Abstract:
An energy-storage device electrode core is disclosed that features relatively low-inductive impedance (and thus low equivalent series resistance (ESR)). Also disclosed is an energy-storage device electrode core that features a radii-modulated electrode core that forms extra vias to facilitate efficient heat removal away from the electrode, thus improving the performance and capabilities of an energy-storage device so equipped. The internal electrode core heat-removal vias are defined by the modulation patterns that in turn define the size and layout of the folds in the electrode, which are circumferentially collapsed about the center axis of the electrode core.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of and is a continuation-in-part of U.S. patent application Ser. No. 11/536,916, which was filed on Sep. 29, 2006, and which is hereby incorporated by reference for all purposes. This patent application also claims the benefit of and is a continuation-in-part of U.S. patent application Ser. No. 11/536,980, which was filed on Sep. 29, 2006, and which is hereby incorporated by reference for all purposes. Finally, this patent application also claims the benefit of and is a continuation-in-part of U.S. patent application Ser. No. 11/537,487, which was filed on Sep. 29, 2006, and which is hereby incorporated by reference for all purposes. 
     
    
     BACKGROUND 
       [0002]    The disclosures contained herein relate generally to energy-storage devices and in particular relate to increasing energy-storage device electrode core operational performance characteristics. 
         [0003]    Energy-storage device element design is driven by a variety of parameters, such as, for example, thermal characteristics and electromagnetic problems (e.g., equivalent series resistance (ESR), inductance). One of the most important elements of an energy storage device for optimal functioning is an electrode core. Key operational performance characteristics for the electrode core of an energy-storage device (e.g., ultracapacitor, battery, hybrid energy-storage device, etc.) include, inter alia, thermal control and inductance effects. 
         [0004]    A need exists to increase thermal performance of energy-storage device elements, particularly within the electrode core. Also, design enhancements are needed in the area of thermal gradients within the energy-storage device cell and cell-packs (multi-cell modules). Moreover, control of heat flow away from the electrode core is becoming more important, particularly as industry needs, such as electric automobiles, drives the commercial sector. Any advancement in the efficiency of thermal performance will increase the utility of an associated energy storage device. As industry usage of energy-storage cell modules increases (such as, for example, in “hybrid” automobiles), the need to control thermal gradients in such modules is fast becoming evident. In addition, usage of such cell modules in geographical regions which have relatively high ambient temperatures, would greatly, benefit from a better energy-storage device design emphasizing thermal considerations. 
         [0005]    Another design issue with some energy-storage devices, such as modern ultracapacitor cells, is internal inductance, generated by the circumferential current flow about the “jelly-roll” inside the cell core. Such an inductance creates an undesirable impedance for an ultracapacitor electrode core, ultimately degrading performance, as will be appreciated by those of skill in the art. Any reduction in the amount of internal inductance within the electrode core would improve performance. 
         [0006]    Moreover, as will be appreciated by those of ordinary skill in the energy-storage device electrode core arts, inductance of ultracapacitor electrode cores causes damage to cell-module balancers, due to over-voltage. Therefore, a need exists for a reduction in failure of energy-storage device cell modules due to balancer damage. 
         [0007]    Furthermore, modern cell construction techniques for ultracapacitors includes a core involute. The core involute contributes to sharp bend radii of an electrode core (contributing to “hot” spots in the electrode core), and possibly contributes to leakage current. Such hot spots and leakage current further degrade ultracapacitor performance. 
         [0008]    Therefore, a need exists to improve the thermal and electromagnetic performance of an energy storage device electrode core, as well as reducing problematic effects of a core involute. 
       BRIEF SUMMARY 
       [0009]    An energy-storage device electrode core is disclosed that features relatively low-inductive impedance (and thus low equivalent series resistance (ESR)) as compared to the prior art. The disclosed energy-storage device electrode core departs from a traditional “jelly-roll” type of core by effectively reducing the number of “turns” in the electrode core (and thus reducing the inductive impedance of the electrode core) to approximately one, yet maintaining a comparable effective electrode surface area. 
         [0010]    Also disclosed is an energy-storage device electrode core that features a radii-modulated electrode core that forms extra vias to facilitate efficient heat removal away from the electrode, thus improving the performance and capabilities of an energy-storage device so equipped as compared to the prior art. The internal electrode core heat-removal vias are defined by the modulation patterns that in turn define the size and layout of the folds in the electrode, which are circumferentially collapsed about the center axis of the electrode core. 
         [0011]    The disclosed advances in the design of an energy-storage device electrode core enhance the overall operating performance of an energy-storage device. 
         [0012]    Nothing within this Brief Summary section is intended to limit the scope of the disclosure contained within this entire patent application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Embodiments of the disclosed apparatuses and methods will be more readily understood by reference to the following figures, in which like reference numbers and designations indicate like element. The figures are exemplary only and are not intended to limit the scope of the disclosures discussed herein. 
           [0014]      FIG. 1   a  illustrates a front-plan view of a current-collector foil having a plurality of carbon-electrode elements and a plurality of fold-zone regions defined between a plurality of demarcation regions, according to one embodiment of the present teachings. 
           [0015]      FIG. 1   b  illustrates a front-plan view of a separator element, according to one embodiment of the present teachings. 
           [0016]      FIG. 2  illustrates a perspective view of an electrode-core element, according to one embodiment of the present disclosure. 
           [0017]      FIG. 3  illustrates a perspective view of an electrode core, according to one embodiment of the present teachings. 
           [0018]      FIG. 4  illustrates a perspective view of a localized region of an annular electrode core, according to one embodiment of the present disclosure. 
           [0019]      FIG. 5  illustrates GRAPH 1. 
           [0020]      FIG. 6  illustrates GRAPH 2. 
           [0021]      FIG. 7  illustrates GRAPH 4. 
       
    
    
     DETAILED DESCRIPTION 
     Overview 
       [0022]    The present teachings disclose an apparatus and article of manufacture for optimizing energy-storage electrode core performance. In some embodiments, undesirable inductance is addressed and reduced to enhance electrode core performance. In other embodiments, undesirable thermal heat flow within an electrode core is addressed and reduced to enhance electrode core performance. 
         [0023]    Referring now to  FIGS. 1   a - b , one illustrative exemplary embodiment of an energy-storage electrode  100  is shown. In one embodiment, the energy-storage electrode  100  comprises a heat-flow-controlled ultracapacitor element, comprising a first current-collector foil element  102 , a separator element  162 , and a second current-collector foil element (not shown). In some embodiments of the present teachings, the second current-collector foil element is identical to the first current-collector foil element  102 . In one alternate embodiment of the present disclosure, the energy-storage electrode  100  comprises a variable-radii, annular-electrode core adapted for use in an energy-storage device, comprising a first current-collector foil element  102 , a separator element  162 , and a second current-collector foil element (not shown). In some embodiments of the present teachings, the second current-collector foil element is identical to the first current-collector foil element  102 . In one embodiment, the energy-storage device is an ultracapacitor; however, the present teachings may readily be adapted for use in a lithium-ion battery, hybrid energy-storage devices, or literally any type of energy-storage device which requires an electrode core. In a heat-flow-controlled ultracapacitor embodiment, heat flow is controlled by the ultracapacitor, because the ultracapacitor functions to remove heat from the inside of the ultracapacitor electrode core, as will be described further below. 
         [0024]    In one embodiment, the first current-collector foil element  102  is composed of, inter alia, aluminum.  FIG. 1   a  illustrates how electrode material (such as, for example, carbon), is disposed upon both sides of a double-sided current-collector foil. In one embodiment, carbon electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118  are disposed along a first side of the first current-collector foil element  102 . Also illustrated in  FIG. 1   a  is a modulation of electrode width such that the progressively thinner spans of carbon can be folded back upon itself in the final configuration, as will be described further below. The carbon electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118  follow a pulse-width-modulation type of pattern; however literally any kind of shape modulation pattern of the carbon electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118  is within the scope of the present teachings; for example, amplitude and/or phase modulated patterns. 
         [0025]    In one embodiment, a plurality of carbon-electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118  are disposed upon both sides of the current-collector foil  102 . It will be appreciated that only one side of the double-sided current-collector foil  102  is illustrated in  FIG. 1   a . Moreover, the plurality of carbon-electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118  each have an identical matched pair respectively disposed on another side of the double-sided current-collector foil  102  (not shown). In other words, carbon-electrode elements are disposed in a modulated pattern on both sides of the double-sided current-collector foil  102  in a similar fashion. 
         [0026]    Each of the plurality of carbon-electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118  is bounded by a plurality of fold-zone regions defined between a plurality of fold-zone demarcation regions  120   a ,  120   b ,  120   c ,  120   d ,  120   e ,  120   f ,  120   g ,  120   h , and  120   i , as illustrated in  FIG. 1   a . In other words, a first fold-zone region is defined between fold-zone demarcation regions  120   a  and  120   b , whereas a second fold-zone region is defined between fold-zone demarcation regions  120   b  and  120   c . Additional fold zones are similarly defined. 
         [0027]      FIG. 1   b  illustrates a front-plan view of a separator element  162 , having a front side and a back side. The separator element  162  has dimensions of length and width approximately identical to the first current-collector foil element  102  described above. In the completed assembly of the apparatus, the separator  100  is interposed between the first current-collector foil element  102  and a second current-collector foil element, as will be described further below. The separator  162  functions to prevent the first current-collector foil element  102  from electronically shorting to the second current-collector foil, while simultaneously allowing ionic current to flow therebetween. 
         [0028]      FIG. 2  illustrates one exemplary embodiment of a perspective view of an annular electrode core element  200  adapted for use in an ultracapacitor. The annular electrode-core element  200  generally comprises a first current-collector foil element  204 , a first separator element  206 , a second current-collector foil element  208 , and a second separator element  209 . 
         [0029]    In one exemplary embodiment, the annular electrode core element  200  comprises a radii-modulated, annular electrode core. In this embodiment, the first current collector element  204  of width “W”, the first separator element  206 , the second current collector foil element  208  of width “W”, and the second separator element  209  are layered and folded (collapsed) along the plurality of fold-zone demarcation regions  120   a ,  120   b ,  120   c ,  120   d ,  120   e ,  120   f ,  120   g ,  120   h , and  120   i  as described above with reference to  FIG. 1   a . The two current collector foils  204  and  208  are displaced axially such that one foil side “A” overhangs a separator element while the opposite foil side “B” overhangs the separator diametrically opposed to “A”. 
         [0030]    The annular electrode-core element  200 , when folded along the fold-zone demarcation regions, collapses into a structure having a continuous gradation of fold peaks. The peak amplitude “P”, as shown in  FIG. 2 , of the folds is selected so that the outer folds define an outside radius, and a plurality of intermittently disposed inner peaks define an inside radius of a final electrode-core assembly, as will be described further below. A length of the outside radius corresponds to a relatively large amplitude fold  214 , whereas the inside radius corresponds to a relatively small amplitude fold  210  and/or  212 . In one embodiment, the electrode-core element  200  is adapted for use as a heat-flow-controlled electrode core, wherein the relatively small amplitude folds function to form a thermal via, facilitating heat removal from the electrode core. 
         [0031]    It will be appreciated that the relative amplitude of each fold zone is determined by the width of the plurality of carbon-electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118 , as described above with respect to  FIG. 1   a . In one exemplary embodiment, the small amplitude fold  212  corresponds to the small width of the carbon-electrode element  110  of  FIG. 1   a , whereas the large amplitude fold  214  corresponds to the large width of the carbon electrode element  118  of  FIG. 1   a.    
         [0032]    When folded (collapsed), the plurality of carbon-electrode elements  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 , and  118  are relatively flat in localized regions between the folds, as will be described further below with respect to  FIGS. 3 and 4  in embodiments where an energy-storage device electrode core is formed into an annular electrode core. Because tight foil radii are restricted to only the inner and outer edges of the annular electrode-core element  200 , heat dissipation is maximized. Moreover, the “fan-fold” structure readily leads itself to a hollow-cored structure (as will be described further below in greater detail), in which an inner passage is available for heat removal from an energy-storage device electrode cell core. 
         [0033]      FIG. 3  illustrates a perspective view of an electrode core  300 , according to one embodiment of the present teachings. In one embodiment, the electrode core  300  comprises a plurality of fold peaks  321 ,  322 ,  323 , and  324 , an inner radius (“r a ”)  302 , and an outer radius (“r i ”)  304 . In the illustrative exemplary embodiment of  FIG. 3 , an integral number of peaks (“Np”) (e.g., the plurality of fold peaks  321 ,  322 ,  323 , and  324 ) are oriented about the center of the electrode core  300 , as will be described further below. 
         [0034]    In one embodiment, the annular electrode-core element  200  of  FIG. 2  is compressed (or wrapped) into a circumferentially oriented “accordion-type” shape, in order to achieve the electrode core  300  of  FIG. 3 . In this embodiment, the electrode core  300  is compressed circumferentially so that an integral number of peaks Np is four (i.e., the plurality of fold peaks  321 ,  322 ,  323 , and  324 ). In this configuration of the electrode core  300 , a plurality of densely packed electrode carbon-powder patches (not shown) are kept flat along radial lines of a final assembly of the present teachings. Once compressed circumferentially, the carbon-electrode patches fill the annular region (defined in a region between r a  and r b ) without loss of active volume, because the presently disclosed teachings provide a Pulse-Width-Modulation (“PWM”) pattern with a sufficient number of steps N s  between r a  and r b . 
         [0035]    When assembled, the electrode core  300  permits a different type of conductive pathway for current flow, relative to prior-art methods. In prior-art solutions, the normal pathway for current flow in an energy-storage device has been along a circumferential axis, around the wound electrode core. Such a pathway contributes to inductive impedance (due to such a long current path through the many turns of a jelly-roll type of electrode) and reduces overall performance by increasing the equivalent series resistance (ESR) and reducing the overall efficiency of the energy-storage device. By contrast, in the present disclosure, a significant advancement in these problems is achieved because the many turns of the typical jelly-roll-type of electrode core are eliminated; that is, the electrode has less of a “coil” effect, and thus lower inductive impedance. Moreover, the resultant conductive pathway is a substantially along a longitudinal axis of an energy-storage device, thereby eliminating the circumferential current path. Therefore, the present disclosure provides a significantly shorter current path, less inductive impedance, and greater overall efficiency, increased longevity, and reduced equivalent series resistance for the energy-storage device. 
         [0036]      FIG. 4  illustrates a perspective view of a localized region of an annular electrode core  400 , according to one embodiment of the present disclosure.  FIG. 4  highlights how a plurality of carbon-patch areas (e.g.,  410  and  414 ) accumulate to form pie-shaped zones (“thermal vias”) such that an entire volume of an annular ring is filled. In this embodiment, the active portions of the carbon electrodes completely fill an annular region and the carbon-electrode deposits are approximately flat. In one embodiment, an amount of carbon-particle-binder material required is reduced, because a resulting electrode matrix will not be exposed to physical tension, such as is found in current so-called “jelly-roll” configurations for energy storage devices, particularly at the core involute. 
         [0037]    In one embodiment, the annular electrode core  400  is adapted to improve energy-storage device cell thermal performance, by eliminating the jelly-roll involute. Additionally, this embodiment facilitates approximately complete parallel plate electrode operation, thereby allowing for use of lower tensile strength matrix binders for the carbon powder used for such devices. 
         [0038]    In some embodiments of the present teachings, a sinusoidal-modulation fold pattern is employed for the annular electrode core. To describe these embodiments, each “fold” generally begins at an outer radius r 0  and progressively decreases in radius with each successive fold, until an inner radius r i0  is reached, as will now be described in greater detail. In one embodiment, r 0  is equal to r b , and r i0  is equal to r a , as described above with respect to  FIGS. 3 and 4 . Calculation of the relative radial length changes for each successive fold will now be disclosed. 
         [0039]    In order to determine a relative radii length for each successive fold in an annular electrode core, the famous “golden ratio” is employed. The golden ratio expresses the relationship that the sum of two quantities is to the larger quantity as the larger is to the smaller. The golden ratio is an irrational number as expressed in EQUATION 1. In some embodiments of the present disclosure, the golden ratio is used as a starting point for initial sizing for the radii amplitudes peak-to-peak, as will now be described. 
         [0000]    
       
         
           
             
               
                 
                   
                     Ψ 
                     = 
                     
                       
                         
                           5 
                         
                         - 
                         1 
                       
                       2 
                     
                   
                    
                   
                     
 
                   
                    
                   
                     Ψ 
                     = 
                     0.618 
                   
                 
               
               
                 
                   EQUATION 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0040]    Also, using the golden ratio as a starting point, note that: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         Ψ 
                         r 
                       
                       = 
                       
                         ( 
                         
                           
                             1 
                             Ψ 
                           
                           - 
                           1 
                         
                         ) 
                       
                     
                     ; 
                   
                    
                   
                     
 
                   
                    
                   
                     
                       Ψ 
                       r 
                     
                     = 
                     0.618 
                   
                 
               
               
                 
                   EQUATION 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
         [0041]    Define a number of folds “N” over a half period of radii modulation pattern:
       N=20; K=1 . . . N       
 
         [0043]    Now, in one embodiment:
       r 0 =30 mm; initial outer radius for the other annular package.       
 
         [0045]    Then let the maximum excursion of r i (θ)−0.85 r 0 , which results in: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       r 
                       i0 
                     
                     = 
                     
                       
                         ( 
                         
                           1 
                           - 
                           Ψ 
                         
                         ) 
                       
                       · 
                       
                         
                           r 
                           0 
                         
                         2 
                       
                     
                   
                   ; 
                 
               
               
                 
                   EQUATION 
                    
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
       
         
           
             
               
                 r i0 =5.729 mm; inner radius starting points on magnitude 
                 r pp =0.85r 0 −r i0 ; r pp =19.771 mm peak-to-peak variation. 
               
             
           
         
       
     
         [0048]    In one embodiment, a modulated radii composite function is calculated according to EQUATION 4, and the relative radial lengths are shown in GRAPH 1, illustrated in  FIG. 1 : 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       r 
                       i 
                     
                      
                     
                       ( 
                       k 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           r 
                           pp 
                         
                         2 
                       
                       · 
                       
                         sin 
                          
                         
                           ( 
                           
                             
                               2 
                                
                               
                                 k 
                                 · 
                                 π 
                               
                             
                             N 
                           
                           ) 
                         
                       
                     
                     + 
                     
                       r 
                       i0 
                     
                     + 
                     
                       
                         
                           r 
                           pp 
                         
                         2 
                       
                        
                       
                           
                       
                        
                       mm 
                     
                   
                 
               
               
                 
                   EQUATION 
                    
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
         [0049]    The actual fold pattern length are then r i0 −r i (k). 
         [0000]    Now calculating the actual fold lengths (such as for example to calculate the active carbon-electrode sectional area) would be the function (r i0 −r i (k)), which is plotted in GRAPH 2 shown in  FIG. 6 . 
         [0050]    In one embodiment, an integral number of “cycles” around the annular volume is calculated, such as for example in a 3N pattern, wherein the final pattern is shown by GRAPH 3 in  FIG. 7 . 
         [0051]    In this embodiment, N=60, for three full cycles, with each cycle reflecting 20 folds, as shown above. 
         [0052]    The presently disclosed energy-storage device electrode core embodiments are a significant progression on modem design techniques. The present teachings eliminate the need for a core involute and leave the electrode core hollow for other uses, such as for example evacuation of heat from cell (such as for example using liquid, air, etc. . . . ). Also, in some embodiments the foil edges of the electrode are only present at the inner and outer radii, which means that thermal conduction is enhanced (i.e., no carbon layer intervenes), and heat removal is faster and more efficient. Such thermal benefits of the present teachings contribute to increased energy-storage device cell longevity and overall performance because (1) the cell has more efficient operation, (hence less heat generated), (2) the cell is subjected to more rapid heat removal (that is, more efficient cooling), and (3) the cell can operate at higher temperatures without failure. 
         [0053]    In one embodiment, heat is routed directly to one or more endcaps of an energy-storage device. Such routing facilitates cooling and eliminates and/or reduces thermal gradients inside the energy storage device. Therefore, individual energy cells, and/or cell modules, are capable of being pushed to higher thermal limits than previously proposed solutions. 
         [0054]    Moreover, a substantial reduction in equivalent series resistance (ESR) is achieved by the present disclosure, over prior-art solutions, because the inductance of the electrode core is greatly reduced by eliminating the many turns of a typical jelly-roll type electrode core, and because current largely flows along a longitudinal axis of an energy storage device electrode core, thereby eliminating the previous circumferential current path about the electrode core. The equivalent series resistance (ESR) is reduced as inductive impedance is reduced, due in part to the shortened conductive pathway along which the current must travel within the electrode core. 
       CONCLUSION 
       [0055]    The foregoing description illustrates exemplary implementations, and novel features, of aspects of an apparatus and article of manufacture 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 is not limited by features illustrated or described herein. 
         [0056]    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. 
         [0057]    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. 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.