JPH0582132A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To improve an initial capacity and a cycle service life by transforming a carbonic material having a (n) type dope ability being used as a negative electrode into a material having a crystal structure in which carbon atom bonded polyhedral spherical molecules are arrayed. CONSTITUTION:A negative electrode 2 is composed of a rubber type crystallizing agent and carbon powder having a crystal structure in which polyhedral spherical molecules C60 are arrayed, and is brought into a pressure contact with a negative electrode current collecting body 6 of nickel net. A positive electrode 1 is composed of a positive electrode active material LiCoO2, carbon black and a a binding agent of fluorocarbon type resin, and is press-fitted to a positive electrode current collecting body 5 of aluminium net, and is arranged opposite to the negative electrode 2 through a separator 3. Thereby, a battery, whose self discharge quantity is small and which has a high capacity and has an excellent cycle performance, can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery using a non-aqueous solvent type electrolyte, and more particularly to a carbonaceous material used for its negative electrode.

[0002]

2. Description of the Related Art In recent years, rechargeable batteries using lithium as a negative electrode have been receiving attention, and technological developments for practical use have been vigorous. However, the secondary battery using metallic lithium as the negative electrode has a problem of short charge / discharge cycle life. This is due to the deterioration of the negative electrode due to the dendrite-like deposition of lithium during charging. In order to solve this problem, a lithium secondary battery having a negative electrode of carbon powder or carbon fiber having a lithium storage capacity is disclosed in JP-A-62-2680.
No. 58, etc.

[0003]

However, in the conventional carbon powder or carbon fiber, the lattice spacing (d00) by X-ray diffraction is used.
2) is 3.40 to 3.60Å, and the crystallite size (La, Lc) in the a-axis and c-axis directions is 10 to 250Å, and the initial capacity and cycle of the battery using this are adopted. Regarding the life, satisfactory performance was not obtained.

[0004]

In order to solve the above problems, the present invention is a non-aqueous secondary battery using a carbonaceous material having an n-type doping ability for a negative electrode, wherein the carbonaceous material is
The lithium secondary battery is characterized by having a crystal structure in which polyhedral spherical molecules in which 60 or more carbon atoms are bonded are arranged. As the carbonaceous material having a crystal structure in which polyhedral spherical molecules in which 60 or more carbon atoms are bonded in the present invention are arranged, polyhedral spherical molecules are C ₆₀ , C
₇₀ , C _{76 and the} like, and those having a functional group such as hydrogen or a methyl group bonded to the surface thereof can be used.

[0005]

Embodiments of the present invention will be described below with reference to the drawings.

(Invention) FIG. 1 is a schematic view of a lithium secondary battery according to the present invention. Reference numeral 1 is a positive electrode comprising a positive electrode active material LiCoO ₂ , carbon black as a conductive agent, and a binder of a fluorine-based resin. It is pressure-bonded to the positive electrode current collector 5 of the net. Reference numeral 2 denotes a carbon negative electrode according to the present invention, which is composed of carbon powder having a crystal structure in which polyhedral spherical molecules C ₆₀ are arranged and a rubber binder, and is pressure-bonded to a nickel net negative electrode current collector 6. 3 is a separator made of a polypropylene microporous membrane. Reference numeral 4 is an electrolyte, which is prepared by dissolving LiBF ₄ in γ-butyrolactone. This battery of the present invention is referred to as Battery A.

(Comparative Example) Instead of the negative electrode carbonaceous material of the battery A, the lattice spacing (d002) is 3.46Å, a-axis and c
A battery was produced using carbon powders having crystallite sizes in the axial direction of 25 and 19Å, respectively. This conventional battery is referred to as Battery B.
And The structure of Battery B was the same as that of Battery A except for the negative electrode.

The above-mentioned initial capacities of batteries A and B and charge / discharge efficiency were compared. The results are shown in Table 1. As the test method at this time, the charging was constant current constant voltage charging, the constant current current density was 1 mA / cm ² , and the final voltage was 4.
The constant voltage charging at 2V was performed at a voltage of 4.2V for 5 hours.
The discharge is constant current discharge, the current density is 1 mA / cm ² ,
The final voltage was 3.0V.

[0009]

From Table 1, it has been found that the battery A of the present invention is far superior to the conventional battery B in initial capacity and charge / discharge efficiency. Furthermore, the batteries A and B were charged and the self-discharge amount when left at room temperature for 30 days was investigated. The results are shown in Table 2.

[0011]

From Table 2, it is found that the battery A of the present invention has a smaller self-discharge amount than the conventional battery B. Also,
The relationship between the number of charge / discharge cycles and the discharge capacity of the batteries A and B was investigated. The result is shown in FIG. From FIG. 2, the capacity of the battery A is almost unchanged after 100 cycles, but the capacity of the battery B is 50 cycles and the initial capacity is 5%.
It was found to have dropped to 0%.

[0013]

INDUSTRIAL APPLICABILITY As described above, the present invention can provide a lithium secondary battery having a high capacity, excellent cycle performance, and a small self-discharge, so that its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic view of a lithium secondary battery of the present invention.

FIG. 2 is a relationship diagram between the number of charge / discharge cycles and the discharge capacity of the battery A of the present invention and the battery B of the related art.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 Electrolyte solution 5 Positive electrode current collector 6 Negative electrode current collector

Claims (1)

[Claims] 1. A non-aqueous secondary battery using a carbonaceous material having an n-type doping ability for a negative electrode, the carbonaceous material comprising:
A lithium secondary battery having a crystal structure in which polyhedral spherical molecules having carbon atoms are arranged.