Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-01-04
2004-07-20
Bos, Steven (Department: 1754)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C423S599000
Reexamination Certificate
active
06764790
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a lithium secondary battery with good charge-discharge cycle characteristics which has low internal resistance, and in particular, to a battery which uses a lithium manganese oxide for a positive active material and is intended for use as a power source for portable electronic devices, electric vehicle motors, hybrid electric vehicle motors, and the like.
BACKGROUND OF THE INVENTION
Reduction in size and weight of portable electronic devices such as portable telephones, camcorders, and lap top computers has proceeded rapidly in recent years. Secondary batteries have come into use for such devices, and use a lithium transition metal compound as a positive active material, a carbon material as a negative material, and an electrolyte which dissolves lithium ion electrolyte in an organic solvent.
Such batteries are generally called lithium secondary (or rechargeable) batteries or lithium ion batteries, and due to their great energy density and the fact the cell voltage is high at around 4 V, they are attracting attention as power sources for electric vehicles (hereinafter referred to as “EV”) and hybrid electric vehicles (hereinafter referred to as “HEV”). With the present concern over environmental problems, these types of vehicles are becoming known to the general public as low pollution vehicles.
The battery capacity and charge-discharge cycle characteristics (hereinafter referred to as “cycle characteristics”) of lithium secondary batteries like these depend largely on the properties of the material used in the positive active material. The lithium transition metal compound uses a positive active material such as lithium cobalt oxide (LiCoO
2
), lithium nickel oxide (LiNiO
2
), and lithium manganese oxide (LiMn
2
O
4
).
Of these, LiMn
2
O
4
is an inexpensive raw material, has high output density, and can handle high voltages. However, its discharge capacity decreases gradually with repeated charging-discharging cycles, and good cycle characteristics are difficult to obtain. However, these disadvantages are being slowly overcome as studies of crystal structure and composition have proceeded in recent years.
Regardless of the type of positive active material used in a lithium secondary battery, reducing the electrical resistance of the positive active material should reduce the internal resistance of the battery. That is, improving the conductivity of the positive active material is the most important matter from the standpoint of improving the characteristics of the battery. Reducing the internal resistance of the battery is very important in order to obtain the large current output necessary for EV's and HEV's to accelerate and climb steep grades, as well as for improving the charging-discharging efficiency.
As one means of solving this problem in the past, fine conductive particles of such materials as acetylene black have been added to the positive active material to improve conductivity and reduce the internal resistance of the battery. However, the addition of acetylene black is a problem in that it reduces the battery capacity by reducing the amount of positive active material that can be used. In addition, since acetylene black is a type of carbon and a semiconductor, it is believed that there are limits as to how much electronic conductivity will improve. Furthermore, acetylene black is voluminous and is difficult to handle in the fabrication of electrode plates. Thus, although adding acetylene black has the advantage of reducing internal resistance, it has the disadvantage of reducing the battery capacity. The proper proportion of acetylene black is known in the prior art due to its ease of manufacture and comparison with other attempted solutions.
SUMMARY OF THE INVENTION
In accordance with the present invention, a lithium secondary battery uses a lithium manganese oxide for a positive active material having a cubic spinel structure which has a crystallite size of 58 nm or greater and/or a lattice distortion of 0.09% or less. The ratio of Li/Mn in the lithium manganese oxide is preferably greater than 0.5.
In accordance with a preferred method for synthesizing the lithium manganese oxide, a mixed compound, including salts and/or oxides of each of the elements, is fired in an oxidizing atmosphere in a range of 650° C. to 1000° C. for 5 to 50 hours. The properties of the resultant crystal are improved by firing two or more times, preferably with an increase in firing temperature over the temperature of the previous firing.
REFERENCES:
patent: 5700597 (1997-12-01), Zhong et al.
patent: 5948565 (1999-09-01), Kelder
patent: 6007947 (1999-12-01), Mayer
patent: 6040089 (2000-03-01), Manev et al.
patent: 6114064 (2000-09-01), Manev et al.
patent: 6117410 (2000-09-01), Ogihara et al.
patent: 6267943 (2001-07-01), Manev et al.
patent: 0 279 235 (1988-08-01), None
patent: 0 728 701 (1996-08-01), None
patent: 2 776 649 (1999-10-01), None
patent: 08-222219 (1996-08-01), None
patent: 10-021910 (1998-01-01), None
patent: 10-182159 (1998-07-01), None
patent: 10-245230 (1998-09-01), None
patent: 10-321227 (1998-12-01), None
patent: 11-302020 (1999-11-01), None
patent: 97/20773 (1997-06-01), None
Thackeray, et al., Lithium Insertion into Manganese Spinels, Mat. Res. Bull., vol. 18, pp. 461-472, Apr., 1983.
Bos Steven
Burr & Brown
NGK Insulators Ltd.
LandOfFree
Lithium secondary battery does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lithium secondary battery, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lithium secondary battery will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3221012