Electricity: battery or capacitor charging or discharging – Cell or battery charger structure – Charger inductively coupled to cell or battery
Reexamination Certificate
2001-12-21
2003-07-01
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Cell or battery charger structure
Charger inductively coupled to cell or battery
C320S119000
Reexamination Certificate
active
06586909
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a device and method for charging electrochemical cells of a multi-cell battery or the simultaneous charging of multiple batteries. In particular, the invention relates to charging a battery with multiple cells wherein each cell includes a third or charging electrode that is used exclusively for charging. Each cell of the battery is charged simultaneously by coupling a third electrode and a bifunctional electrode in parallel with the battery charger. An induction coil distributes and isolates the charging energy to each cell. The cells of the battery, typically wired in series, require no disassembly for charging. The battery charger is be used with a metal-air battery to prolong the life of the cathode but may also be used to charge common two-electrode multi-cell batteries in parallel without breaking the inter-cell connections. It may also be used to charge a plurality of conventional two-terminal batteries wired in parallel.
BACKGROUND OF THE INVENTION
Generally, battery packs include several battery cells connected in series. Ideally, each of the battery cells within a battery pack will have similar charging, discharging, and efficiency characteristics. However, this ideal scenario is not normally encountered. Thus, a battery pack ordinarily contains several multiple battery cells with each battery cell having different charging characteristics. This condition may produce many problems related to the overcharging and undercharging of the battery cells. For instance, fully charging one battery cell in a battery pack and continuing to charge it may result in overcharging and damage to the fully charged cell. Likewise, ending a charge cycle when only one battery cell is fully charged may result in undercharging one or more of the other battery cells in the battery pack. Therefore, there is a need for a system to provide an isolated charging cycle that accommodates multiple battery cells having varying charging characteristics.
The present invention relates generally to a method and apparatus for rapidly and safely charging a plurality of battery cells from a single power supply. Given the anticipated proliferation of electric vehicles including electric scooters, it will be necessary to have a reasonably standardized recharging apparatus located at, for instance, the vehicle operator's residence, place of business, parking garage, recharge station, and the like. Additionally, the same design may be used to simultaneously charge multiple batteries for portable devices such as personal computers, cellular phones, and the like.
Generally, there are two types of battery cells. Cells that are useful for only a single discharge cycle are called primary cells, and cells that are rechargeable and useful for multiple discharge cycles are called secondary cells. There are many varieties of secondary cells including the common lead-acid and nickel-cadmium (ni-cad) batteries and the less common metal-air batteries such as the zinc-air battery disclosed in patent application Ser. No. 09/552,870, herein incorporated by reference.
Battery packs comprised of metal-air cells provide a relatively light-weight power supply. Metal-air cells utilize oxygen from ambient air as a reactant in an electrochemical reaction. Metal-air cells include an air permeable electrode as the cathode and a metallic anode surrounded by an aqueous electrolyte and function through the reduction of oxygen from the ambient air which reacts with the metal to generate an electric current. For example, in a zinc-air cell, the anode contains zinc, and during operation, oxygen from the ambient air along with water and electrons present in the cell are converted at the cathode to hydroxyl ions. Conversely, at the anode zinc atoms and hydroxyl ions are converted to zinc oxide and water, which releases the electrons used at the cathode portion of the cell. Thus, the cathode and anode act in concert to generate electrical energy.
Metal-air batteries may be charged mechanically and electrically. Mechanical charging is accomplished by physically replacing the electrolyte, the electrodes, or a combination thereof. (For example, see U.S. Pat. Nos. 5,569,555; 5,418,080; 5,360,680; and 5,554,918). Such a charging method requires special equipment, special skills, an inventory of electrolyte and electrodes, and a plan for storing and disposing of hazardous chemicals. Conversely, electrical recharging avoids these disadvantages. The electrically rechargeable metal-air cell is recharged by applying a charging voltage between the anode and cathode of the cell and reversing the electrochemical reaction. During recharging, the cell discharges oxygen to the atmosphere through a vent.
While clean and efficient, electrical charging of a conventional multi-cell battery does have some other disadvantages. In particular, most multi-cell batteries are designed such that the cells are connected in “series” such that the discharge voltage between the battery terminals may be increased. For example, a 12-volt battery is normally comprised of 6 battery cells, each producing 2 volts, wired end-to-end in “series” to provide 12 volts across the two battery terminals. Such a configuration may be electrically recharged by applying a charging voltage across the two battery terminals to reverse the electrochemical process that occurs on discharge. When connected for charging in this fashion, each battery cell wired in series, necessarily receives the identical current flow regardless of its current state of charge and ability to convert this energy to electrochemical storage.
By forcing the same charging current to each cell, charging the battery cells in series is disadvantageous. During the electrochemical recharge cycle of a battery cell, the cell passes through several stages of charging. It is well known that during charging, a phenomenon known as “gassing” occurs, that is to say, the battery electrolyte dissociates into gaseous components which may emanate as bubbles. It is usually desirable to reduce the battery charging current during “gassing” so as to avoid damage to the electrode which would otherwise be caused by maintaining the charging current at the higher levels permissible in the “pre-gassing” or “bulk-charge” phase of charging. Thus, it is desired that the battery charger provide a separate charging circuit to each battery cell such that the charging current may by optimized for each stage of a cell's charging cycle.
It remains that the two-electrode cells of conventional batteries, connected in “series,” cannot be charged “conventionally” through separate charging circuits as the cells are linked end-to-end. Such batteries may charged in parallel by a conventional battery charger only if the inter-cell connections or links are broken or disconnected. In this manner, each cell is independent and separate charging circuits may be attached to each cell.
In the metal-air battery arena, there are two main types of electrically rechargeable batteries. One type includes those with three electrodes for each cell, namely, a bifunctional anode, a discharge cathode, and a charging-electrode (i.e. a third electrode). The discharge cathode is designed to optimize the discharge cycle of the metal-air cell and may be incapable of recharging the cell. Instead, the charging-electrode is used to recharge the metal-air cell. Another type of metal-air cell includes two electrodes, both electrodes being bifunctional. The bifunctional electrodes function in both the discharge mode and the charge mode of the cell, thus eliminating the need for a third electrode. Bifunctional electrodes, however, suffer from a major drawback; they do not last long because the charging cycle deteriorates the discharge system (i.e., bifunctional electrodes suffer from decreasing performance as the number of discharge/charge cycles increase). In some cases as the voltage creeps up the cell may develop a short circuit as a result of a zinc dendrite forming a metallic bridge to the positive electrode, and wi
Renner , Otto, Boisselle & Sklar, LLP
Tso Edward H.
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