Electricity: battery or capacitor charging or discharging – Battery or cell charging – Gas controlled
Reexamination Certificate
2000-09-14
2001-05-01
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
Gas controlled
C429S053000
Reexamination Certificate
active
06225785
ABSTRACT:
FIELD OF THE INVENTION
The invention relates in general to safe use of lithium batteries, and more particularly to the testing of lithium battery vents.
BACKGROUND OF THE INVENTION
Lithium batteries, or batteries that contain metallic lithium, a lithium alloy, or a lithium ion, have relatively high energy and are used in many electrical devices. In many military and industrial applications, large and relatively high voltage rechargeable lithium batteries or cells are used. Many of these applications are critical. Therefore, the safety and operation of the lithium batteries is of vital importance. It is often desirable to test the battery design for overall performance and safety. One of the performance criteria is the ability of the battery or cell to release internal pressure without any violent venting. Generally, lithium batteries must be vented as a result of gases or pressure being formed due to the electrochemical reactions under certain load conditions and during charging. Testing procedures, such as Underwriter Laboratory Standards UL 1642, relating to the standard for safety for lithium batteries and abnormal charging tests have proven to be inadequate for many lithium batteries. Underwriter Laboratory standards call for subjecting the cell or battery to a 12-volt DC power supply, charging and overcharging the battery at a current rate three times the vendor's specification for a duration specified by the following formula:
Charging duration or time=(2.5×
C
)/(3×
I
)
Where,
C is the rated capacity of the cell, and
I is the batteries specified charging current.
The Underwiter Laboratory standards test methods are not sufficient to cause many rechargeable lithium batteries or cells to vent. Accordingly, these batteries would be determined safe according to the prior standards, when they may not be. Therefore, there is a need for a new testing procedure that will more adequately test the lithium battery or cell to ascertain the safety of the lithium battery or cell. Ascertaining the safety of the lithium battery or cell design is critical in view of the military and specialized industrial applications to which the lithium batteries or cells are placed. Any failure of a lithium battery, in addition to the failure of operation, may also result in a risk of fire or explosion of the lithium battery or cell. Therefore, it is critical that the lithium battery or cell be adequately tested, particularly the vent, and deemed safe prior to deployment or use. Accordingly, there is a need for an apparatus and test method to assure the safety of lithium batteries or cells.
SUMMARY OF THE INVENTION
The present invention comprises a method and apparatus for evaluating vent design and performance of lithium batteries or cells. A lithium battery or cell having a vent to be tested is subjected to a constant current at a charging rate until the cell or battery capacity reaches 270% of the battery or cell's rated capacity, or until the cell or battery vents, or at three times the battery's specified charging current for a specified predetermined minimum duration. The specified predetermined minimum duration is a function of the rated capacity of the cell and the battery or cell's specified charging current.
Accordingly, it is an object of the present invention to provide a safe lithium battery or cell.
It is a further object of the present invention to test or evaluate vent performance of a lithium battery or cell.
It is an advantage of the present invention that it is suitable for most lithium batteries or cells.
It is a further advantage of the present invention that it is relatively easy to set up and perform.
It is a feature of the present invention that a charging current is applied to the lithium battery or cell until the battery or cell capacity reaches 270% of the minimum rated capacity or until the cell vents.
It is another feature of the present invention that a charging current three times the battery or cell's specified charging current is applied for a minimum specified predetermined time or duration according to a formula.
These and other objects, advantages, and features will become readily apparent in view of the following detailed description.
REFERENCES:
patent: 5895731 (1999-04-01), Clingempeel
patent: 5916704 (1999-06-01), Lewin et al.
patent: 6074775 (2000-06-01), Gartstein et al.
patent: 6163131 (2000-12-01), Gartstein et al.
Au George Wing
Leung Fee Chan
Tereschuk George B.
The United States of America as represented by the Secretary of
Tibbits Pia
Wong Peter S.
Zelenka Michael
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