Carbon material for negative electrode of secondary lithium batt

Details Carbon material for negative electrode of secondary lithium batt Carbon material for negative electrode of secondary lithium batt

1999-01-25

2000-12-05

Jones, Deborah

Stock material or miscellaneous articles

Self-sustaining carbon mass or layer with impregnant or...

423448, 423445R, 4292314, 4292318, B32B 6900, H01M 448

Patent

active

06156432&

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a negative electrode for lithium secondary battery, a negative electrode material therefor (a graphite material and a carbon material coated with a low-crystalline carbon), and a process for preparing the same. More specifically, the invention relates to a negative electrode for a lithium secondary battery having a high discharge capacity as well as a high initial efficiency, a negative electrode material therefor, and a process for preparing the same. The present invention also relates to a nonaqueous lithium secondary battery and a solid-electrolyte lithium secondary battery.


BACKGROUND ART

With regard to lithium secondary batteries in which graphite is used, there are a number of patent applications, including Japanese Unexamined Patent Publication No.57-208079 (Japanese Examined Patent Publication No.62-23433). However, the theoretical capacity of graphite as calculated from the composition LiC.sub.6 is considered 372 Ah/kg (carbon basis). The theoretical capacity of graphite as a host for lithium is also 372 Ah/kg (carbon basis). Thus, there has been a limit to discharge capacity.
However, the electronic device industry uninterruptedly demands conspicuous improvements in battery performance. To meet the requirements for high performance battery, significant improvements in the properties of the negative electrode to be used in the lithium secondary battery are essential. In view of the situation, the capacity of 372 Ah/kg cannot be considered sufficiently high in terms of negative electrode capacity.
Therefore, the modification of graphite-based intercalation compound heretofore-proposed is not enough to attain the needed lithium storage capacity.
The object of the present invention, in consideration of the above state of the art, is to provide a lithium secondary battery having a charge/discharge capacity exceeding the theoretical capacity of 372 Ah/kg and to provide negative electrode useful in the a lithium secondary battery, a negative electrode material, and a process for preparing a carbon material therefor.


DISCLOSURE OF INVENTION

Under the circumstances, the present inventors made intensive researches and found that when pores are intentionally formed in the crystal structure of graphite to be used as a negative electrode material for lithium secondary batteries, though the initial efficiency falls, unexpectedly, the charge/discharge capacity increases; that when said graphite is coated with a low-crystalline carbon, the fall in initial efficiency can be mitigated; and that a carbon material comprising carbon particles or aggregated carbon particles and having the surface coated with a low or moderately crystalline carbon can be produced by immersing a graphite material, which is to serve as the core material, in a carbonizable organic compound, such as tar or pitch, and then carbonizing the same.
The present invention provides a graphite material, a carbon material, a process for preparing said carbon material, a negative electrode material for lithium secondary battery, a negative electrode for lithium secondary battery, and a lithium secondary battery, as specified below. diffractometry for the plane (002) is not more than 0.336 nm; than 0.019: ##EQU1## where D represents the density, c.sub.0 and Lc represent the lattice constant and crystallite size, respectively, in the direction of c axis, a.sub.0 and La represent the lattice constant and crystallite size, respectively, in the direction of a axis, and the superscript "i" represents the value for an ideal graphite; the density value is the value obtained by the method according to JIS R 7212 and the crystallite size value is the value obtained by the method established by the Japan Society for the Promotion of Science; characterized in that the surface of the graphite material defined in paragraph 1 above is coated with a coat-forming carbon material. characterized in that the surface of the graphite material as defined in paragraph 1 above is coated with a double-layer structure for

REFERENCES:
patent: 5244757 (1993-09-01), Takami et al.
patent: 5667914 (1997-09-01), Nagamine et al.
patent: 5698341 (1997-12-01), Tamaki et al.
patent: 5753387 (1998-05-01), Takami et al.
patent: 5932373 (1999-08-01), Nagamine et al.

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