Electricity: battery or capacitor charging or discharging – Cell or battery charger structure – For battery pack
Reexamination Certificate
2000-02-18
2001-01-16
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Cell or battery charger structure
For battery pack
Reexamination Certificate
active
06175213
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to batteries, more particularly to a safety device for a thin lithium-ion battery.
BACKGROUND OF THE INVENTION
Improvements in micro-electronics have increased the demand for electrolytic cells in batteries that can be directly incorporated into electronic devices so as to produce a portable finished package, such as for example a cellular phone or a lap top computer. As improvements in micro-electronics reduce the size of the electronic device, the space allotted to a power supply within such device has likewise decreased. It is therefore important to maximize the power per unit space that a battery cell can provide.
When extremely thin or unusually shaped batteries are required, cells contained within flexible packaging have found advantages application. A cell contained within a flexible laminate package provides more efficient use of the space available within a device, in that the cell and package can assume a variety of shapes allowing the battery design to accommodate the space restrictions within the device.
A problem with cells contained within flexible packaging is that they are sensitive to temperature and over-voltage or over-current conditions. In this respect, cells within flexible packages tend to “gas-up” or “swell-up” under extreme temperatures or under extreme over-voltage or over-current conditions. Excessive heat, current or voltage can cause the liquid electrolyte within the cell to decompose into a combustible gaseous by-product. Internal pressures created by this buildup of gas may cause the flexible packaging to swell and even rupture. Still further, without a liquid electrolyte within the cell, the electrodes become resistive elements and energy provided thereto (for example by a battery charger) is converted to heat. If the electrode temperatures exceed the flash point of the hydrocarbon gases generated within the cell, the flexible packaging may rupture. While flexible packaging is less susceptible to a violent venting or catastrophic failure as compared to rigid metal or plastic containers, ruptures of the flexible packaging can damage electronic equipment in the vicinity of the cell.
The present invention overcomes this and other problems and provides a lithium ion battery having a current interrupt safety feature to prevent catastrophic failure with flexible packaging.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there is provided a battery comprised of a rigid, plastic housing defining a generally rectangular cavity. The housing has an intentionally flat surface and a plurality of openings extending from the cavity through the housing. A rechargeable electric cell having a flexible outer package is contained within the cavity of the housing. The cell is generally rectangular in shape and has a flat outer surface and two leads. The leads extend from the cell through select ones of the plurality of openings through the housing. The cell has a normal configuration when experiencing normal operating conditions and an abnormal configuration when experiencing abnormal operating conditions. A flat planar switch is disposed between the flat interior surface of the housing and the flat outer surface of the cell. The switch has at least one switch lead extending therefrom through another of the plurality of openings through the housing. The switch has a first electrical condition when the cell has a normal configuration and a second electrical condition when the cell has an abnormal configuration.
In accordance with another aspect of the present invention, there is provided a battery pack comprised of a rigid housing, and a rechargeable electric cell contained within the housing. The cell has a flexible outer packaging that maintains a normal configuration when experiencing normal operating conditions and an abnormal configuration when experiencing abnormal operating conditions. The cell has a negative lead and a positive lead that are electrically connected to external contacts on the housing. The contacts are adapted to engage contacts on a load or an electrical charging device. An electrical circuit within the housing is connected across the positive lead and the negative lead. The circuit includes a switch element disposed between an interior surface of the housing and an external surface of the cell. The switch element has a normally open switch position when the cell is in the normal configuration and a closed switch position when the cell is in the abnormal condition. The circuit also includes a breaking device having a first closed position connecting the positive lead to a respective one of the external contacts when the switch element is in the normally open switch position, and a second open position breaking the electrical connection between the positive lead and the respective one of the external contacts when the switch element is in the closed switch position.
It is an object of the present invention to provide a rechargeable battery pack for use in an electronic device that includes a safety device to protect the battery from abnormal operation due to a fault condition.
Another object of the present invention is to provide a rechargeable battery pack as described above that is comprised of a housing containing an electrical cell having a flexible outer package and a switch mechanism operable to sense abnormal operating conditions.
Another object of the present invention is to provide a rechargeable battery pack as described above wherein the cell is contained within a flexible outer package and the switch mechanism is disposed within the housing between the cell and the housing.
A still further object of the present invention is to provide a rechargeable battery pack as defined above including electrical circuitry to prevent the cell from experiencing abnormal operating conditions and to prevent damage to circuits and components external to the battery pack.
These and other objects and advantages will become apparent from the following description of a preferred embodiment of the invention, taken together with the accompanying drawings.
REFERENCES:
patent: 5656355 (1997-08-01), Cohen
Centa John A.
Shokoohi Frough K.
Kusner Mark
NTK Powerdex, Inc.
Tibbits Pia
Wong Peter S.
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