 made of stainless steel net, and a current collector 6 made of stainless steel net attached to the positive electrode can 2. The positive electrode 7 and both electrodes 5,
A separator 8 and an electrolyte absorber 9 interposed between the electrodes 7 are loaded, and an organic electrolyte prepared by dissolving a lithium salt in an organic solvent is injected. In the above organic electrolyte, polar solvents such as ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, and dioxolane are used as the organic solvent. In addition, lithium salts include LiCF3 SO3, LiBF4,
LiClO4, LiBφ4 (φ is phenyl group), L
Various salts such as iPF6 and LiAsF6 are used. The present invention is not limited to the illustrated button type battery, but can be applied to lithium secondary batteries of various shapes and structures, including a cylindrical type. As described above, according to the present invention, by using specific spherical carbon fine particles as the negative electrode active material, the discharge capacity is large, the charge/discharge cycle characteristics are good, and self-discharge is reduced. , it is possible to provide a lithium secondary battery with excellent safety. EXAMPLES Next, examples of the present invention will be described in more detail. In the following examples, Mericarbon Microbeads manufactured by Osaka Co., Ltd. were used as spherical carbon particles having a condensed polycyclic aromatic ring structure, but the present invention is not limited to those using the above-mentioned products. Needless to say. Example 1 Mericarbon microbeads with an average particle diameter of 20 μm and a true density of 2.006 (as for the crystal structure, the average spacing between the carbon layer planes is 3.435 Å, and the crystallite size in the c-axis direction is 25Å
, the crystallite size in the a-axis direction is 20 Å or less, and the Raman spectrum using an argon laser is 1580 cm-
The ratio of the peak intensity at 1380 cm to the peak intensity at 1 is 0.9 or more) 30 g, 4.7 g of pure water, aqueous dispersion 1 of polytetrafluoroethylene with a concentration of 60% by weight
．． 5 ml of isopropyl alcohol and 2.8 ml of isopropyl alcohol were placed in a sample bottle and stirred for 30 minutes to form a slurry. This slurry-like material was applied onto a 60-mesh nickel net so that the thickness after drying was 0.4 mm, and the mixture was heated at 200°C.
It was dried for 1 hour. Next, after punching out this into a size of 10 mm in diameter (approximately 0.785 cm2 in area),
Pressure molded at a pressure of ton/cm2, total thickness 0.3m
A molded body of m was produced. The above molded body was used as a negative electrode, and Mn was used as a positive electrode.
A molded body with a thickness of 0.5 mm and a diameter of 10 mm made of a mixture of O2, a microporous polypropylene film as a separator, a polypropylene nonwoven fabric as an electrolyte absorber,
LiCF3 was added to a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1:1 as an organic electrolyte.
A button-shaped lithium secondary battery having the structure shown in FIG. 1 was fabricated using a solution prepared by dissolving 0.6 mol/l of SO3 and using a polypropylene annular gasket. Example 2 As spherical carbon fine particles having a condensed polycyclic aromatic ring structure, meric carbon microbeads with an average particle diameter of 20 μm and a true density of 1.943 (as for the crystal structure, the average interplanar spacing of the carbon layer planes is 3 .481 Å, the crystallite size in the c-axis direction is 22 Å, a
The crystallite size in the axial direction is 20 Å or less, and the ratio of the peak intensity at 1355 cm-1 to the peak intensity at 1580 cm-1 in the Raman spectrum using an argon laser is 0.9 or more). A button-shaped lithium secondary battery was produced in the same manner as in Example 1, except for using the following. Example 3 As spherical carbon fine particles having a condensed polycyclic aromatic ring structure, meric carbon microbeads with an average particle diameter of 20 μm and a true density of 2.15 (as for the crystal structure, the average interplanar spacing of the carbon layer planes is 3
．． 421 Å, the crystallite size in the c-axis direction is 370 Å, a
The crystallite size in the axial direction is 222 Å, and the ratio of the peak intensity at 1355 cm to the peak intensity at 1580 cm in the Raman spectrum using an argon laser is 0.89). A button-type lithium secondary battery was produced in the same manner as in Example 1 except for this. Example 4 As spherical carbon fine particles having a condensed polycyclic aromatic ring structure, meric carbon microbeads with an average particle diameter of 6 μm and a true density of 2.00 (as for the crystal structure, the average interplanar spacing of carbon layer planes is 3 ．．
480 Å, the crystallite size in the c-axis direction is 24 Å, the crystallite size in the a-axis direction is less than 20 Å, and the peak at 1580 cm-1 in the Raman spectrum using an argon laser.
The ratio of the peak intensity at 1355 cm-1 to the peak intensity is 1
．． A button-shaped lithium secondary battery was produced in the same manner as in Example 1, except that 30 g of 09) was used. Comparative Example 1 Instead of using spherical carbon fine particles having a condensed polycyclic aromatic ring structure (average particle diameter 20 μm, true density 2.006), an average particle diameter of 2.
A button-shaped lithium secondary battery was produced in the same manner as in Example 1 except that graphite having a diameter of 0 μm and a true density of 2.25 was used. The relationship between the number of charge/discharge cycles and the discharge capacity of each of the batteries of the above examples and comparative examples was investigated. The results were as shown in Table 1 below. [0030] As is clear from the results in Table 1 above, the lithium secondary battery of the present invention has a large discharge capacity and good charge/discharge cycle characteristics, and can be used as a safe battery with little self-discharge. It can be seen that the above characteristics can be widely applied to various uses.

[Brief explanation of the drawing]

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

[Explanation of symbols]

5 Negative electrode 7 Positive electrode

Claims (3)

[Claims] [Claim 1] A lithium secondary battery using an organic electrolyte prepared by dissolving a lithium salt in an organic solvent, characterized in that spherical carbon fine particles having a condensed polycyclic aromatic ring structure are used as a negative electrode active material. Lithium secondary battery. [Claim 2] The spherical carbon fine particles have an average particle diameter of 1
~100 μm and true density of 1.4 to 2.2. Claim 1
lithium secondary battery. 3. The spherical carbon fine particles have an average interplanar spacing of carbon layer planes of 3.35 Å or more, a crystallite size in the c-axis direction of 500 Å or less, and a crystallite size in the a-axis direction of 700 Å or less, and 13 for the peak intensity at 1580 cm in the Raman spectrum using an argon laser.
The lithium secondary battery according to claim 1 or 2, having a crystal structure in which the ratio of peak intensities at 80 cm-1 is 0.2 or more.