Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
1999-09-09
2001-05-15
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C423S447300
Reexamination Certificate
active
06231829
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the development of an active material useful for an anode of lithium ion secondary cells.
2. Description of Prior Arts
Most commercially available rechargeable lithium ion batteries adopt highly ordered carbonaceous materials as active materials for their anodes. Generally, highly ordered carbonaceous materials are those which have a crystal lattice Lc(002)≧50 Å with a distance between carbon layer planes d
002
≦3.4 Å. Showing a Coulomb effect with a low flat potential curve upon discharging in addition to being low in moisture content and relative impurity content, they are known to be easily applicable in practical processes. Where cost is an important determinant in commercializing the highly ordered carbonaceous materials, they are very disadvantageous in that they are decomposed by reaction to electrolytes and need a high temperature treatment and a high purification treatment. What is worse, they have a theoretical discharge capacity as low as 372 mAhg
−1
. Therefore, there remains a need to develop novel carbonaceous materials which have a larger discharge capacity for high capacity rechargeable batteries.
Recently, there have been reported many research results on carbonaceous materials of low crystallinity which have a higher capacity than the theoretical charge and discharge capacity of the highly ordered carbonaceous materials. Particularly, hard carbons, although suffering from a low initial Coulomb effect and a difficult charging process, attract scientific attention by virtue of their higher electric capacity (400
~
650 mAhg
−1
) than the theoretical value of graphite, low reactivity with electrolytes, and low production cost according to relatively low temperature treatment.
Yoshino et al., prepared a carbonaceous material for lithium ion secondary cells by the pyrolysis of benzene gas. Dahan et al., reported that a disordered carbonaceous material with a high capacity could be prepared by doping boron (B) through a chemical vapor deposition (CVD) process. As for carbonaceous materials prepared by vapor deposition, thus far, most of them are of pyrolyzed carbons deposited on substrates. In fact, because only a very small quantity of carbonaceous materials are deposited through thermal CVD, they are very disadvantageous in productivity and production cost when using them as active materials for the anodes of lithium ion batteries.
There are reports regarding the preparation of carbonaceous materials for anodes of lithium ion rechargeable batteries from solid phase carbon-containing precursors through thermal treatment. For example, polyparaphenylene (Sato et al.), coal-tar pitch (Mabuchi et al.), a phenolic resin (Yara), and sugar carbon (Xing and Xue) are subjected to thermal treatment to produce disordered carbonaceous materials of high charge and discharge capacity. Also, it is reported that various solid phase precursors, such as petroleum pitch, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyphenylene sulfide (PPS), and epoxy novolac resin (ENR), can be thermally treated to produce disordered carbonaceous materials which show largely two charging and discharging properties depending on the precursors. Particularly, when the carbonaceous materials prepared are of hard carbon, they are reported to be more suitable as active materials for anodes of lithium ion rechargeable batteries. However, since the solid thermal treatment process for the preparation of carbonaceous materials has fewer controllable parameters than have vapor deposition processes, it suffers from disadvantages in that it is inconvenient to conduct the structure control of carbonaceous materials, and it is very difficult to add other elements and to control their amounts.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the problems encountered in prior arts and to provide a carbonaceous material for the anode of lithium ion rechargeable batteries, which is superior to highly ordered carbonaceous materials in charge and discharge capacity and properties.
It is another object of the present invention to provide a method for preparing such a carbonaceous material.
It is a further object of the present invention to provide an apparatus in which the preparation of such a carbonaceous material can be achieved.
In accordance with an aspect of the present invention, there is provided a carbonaceous material for anodes of lithium ion rechargeable batteries, which is the soot produced from liquified propane gas through thermal decomposition by a vapor deposition process.
In accordance with another aspect of the present invention, there is provided a method for preparing a carbonaceous material for anodes of lithium ion rechargeable batteries, comprising the steps of: heating a reaction tube to a temperature of 800
~
1,300° C. with argon gas flowing in the reaction tube; introducing 10
~
100% propane gas provided to the reaction apparatus as liquefied propane, into the reaction tube, in which the propane gas is thermally decomposed for 1 to 5 hours while the temperature is maintained; and cooling the reaction tube by introducing argon gas into the reaction tube.
In accordance with a further aspect of the present invention, there is provided an apparatus for preparing a carbonaceous material for anodes of lithium ion rechargeable batteries, comprising a reaction tube flanked by flanges, in which propane gas is thermally decomposed into carbon atoms or molecules and hydrogen atoms and molecules and the carbon atoms are subjected to homogeneous nucleation to produce soot; a furnace for heating the reaction tube; a thermostat for controlling the temperature of the reaction tube through a heat wire; a soot getter for collecting the soot; two drying chambers in which liquified propane gas and argon gas are dried, respectively, before being introduced into the apparatus; two flow meters for respectively controlling the flow and composition of the propane gas and the argon gas which come from the drying chambers; an inlet valve through which the propane gas and the argon gas are mixed; and a pressure gauge for monitoring the pressures of the propane gas and argon gas just before being introduced into the reaction tube.
Based on the fact that a large quantity of soot is generated when hydrocarbons are thermally cracked, the present invention is designed as a soot getter in which the soot can be recovered at a maximal efficiency. While passing through a reaction zone in the center of a furnace, hydrocarbon gases are thermally decomposed into carbon atoms (or molecules) and hydrogen atoms (or molecules). Meanwhile, the carbon atoms (or molecules) of a gas phase react with each other to cause homogeneous nucleation, aggregating to droplets. As they go from the reaction zone to an exhaust outlet, they get gradually larger and finally, are accumulated in particle forms. If the soot particles are not grown sufficiently until they reach the exhaust outlet, they are drained out through the outlet. In the present invention, a soot getter is mounted to an end portion of the reaction tube, that is, to the exhaust outlet, in order to recover the soot particles.
Soot, which is usually produced at a large amount upon the thermal decomposition of hydrocarbons, is of disordered carbon as well as of isotropic carbon and hard carbon. With these properties, soot can be used as an active material for the anode of lithium ion rechargeable batteries, which shows superb electrode properties and far greater specific capacity than do graphite materials usually used.
REFERENCES:
patent: 5500200 (1996-03-01), Mandeville et al.
patent: 5877110 (1999-03-01), Snyder et al.
Han Young Soo
Jang Kuk Jin
Kang Yun Sun
Kim Hae Yeol
Lee Jai Young
Hendrickson Stuart L.
Korea Advanced Institute of Science and Technology
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