Patent Application
20080235944
1. Field
The disclosed apparatuses and article of manufacture relates generally to energy storage devices, and particularly to effectively reducing an overall size of such an energy storage device.
2. Related Art
Electrodes are widely used in many devices that store electrical energy, including primary (non-rechargeable) battery cells, secondary (rechargeable) battery cells, fuel cells, and capacitors. Important characteristics of electrical energy storage devices include energy density, power density, maximum charging rate, internal leakage current, equivalent series resistance (ESR), and durability, i.e., the ability to withstand multiple charge-discharge cycles. For a number of reasons, double layer capacitors, also known as supercapacitors and ultracapacitors, are gaining popularity in many energy storage applications. The reasons include availability of double layer capacitors with high power densities (in both charge and discharge modes), and with energy densities approaching those of conventional rechargeable cells.
Double layer capacitors use electrodes immersed in an electrolyte (an electrolytic solution) as their energy storage element. Typically, a porous separator immersed in and impregnated with the electrolyte ensures that the electrodes do not come in contact with each other, preventing electronic current flow directly between the electrodes. At the same time, the porous separator allows ionic currents to flow between the electrodes in both directions. As discussed below, double layers of charges are formed at the interfaces between the solid electrodes and the electrolyte. Double layer capacitors owe their descriptive name to these layers.
When electric potential is applied between a pair of electrodes of a double layer capacitor, ions that exist within the electrolyte are attracted to the surfaces of the oppositely-charged electrodes, and migrate towards the electrodes. A layer of oppositely-charged ions is thus created and maintained near each electrode surface. Electrical energy is stored in the charge separation layers between these ionic layers and the charge layers of the corresponding electrode surfaces. In fact, the charge separation layers behave essentially as electrostatic capacitors. Electrostatic energy can also be stored in the double layer capacitors through orientation and alignment of molecules of the electrolytic solution under influence of the electric field induced by the potential.
In comparison to conventional capacitors, double layer capacitors have high capacitance in relation to their volume and weight. There are two main reasons for these volumetric and weight efficiencies. First, the charge separation layers are very narrow. Their widths are typically on the order of nanometers. Second, the electrodes can be made from a porous material, having very large effective surface area per unit volume. Because capacitance is directly proportional to the electrode area and inversely proportional to the widths of the charge separation layers, the combined effects of the large effective surface area and narrow charge separation layers result in capacitance that is very high in comparison to that of conventional capacitors of similar size and weight. High capacitance of double layer capacitors allows the capacitors to receive, store, and release large amounts of electrical energy.
Achieving higher energy densities, for storage of greater amounts of energy, and decreasing cell size, to improve portability are two parameters which drive energy storage device design today. Many modern energy storage device electrode cores employ a “jelly-roll” technique for circumferentially winding a relatively planar electrode core about a longitudinal axis in order to increase energy storage surface area.
One design issue with energy storage devices is energy storage capacity scalability with reduction in overall cell size. When manufacturing energy storage device cells smaller than “C-cell” size, cost effectiveness becomes a problem, because as the overall cell size is decreased, the ratio of active material to total material trends to zero. That is, as the overall cell size of an energy storage device is scaled down, a ratio of active materials verses total materials of the device tends toward zero. There is a necessary “overhead” of inactive materials needed for the device, such as terminations, current collectors, and packaging that does not scale proportionally with overall cell size reduction. Active materials, on the other hand, do scale proportionally with a reduction in overall cell size.
Therefore, a need exists to improve cost effectiveness in energy storage device cells smaller than “C-cell” size. The present teachings provide solutions for the aforementioned issues.
Embodiments of the disclosed method and apparatus will be more readily understood by reference to the following figures, in which like reference numbers and designations indicate like elements.
The presently disclosure teaches of a corrugated electrode core terminal interface apparatus and method for making the same, which provides a cost-effective means for reducing an overall size of an energy storage device, such as for example an ultracapacitor or a battery, when such devices are scaled below “C-cell” size. In one embodiment, such cost effectiveness with scaling is made possible, because the present teachings eliminate the prior art need for excess foil overhang in an electrode element, which the prior art has used to crimp or weld the electrode element to a terminal.
In one embodiment, the current collector foil members 102 and 106 further comprise an activated element, such as for example carbon. The reader is directed to U.S. Pat. Nos. 6,451,073, 6,059,847, 7,102,877 for general background on the use of activated carbon on a current collector foil.
In one embodiment, there is no “overhang” with respect to either the first current collector foil member 102, the separator element 104, or the second current collector foil member 106. That is, lateral and lengthwise dimensions of the first current collector foil member 102, the separator element 104, and the second current collector foil member 106 are approximately identical. In prior art solutions, a collector foil(s) had a “wider” lateral dimension than a separator, thereby creating an “overhang”. The extra lateral portion(s) of the “wider” collector foil(s) have been attached to a terminal or collector by an affixing means, such as for example welding by creating the “overhang” of the current collector foil(s) to a terminal or current collector. The “overhang” reduces cost-effectiveness of an energy storage device cell, as will be appreciated by those of ordinary skill in the art. The present disclosure is useful to eliminate such an overhang, thereby improving the cost effectiveness of scaling an energy storage device, such as for example an ultracapacitor or lithium ion battery, to below C-cell sizes. Moreover, the preset teachings circumvent the need for a fixed portion of inactive material by integrating in the plurality of termination wires to current collector foils. The aforementioned eliminates the need for excess foil overhand for which the prior art has relied upon to crimp or weld thereto for conduction between the electrode and the terminal.
The prior art has employed “jelly roll” electrode architectures for electrode construction. The present teachings change, by contrast break the jelly roll paradigm by using a corrugated style of electrode assembly pair for packing into a cell package, such as for example a prismatic cell package.
In one embodiment, the plurality of termination wires 108 are positioned at fold seams of the current collector foils 102 and/or 106 as shown in
Prior art solutions, implementing the “jelly roll” manufacturing process scales to large cells better than sub-C cells. The present teachings help eliminate the need for direct foil to can and lid welding which require considerable axially length in the package to accommodate.
As illustrated in
According to the present teachings, the entire corrugated electrode surface along the electrode width (W) is active. In some embodiment, there still may be some separator element 104 overhang.
The present teachings provide a high pulse power capability for sub-C cells, and also facilitates improved power cell ratings. The present teachings are adaptable for low capacity, but high pulse power applications such as automotive power net stabilization and high power load distributed module use.
The foregoing description illustrates exemplary implementations, and novel features, of aspects of an method of making for effectively providing an energy storage electrode core. Given the wide scope of potential applications, and the flexibility inherent in electro-mechanical design, it is impractical to list all alternative implementations of the method and apparatus. Therefore, the scope of the presented disclosure should be determined only by reference to the appended claims, and is not limited by features illustrated or described herein except insofar as such limitation is recited in an appended claim.
While the above description has pointed out novel features of the present teachings as applied to various embodiments, the skilled person will understand that various omissions, substitutions, permutations, and changes in the form and details of the methods and apparatus illustrated may be made without departing from the scope of the disclosure. These and other variations constitute embodiments of the described methods and apparatus.
Each practical and novel combination of the elements and alternatives described hereinabove, and each practical combination of equivalents to such elements, is contemplated as an embodiment of the present disclosure. Because many more element combinations are contemplated as embodiments of the disclosure than can reasonably be explicitly enumerated herein, the scope of the disclosure is properly defined by the appended claims rather than by the foregoing description. All variations coming within the meaning and range of equivalency of the various claim elements are embraced within the scope of the corresponding claim. Each claim set forth below is intended to encompass any system or method that differs only insubstantially from the literal language of such claim, as long as such apparatus or method is not, in fact, an embodiment of the prior art. To this end, each described element in each claim should be construed as broadly as possible, and moreover should be understood to encompass any equivalent to such element insofar as possible without also encompassing the prior art.
