Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-02-28
2003-01-14
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231400, C429S218100, C423S44500R, C428S408000
Reexamination Certificate
active
06506519
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P11-054459 filed Mar. 2, 1999 which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a secondary battery using a nonaqueous electrolyte solution (hereinafter referred to as a “nonaqueous secondary battery”), a method for making a negative electrode component used in the nonaqueous secondary battery, an apparatus for evaluating a graphite material for the negative electrode component, and an apparatus for making the graphite material.
2. Description of the Related Art
As rapid progress is made in the miniaturization of electronic devices, such as portable phones and notebook personal computers, secondary batteries are required to have higher energy densities.
In conventional secondary batteries, such as lead batteries, Ni—Cd batteries, and Ni—MH batteries, discharge voltages are low and energy densities are insufficient. Lithium secondary batteries are also used in practice, in which metallic lithium, lithium alloys, and carbonaceous materials which can electrochemically occlude and release lithium ions are used as negative electrode active materials, and various positive electrodes are used. The lithium secondary batteries have high output voltages and thus have large energy densities per weight or volume compared to the above conventional batteries.
In the lithium secondary batteries at initial stages, metallic lithium and lithium alloys are used as negative electrodes. A negative electrode using metallic lithium or a lithium alloy is insufficient in charge-discharge efficiency and has a problem in that dendritic lithium is formed. Thus, such negative electrodes are used in practice only in a few specialized fields.
Carbonaceous materials which can electrochemically occlude and release lithium ions have recently been anticipated as negative electrode components and are now coming into use. Negative electrodes using the carbonaceous materials do not have problems inherent in the metallic lithium or lithium alloys, that is, the formation of metallic lithium having a dendritic structure and particularization of the lithium alloy during charge-discharge cycles. Moreover, the carbonaceous materials show high coulomb efficiency; hence, lithium secondary batteries having carbonaceous negative electrodes exhibit superior charge-discharge reversibility.
In secondary batteries using the carbonaceous materials as negative electrode active materials, metallic lithium is not precipitated in use. Thus, lithium secondary batteries using the carbonaceous materials and nonflammable lithium compound oxide are safe and are commercially produced. These batteries are called “lithium ion batteries” and use carbonaceous materials as negative electrodes, LiCoO
2
as positive electrodes, and nonaqueous electrolyte solutions containing nonaqueous solvents.
Carbonaceous materials used as negative electrodes are classified into graphite materials including natural products and artificial products, easily-graphitizable carbonaceous materials as precursors of artificial graphite materials, and ungraphitizable carbonaceous materials which are not converted to graphite even when these are treated at high temperatures facilitating the formation of graphite. Graphite materials and ungraphitizable carbonaceous materials have high capacities as negative electrodes and are thus currently used.
Lithium ion batteries have rapidly gained widespread use as electrical power sources in electronic devices, particularly, notebook personal computers due to compact, because they are lightweight, and have high capacities. Notebook personal computers having improved performance require higher CPU clock frequencies. Thus, high-performance computers consume significant amounts of electrical power and generate substantial amounts of heat during operation. Moreover, the restricted volume of dead space, which is inherent in miniaturization of personal computers, precludes the dissipation of heat which is generated during operation, resulting in an increase in the internal temperatures of personal computers.
The increased temperature accelerates deterioration and thus decreases capacity in batteries used in personal computers. The lost capacity cannot be restored by any means.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a lithium ion secondary battery which does not cause deterioration by generating excessive heat, has high capacity, and is highly reliable in use.
It is another object of the present invention to provide a method for making a negative electrode component used in a nonaqueous secondary battery, an apparatus for evaluating a graphite material as the negative electrode component, and an apparatus for making the graphite material.
According to experimental results obtained by the present inventors, a lithium ion secondary battery using a carbonaceous material for a negative electrode, which has specific structural parameters, can maintain high capacity even after such a battery is stored in high-temperature environments, and has high capacity reliability for long periods.
According to a first aspect of the present invention, a nonaqueous secondary battery includes a negative electrode including a carbonaceous material in which the ratio RG=Gs/Gb of the degree of graphitization Gs of the carbonaceous material, determined by a surface-enhanced Raman spectrum, to the degree of graphitization Gb, determined by a Raman spectrum measured using argon laser light, is at least 4.5, based on the following conditions:
Gb=Hbb/Hba;
and
Gs=Hsb/Hsa;
wherein
Hba is the height of a peak lying in a range of 1,580 cm
−1
to 1,620 cm
−1
in a Raman spectrum which is measured using an argon laser Raman spectrometer of a wavelength of 514.5 nm and a wavelength resolution of 4 cm
−1
;
Hbb is the height of a peak lying in a range of 1,350 cm
−1
to 1,400 cm
−1
in a Raman spectrum which is measured using an argon laser Raman spectrometer of a wavelength of 514.5 nm and a wavelength resolution of 4 cm
−1
;
Hsa is the height of a peak lying in a range of 1,580 cm
−1
to 1,620 cm
−1
in a surface-enhanced Raman spectrum which is measured using an argon laser Raman spectrometer of a wavelength of 514.5 nm and a wavelength resolution of 4 cm
−1
when silver having a thickness of 10 nm is deposited on the carbonaceous material; and
Hsb is the height of a peak lying in a range of 1,350 cm
−1
to 1,400 cm
−1
in a surface-enhanced Raman spectrum which is measured using an argon laser Raman spectrometer of a wavelength of 514.5 nm and a wavelength resolution of 4 cm
−1
when silver having a thickness of 10 nm is deposited on the carbonaceous material.
According to a second aspect of the present invention, a nonaqueous secondary battery includes a negative electrode including a carbonaceous material having a peak in a wavelength range above 1,360 cm
−1
in a surface-enhanced Raman spectrum which is measured using an argon laser Raman spectrometer of a wavelength of 514.5 nm and a wavelength resolution of 4 cm
−1
when silver having a thickness of 10 nm is deposited on the carbonaceous material.
In the nonaqueous secondary battery according to the first aspect and second aspect, the carbonaceous material is preferably graphite.
The nonaqueous secondary battery further includes a positive electrode, which preferably includes a lithium compound oxide represented by LiM
x
O
y
wherein M is at least one element selected from the group consisting of Co, Ni, Mn, Fe, Cr, Al, and Ti.
According to a third aspect of the present invention, a method for making a negative electrode component used in the nonaqueous secondary battery according to the first aspect, includes the steps of carbonizing a raw material, slightly oxidizing the surface of the carbonized material, and then graphitizing the oxidized mater
Kita Akinori
Omaru Atsuo
Satori Kotaro
Alejandro R
Kalafut Stephen
Sonnenschein Nath & Rosenthal
Sony Corporation
LandOfFree
Nonaqueous secondary battery, method for making negative... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nonaqueous secondary battery, method for making negative..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nonaqueous secondary battery, method for making negative... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3056984