Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-09-29
2004-10-19
Tsang-Foster, Susy (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
Reexamination Certificate
active
06806003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to nonaqueous electrolyte secondary batteries having positive-electrode active materials and negative-electrode active materials, which intercalate/deintercalate (or are doped/undoped with) lithium, and nonaqueous electrolyte solutions.
2. Description of the Related Art
Nickel-cadmium batteries and lead batteries have been used as secondary batteries for electronic devices. Trends toward higher performance and miniaturization of electronic devices due to advanced electronic technology require secondary batteries having higher energy densities. Since nickel-cadmium batteries and lead batteries have low discharge voltages, increases in the energy densities are limited.
Nonaqueous electrolyte secondary batteries using carbonaceous materials capable of intercalating/deintercalating lithium in negative electrodes and lithium compound oxides in positive electrodes have been vigorously developed instead of the nickel-cadmium batteries and lead batteries, since the nonaqueous electrolyte secondary batteries, called lithium ion batteries, have high discharge voltages and reduced self-discharge, and have prolonged cycle lives.
In these nonaqueous electrolyte secondary batteries, carbonaceous materials such as graphite are used as negative-electrode active materials, Li
x
MO
2
wherein M is at least one transition metal and 0.05<x<1.10 is used as positive-electrode active materials, and LiPF
6
and LiBF
4
are used as electrolytes. As organic solvents for dissolving the electrolytes, propylene carbonate, ethylene carbonate, &ggr;-butyrolactone, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl acetate, methyl propionate, 1,2 -dimethoxyethane, and 2-methyltetrahydrofuran are used.
The nonaqueous electrolyte secondary batteries are suitable as power sources for portable electronic devices. In recent years, compact battery packs including batteries and protective circuits have been frequently used with requirements for reduced sizes and weight. In the batteries in the battery packs, higher capacities at large-current discharging modes are required. In order to fulfill such a requirement, improvements in negative electrodes are essential in addition to improvements in positive electrodes and nonaqueous electrolyte solutions.
Current nonaqueous electrolyte secondary batteries, however, are still unsatisfactory as regards improvements in capacities during large-current discharging modes by improvements in negative electrodes.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a nonaqueous electrolyte secondary battery having satisfactory capacity characteristics during a large-current discharging mode.
According to an aspect of the present invention, a nonaqueous electrolyte secondary battery comprises a positive electrode comprising a positive-electrode active material, a negative electrode comprising a negative-electrode active material, the positive-electrode active material and the negative-electrode active material capable of intercalating/deintercalating lithium, and a nonaqueous electrolyte solution, wherein the negative electrode further comprises carbon fibers and carbon flakes.
The carbon fibers and carbon flakes can be disposed in the interstices between the negative-electrode active material particles in this configuration. Moreover, the carbon fibers improves retention of the nonaqueous electrolyte solution and the carbon flakes disposed between the active material particles improves conductivity (reduces internal resistance). These synergistic effects improve the capacity characteristics of the nonaqueous electrolyte secondary battery. In this nonaqueous electrolyte secondary battery, lithium is smoothly doped or undoped at large-current charge or discharge conditions, resulting in high capacity at the high-current load.
In this nonaqueous electrolyte secondary battery, the content of the carbon fibers in the negative electrode is in a range of preferably 0.02 percent by weight to 5 percent by weight and more preferably 0.5 percent by weight to 4 percent by weight, and the content of the carbon flakes in the negative electrode is in a range of preferably 0.1 percent by weight to 30 percent by weight, more preferably 1 percent by weight to 20 percent by weight, most preferably 1 percent by weight to 10 percent by weight.
Moreover, the ratio by weight of the carbon fibers to the carbon flakes in the negative electrode is in a range of preferably 0.2 to 100 and more preferably 0.4 to 20.
In a preferred embodiment of the present invention, the nonaqueous electrolyte secondary battery comprises an electrode composite in which a positive electrode including a lithium compound oxide as the positive-electrode active material and a negative electrode including a carbonaceous material as the negative-electrode active material are wound with a separator disposed therebetween (called a jelly roll type).
REFERENCES:
patent: 6090506 (2000-07-01), Inoue et al.
patent: 2003/0129494 (2003-07-01), Kaneda et al.
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patent: 2000133267 (2000-05-01), None
patent: WO 99/00001 (1999-01-01), None
Derwent abstract for JP 09-027344 A (publication date of Jan. 1997).*
“Graphite (C)- Classifications, Properties, and Applications of Graphite” [Online]. Azom, 2004 [retrieved on 2004-030-03]. Retrieved from the Internet: <URL: http://www.azom.com/details.asp?ArticleID=1630>.
Hatake Shinji
Nagamine Masayuki
Omaru Atsuo
Yamaguchi Akira
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
Tsang-Foster Susy
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