Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-03-22
2001-10-30
Griffin, Steven P. (Department: 1754)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S212000, C429S214000, C429S232000, C429S126000
Reexamination Certificate
active
06309777
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a re-chargeable secondary battery, and more particularly to a explosion-resistant re-chargeable secondary battery having an improved positive electrode structure.
In Japanese laid-open patent publication No. 5-74436, a winding-structured lithium ion secondary battery is disclosed, wherein positive and negative electrodes comprise metal foils coated with an active material and provided with metal tabs connected to electrode terminals and the positive and negative electrodes are separated by a separator which has a property of shut down to a short circuit current.
In Japanese utility model application No. 61-71369, a battery is disclosed, wherein a sharp end portion of a porous core body is covered with a polyethylene tetrafluoride film or a polyester based resin film or a glass fiber film in order to prevent the sharp end portion of the porous core body from penetrating through a separator.
In Japanese utility model application No. 61-180902, a battery is disclosed, wherein a sharp end portion of a porous core body is covered with a fluorine resin film or a glass fiber film in order to prevent the sharp end portion of the porous core body from penetrating through a separator.
In Japanese utility model application No. 60-88225, a battery is disclosed, wherein a sharp end portion of a punched metal body is covered with a fluorine resin film or a glass fiber film in order to prevent the sharp end portion of the punched metal body from penetrating through a separator.
In Japanese laid-open patent publication No. 9-298054, a lithium ion secondary battery is disclosed, wherein an active material coating a positive electrode comprises a lithium manganate having a spinel structure.
The above prior arts are directed to prevent the electrode from penetrating through the separator and from contacting the opposite electrode to form a short circuit.
The above conventional lithium ion secondary battery has sufficient safety under normal states. However, if the above conventional lithium ion secondary battery is over-charged and has a current discharge between the positive and negative electrode through the separator, a temperature of the porous separator is increased and softened and melted, whereby the pores of the porous separator are closed to suppress ions from transferring through the porous-closed separator. As a result, the current between the positive and negative electrodes is reduced whereby the temperature is not increased up to the critical temperature which may case ignition of the battery Namely, the current is shut down.
In recent years, however, the lithium ion secondary battery has been developed in capacity for applicability to a large current usage condition. As the capacity of the battery is increased, the heat generation amount and the heat generation rate are increased so that the temperature of the battery is rapidly increased which causes the separator to completely melt to form a hole in the separator without causing the separator to exhibit a fuse function to close the pores of the separator due to slight melting of the separator. The formation of the hole in the separator allows the discharge current between the positive and negative electrode, whereby a further rapid temperature increase is caused, whereby an ignition or an explosion may appear. So long as it is required for advanced lithium ion secondary battery to increase their capacity as much as possible, the above problems with rapid increase in temperature of the battery are remarkable and serious to the advanced lithium ion secondary battery.
In the above circumstances, it had been required to develop a novel large capacitive secondary battery having sufficient safety not only in normal states but also in abnormal states such as over-charged states.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel battery free from the above problems.
It is a further object of the present invention to provide a novel large capacitive secondary battery having a sufficient safety not only in the normal states but also in abnormal states such as over-charged states.
It is a still further object of the present invention to provide a novel positive electrode structure of a large capacitive secondary battery having sufficient safety not only in normal states but also in abnormal states such as over-charged states.
In accordance with the present invention, an active material free part of a positive electrode is coated with an over-coat material, wherein the over-coat material has at least one of the following properties: suppression of heat transfer from the second part of the electrode to the separator; reduction of a heat transfer rate from the second part of the electrode to the separator; prevention of transfer of excess heat from the second part of the electrode to the separator; electrical isolation of the second part of the electrode from the separator; prevention of charges generated in the first active material from becoming concentrated in the second part of the electrode and discharged from the second part; and prevention of the separator from being melted by a current discharge from or into the second part of the electrode through the separator until the current discharge is shut down by a fuse function of the separator.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.
REFERENCES:
patent: 5326656 (1994-07-01), Meadows et al.
patent: 5821012 (1998-10-01), McCullough
patent: 5998051 (1999-12-01), Poirier et al.
patent: 6001139 (1999-12-01), Asanuma et al.
patent: 6051341 (2000-04-01), Terasaki
patent: 6077623 (1998-06-01), Grosvenor et al.
patent: 6114059 (2000-09-01), Watanabe et al.
patent: 61-204360 (1986-12-01), None
patent: 62-88369 (1987-06-01), None
patent: 62-183365 (1987-11-01), None
patent: 5-74436 (1993-03-01), None
patent: 9-298054 (1997-11-01), None
Ohta Tomoyuki
Satoh Hajime
Shirakata Masato
Griffin Steven P.
NEC Corporation
Strickland Jonas N.
Young & Thompson
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