Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Reexamination Certificate
2000-02-17
2001-09-18
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
C320S116000
Reexamination Certificate
active
06291972
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of lithium batteries, and more particularly, to a system for the formation, charging, discharging, and equalization of lithium batteries.
BACKGROUND OF THE INVENTION
Rechargeable, secondary batteries such as lithium-polymer batteries, show great promise in providing power sources for a variety of applications such as portable electronic devices. Such batteries may be formed as a thin, somewhat rectangular form factor with large available power density. Once the battery is formed, it is then subjected to a formation or charging process.
Battery formation is the process in which secondary cells are energized to effectuate their capability to deliver electrical energy. Secondary cells and batteries are assembled with electronically inert chemical compounds. In order to energize the devices by converting the inert substances into electroactive species and to prepare them for service, one must provide an initial, slow charge called formation or forming. This process is normally executed in a two-phase process. First, a constant current is applied to the cell or battery up to a predetermined voltage limit. At that point, the voltage applied to the battery terminals is maintained at a constant value and the current trails off to a low value. Formation can then be terminated based upon a total number of ampere-hours input into the cell or group of cells or a current limit as the charging current decreases with the internal resistance of the cell.
While this procedure is implemented routinely for a wide range of battery chemistries, there are a number of associated shortcomings, particularly with cells based upon lithium chemistry. The first shortcoming relates to the overall system for connecting the cells to the charge apparatus for the formation process. Commonly, the cells being formed or charged are connected in series to one another as part of a single regulated circuit. In this configuration there can be no provision for treating a potentially weak cell without affecting, perhaps adversely, other cells in the circuit. Moreover, for large batches of cells, such as more than 100 cells or batteries, the voltage requirements may become extreme, and the power supply specifications prohibitively expensive and dangerous.
The second shortcoming of the standard formation process and instrumentation is the means of electrically and mechanically coupling a battery or cell to the formation circuit. Most lithium cells, especially lithium-polymer cells, are manufactured in custom form factors without standardized, rigidly defined dimensions, particularly in length and width. Also, the electrical contacts or terminals of the cells are generally flexible metallic foil tabs which are difficult to localize. That means that interfacing these cells with the formation circuit poses a particular challenge. Clamps can be used, but labor becomes intensive as the number of cells to be formed increases for a particular batch of cells. Connection through probes oriented normal to the plane of the terminal tabs is less laborious, but stabilizing the flexible strips becomes critical.
Thus, there remains a need for a lithium battery formation system in which large batches of cells or batteries may be formed and charged safely and effectively and in which the cells in the batch are more uniformly charged in the process. There is a further need for a system for safely and effectively connecting lithium batteries into the formation and charging system. The system should make the coupling of the cells into the system easy and thus eliminate the difficulties in the art of interfacing the cells, should makes registration of the cells in the system easy to accomplish, and should eliminate the need to stabilize the flexible strips of the battery cells.
SUMMARY OF THE INVENTION
The present invention addresses these and other shortcomings in the art with an improved system for the formation of secondary batteries, such as lithium ion and lithium-polymer cells. The first aspect of the present invention provides for equalization of each of a number of the aforementioned cells connected in series. Each independent circuit supplements the bulk formation charge of 1 to 5 Amperes with a small equalization current (&mgr;A to mA) to normalize the terminal Voltage and, hence, the conditions of all cells. No complex external circuitry is required, as a small power supply for each cell position will suffice. The control circuit is simplified further by the generation of a single Voltage profile applied only to the first cell in the string or to the whole string. The term “voltage profile” refers to the voltage as viewed over time. This new method of control is called “polarization control” and eliminates the need for a separate current regulator for each cell and is universal for cells of any size of a specific chemistry. The profile is simply repeated for every cell in the series and ensures that every position is voltage-equalized. Furthermore, as the embodiment of the equalizer connected to each cell is a bipolar potentiostat, the benefit can be realized during discharge as well as charging processes.
In a second aspect of the present invention, the embodiment is extended to include a parallel aggregate of cells connected in series, and this arrangement eliminates the need for current regulation for each cell. Each parallel-grouped cell is equipped with a current-limiting device that protects the entire system against excessive current drains from a particularly weak cell. This arrangement, referred to herein as constant average current, provides a mechanism for self-equalization of the cells configured in this way.
As in the embodiment consisting of purely series-arranged cells, in this system cells in parallel are governed by the same voltage profile, and each cell draws current from a Voltage-regulating power supply according to its state of health. In some cases, cells will even be discharging slight currents to the bipolar power supply. However, since the power supply is a bipolar potentiostat, only one assemblage of electrical connections is needed for each cell. For large populations of cells the net equalization current is zero.
By means of extension of the concepts enumerated above, one can envision the embodiment of the innovation as a charging instrument. Cells may be charged optimally individually or in strings, as described above. The same equalizer circuitry and polarization control methodology as with the formation system may be applied.
In yet another aspect of this invention, a means is provided for connecting cells to the electronic instrument containing the voltage-regulating power supply. While most formation systems require large trays with imbedded circuitry for interfacing with the test/inspection instrument, the present invention provides a cell holder capable of providing safe, secure electrical connection of individual flat lithium ion and lithium-polymer cells directly to the formation channels without cables or unwieldy trays and pallets. Further, these special holders provide for reliable termination at the terminal tabs.
These and other features of this invention will be apparent to those skilled in the art from a review of the detailed description along with the accompanying drawings.
REFERENCES:
patent: 5631101 (2000-05-01), Amero, Jr.
patent: 6020717 (2000-02-01), Kadouchi et al.
patent: 6078165 (2000-06-01), Ashtiani et al.
patent: 6099986 (2000-08-01), Gauthier et al.
Bracewell & Patterson LLP
Luk Lawrence
Wong Peter S.
LandOfFree
System for battery formation, charging, discharging, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System for battery formation, charging, discharging, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System for battery formation, charging, discharging, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2498704