Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-03-10
2004-05-04
Ryan, Patrick (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S231800
Reexamination Certificate
active
06730135
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is based on application No. 98-7854 filed in the Korean Industrial Property Office on Mar. 10, 1998, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to and an active negative material for lithium secondary battery, a method of preparing the same and a lithium secondary battery using the same, and more particularly, to an active negative material useful for fabricating a lithium secondary battery having a high capacity.
(b) Description of the Related Art
In recent years, the development of miniaturized portable electronics provokes needs for a secondary battery having a high capacity as well as a light weight. From the viewpoint of the capacity improvement per unit weight, the lithium secondary battery is preferably adopted because lithium has a high standard potential as well as a low electrochemical equivalent weight.
FIG. 1
is a schematic cross sectional view showing the general structure of the coin-typed lithium secondary battery. As shown in
FIG. 1
, the lithium secondary battery includes a positive electrode plate
40
having a collector
1
made of nickel and an active material layer
10
coated on the collector
1
, a negative electrode plate
45
having a collector
1
′ made of copper and an active material layer
30
coated on the collector
1
′, and a separator
25
interposed between the positive and negative electrode plate
40
and
45
. The positive and negative electrode plates
40
and
45
essentially form an electrode plate assembly together with the separator
25
. The electrode plate assembly is inserted into an opening portion of a battery case
5
internally surrounded with a gasket
20
while receiving an electrolyte
15
therein. The opening portion of the battery case
5
is covered by a cap
35
.
FIG. 2
is a schematic cross sectional view showing the general structure of the cylindrical-typed lithium secondary battery. As shown in
FIG. 2
, the lithium secondary battery includes positive electrodes
50
, negative electrodes
55
stacked in order and separated by a separator
60
. The layered structure is wound a number of times in a spiral form to obtain an electrode winding body. The electrode winding body is inserted into a battery can
90
including nickel plated steel insulating plates
80
,
85
respectively inserted into the top and bottom of the battery can
90
. For the purpose of collecting electricity of the negative electrode, one end of a nickel negative lead
75
is pressure-connected to the negative electrode, and the other end thereof is welded to the battery can
90
. In addition, in order to collect electricity of the positive electrode, one end of an aluminum positive electrode lead
70
is attached to positive electrode
50
, and the other end is welded to battery cover
100
having current interrupting mechanism
105
.
Lithium-containing transitional metal oxide such as LiCoO
2
, LiNiO
2
, LiMn
2
O
4
and LiNi
x
Co
1-x
O
y
are preferably selected for the positive electrode active materials in conjuction with a polyethylene-based porous film for the separator.
As for the negative electrode active materials, lithium metal is attractive because it has a light weight and high capacity per unit weight to thereby output high voltage in the battery use. However, the use of lithum metal for the negative electrode material reveals serious defects in a cycle life and stability of the battery because the lithium metal is highly reactive with the electrolytic solvent and easily forms needle dendrites during cyciling, casusing destruction of the separator and a short circuit. In order to avoid the defects, lithium alloys are employed as the negative electrode active material instead of the lithium metal but yet reveals similar problems.
Alternatively, carbon materials, which can reversibly accept and donate significant amounts of lithium without affecting their mechanical and electrical properties, are proposed for the negative electrode active material.
The carbon materials adapted for use in a battery are generally spherical type carbon materials and fiber type carbon materials. A method for preparing the spherical type carbon material is disclosed in Japanese Patent No. Hei 1-27968. In the method, a coal tar pitch is heat-treated and centrifuged to thereby produce small spherical particles having an optical anisotropy (referred to hereinafter more simply as mesophase particles). Alternatively, a coar tar pitch is centrifuged to obtain supernatant and the supernatant is heat-treated, obtaining mesocarbon microbeads.
However, the aforementioned techniques are not economical and the manufacturing process is complicate because the centrifugation step should performed for obtaining mesophase particles. Furthermore, mesophase particles is only used for preparing spherical carbon materials, the total yield is low.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a negative active material useful for fabricating a lithium secondary battery having a high capacity.
It is another object of the present invention to provide a method of preparing the negative active material with simple manufacturing process and high yield.
It is another object of the present invention to provide a lithium secondary battery using the negative active material.
In order to achieve this object and others, the present invention provides a negative active material including a graphite-like carbon material having an intensity ratio I(110)/I(002) of an X-ray diffraction peak intensity I(002) at a (002) plane to an X-ray diffraction peak intensity I(110) at a (110) plane of less than 0.2. The negative active material is prepared by dissolving a coal tar pitch or a petroleum pitch in an organic solvent to remove insoluble components therefrom, heat-treating the pitch at a temperature in the range of 400 to 450° C. for four hours or more to thereby produce at least 50 weight percent of mesophase particles based on the pitch, coking the pitch including the mesophase particles, carbonizing the coked pitch, pulverizing the carbonized pitch and graphitizing the pulverized pitch.
The lithium secondary battery includes a negative electrode having the negative active material, a positive electrode having a lithium containing material that can reversibly intercalate and de-intercalate lithium ion and a non-aqueous electrolyte.
REFERENCES:
patent: 4978600 (1990-12-01), Suzuki et al.
patent: 5688483 (1997-11-01), Zhang et al.
patent: 5721071 (1998-02-01), Sonobe et al.
patent: 5906900 (1999-05-01), Hayashi et al.
patent: 5932373 (1999-08-01), Nagamine et al.
patent: 6139990 (2000-10-01), Kubota et al.
patent: 6245460 (2001-06-01), Choi et al.
B.D. Culity, Elements of X-ray Diffraction, 2nd ed. 1978 (no month). p. 401.
Choi Wan-uk
Sheem Kyou-yoon
Yoon Sang-young
Blakely & Sokoloff, Taylor & Zafman
Dove Tracy
Ryan Patrick
Samsung Display Devices Co. Ltd.
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