US20100203384A1

US20100203384A1 - Electrode folds for energy storage devices

Info

Publication number: US20100203384A1
Application number: US12/694,641
Authority: US
Inventors: Jon Kenneth West; Martin Patrick Higgins; Eileen Higgins; Julius Regalado; Anthony George; Xin Zhou; Nelson Citta; Myles Citta; Allen Michael; Kenneth Cherisol; Daniel J. West; Barbara Patterson
Original assignee: G4 Synergetics Inc
Current assignee: G4 Synergetics Inc
Priority date: 2009-01-27
Filing date: 2010-01-27
Publication date: 2010-08-12
Also published as: CN102341935A; JP2016001627A; CA2750164A1; CA2750166A1; KR20110120914A; EP2392039A1; HK1166881A1; JP2012516541A; JP2012516542A; CN105047956A; WO2010087963A1; US20100190047A1; CN102341935B; CN102341949A; WO2010087992A1; EP2392047A1; US20140370374A1; KR20110120903A; CA2750164C; HK1214034A1

Abstract

A stacked energy storage device (ESD) has at least two conductive substrates arranged in a stack. Each cell segment may have a first electrode unit having a first active material electrode, a second electrode unit having a second active material electrode, and an electrolyte layer between the active material electrodes. Each active material electrode may have a plurality of folded sections and planar sections to increase the ESD capacity, for example, by increasing number of interfaces within each cell segment.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/147,725, filed Jan. 27, 2009, and U.S. Provisional Application No. 61/181,194, filed May 26, 2009, both of which are hereby incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

This invention relates generally to energy storage devices (ESDs) and, more particularly, this invention relates to stacked ESDs with electrode folds.

BACKGROUND OF THE INVENTION

Bi-polar ESDs may provide an increased discharge rate and a higher voltage potential between their external connectors than standard wound or prismatic cells, and are therefore in high demand for certain applications. Conventional ESDs have been manufactured as either a wound cell structure that has only two electrodes or a standard prismatic cell structure that has many plate sets in parallel. In both of these types, the electrolyte is shared everywhere within the ESD. The wound cell structure and prismatic cell structure both suffer from high electrical resistances due to their electrical paths having to cross multiple connections and span significantly long distances to cover the complete circuit from one cell to the next in a series arrangement.
In addition, both the wound cell and prismatic cell structures require electrodes having relatively high mechanical stability for assembly, processing, and packaging of the electrodes into the cell. The wound cell electrode must be sufficiently resilient to avoid the stress-related defects associated with winding, as it is bent to a range of curvatures during the winding and packaging process, which can impart structural damage and negatively affect ESD performance. Prismatic electrodes are typically flat and are generally not subjected to the stresses imparted by the winding process of the wound cell structure. Prismatic electrodes, however, require additional connection components between plates having the same polarity within a cell.
Accordingly, it would be desirable to provide an ESD that avoids the process of winding and thereby the stress-related defects of winding. Further, it would be desirable to provide an ESD having electrodes along a folded mechanical compliment common collector, or electron transfer path, to eliminate the need for additional connection components as in the prismatic cell structure.
With the increasing use of ESDs for various applications, the capacity of these devices has become an important factor. ESD capacity is a measure of the charge stored by the ESD and is a component of the maximum amount of energy that can be extracted from the ESD. An ESD's capacity may be related to the mass of active materials contained in the ESD and by the number of interfaces between the electrodes in the ESD. In conventional wound cell and prismatic cell structures, the capacity is increased by adding more material (e.g., by adding more electrodes or increasing the size of the electrodes). This increases the size of the ESD and may add a considerable amount of mass to the ESD relative to the resulting increase in the capacity.
Accordingly, it would be desirable to provide a stacked bi-polar ESD having cells with increased capacity while minimizing the mass and volume of the ESD. Further, it would be desirable to provide a stacked bi-polar ESD having cells with an increased number of interfaces between electrodes.

SUMMARY OF THE INVENTION

In view of the foregoing, apparatus and methods are provided for stacked ESDs having increased capacity and folded electrodes.
In accordance with an embodiment, there is provided an ESD having a first conductive substrate and a second conductive substrate provided in a stacking direction. A first active material may be provided between the first conductive substrate and the second conductive substrate, and a second active material may be provided between the first conductive substrate and the second conductive substrate. Each of the first and second active materials may be folded and may have a plurality of planar sections orthogonal to the stacking direction, where each planar section may be coupled to an adjoining planar section by a folded section, and where each respective planar section of the first active material may interface with a respective planar section of the second active material.
In some embodiments of the present invention powder packed electrodes for an energy storage device may be provided. Active powders may be dry-packed into a substrate, and the active powders may be wetted with a wetting agent to ensure an even distribution and surface gradient of the substrate. The active powders may be over-coated with a binder layer on the surface of the substrate. The chemical resistance of the binder layer may hold the active powders in place while allowing the transportation of electrolyte ions to and from the substrate. In some embodiments, the substrate may be coupled to a common collector that may be folded to form a folded electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

FIG. 1 shows a schematic cross-sectional view of a structure of a bi-polar electrode unit (BPU) according to an embodiment of the invention;

FIG. 2 shows a schematic cross-sectional view of a structure of a stack of BPUs of FIG. 1 according to an embodiment of the invention;

FIG. 3 shows a schematic cross-sectional view of a structure of a stacked bi-polar ESD according to an embodiment of the invention;

FIG. 4 shows a schematic cross-sectional view of a structure of a stack of BPUs having thickened electrodes according to an embodiment of the invention;

FIG. 5 shows a schematic cross-sectional view of a structure of a stack of BPUs having electrode folds according to an embodiment of the invention;

FIG. 6 shows a schematic cross-sectional view of a structure of a stack of BPUs having electrode folds according to an embodiment of the invention;

FIG. 7 shows a perspective view of an origami electrode fold according to an embodiment of the present invention;

FIG. 8 shows a side elevation view of the origami electrode fold of FIG. 7 according to an embodiment of the invention;

FIGS. 9A and 9B show a top plan view and a side elevation view, respectively, of a structure of an active material electrode layer according to an embodiment of the invention;

FIG. 9C shows a side elevation view of the active material electrode layer of FIGS. 9A-9B that has been folded according to an embodiment of the invention;

FIGS. 10A and 10B show a top plan view and a side elevation view, respectively, of a structure of an active material electrode layer according to an embodiment of the invention;

FIG. 10C shows a side elevation view of the active material electrode layer of FIGS. 10A-10B that has been folded according to an embodiment of the invention; and

FIG. 11 shows an illustrative flow diagram for powder packing an electrode according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Apparatus and methods are provided for stacked energy storage devices (ESDs) with increased capacity, and are described below with reference to FIGS. 1-11. The present invention relates to ESDs such as, for example, batteries, capacitors, or any other suitable electrochemical energy or power storage devices which may store and/or provide electrical energy or current. It will be understood that while the present invention is described herein in the context of a stacked bi-polar ESD, the concepts discussed are applicable to any intercellular electrode configuration including, but not limited to, parallel plate, prismatic, folded, wound and/or bi-polar configurations, any other suitable configuration, or any combinations thereof.
Various types of ESDs with sealed cells in a stacked formation have been developed that are able to provide higher discharge rates and higher voltage potentials between external connectors than that of standard wound or prismatic ESDs, and are therefore in high demand for certain applications. Certain types of these ESDs with sealed cells in a stacked formation have been developed to generally include a stack of independently sealed pairs of mono-polar electrode units (MPUs). Each of these MPUs is provided with either a positive active material electrode layer or a negative active material electrode layer coated on a first side of a current collector. An MPU with a positive active material electrode layer (i.e., a positive MPU) and an MPU with a negative active material electrode layer (i.e., a negative MPU) has an electrolyte layer therebetween for electrically isolating the current collectors of those two MPUs. The current collectors of this pair of positive and negative MPUs, along with the active material electrode layers and electrolyte therebetween, are sealed as a single cell or cell segment. An ESD that includes a stack of such cells, each having a positive MPU and a negative MPU, shall be referred to herein as a “stacked mono-polar” ESD.
The side of the current collector of the positive MPU not coated with an electrode layer in a first cell is electrically coupled to the side of the current collector of the negative MPU not coated with an electrode layer in a second cell, such that the first and second cells are in a stacked formation. The series configuration of these cell segments in a stack may cause the voltage potential to be different between current collectors. However, if the current collectors of a particular cell contact each other or if the common electrolyte of the two MPUs in a particular cell is shared with any additional MPU in the stack, the voltage and energy of the ESD would fade (i.e., discharge) quickly to zero. Therefore, a stacked mono-polar ESD independently seals the electrolyte of each of its cells from each of its other cells.
Other types of ESDs with sealed cells in a stacked formation have been developed to generally include a series of stacked bi-polar electrode units (BPUs). Each of these BPUs is provided with a positive active material electrode layer and a negative active material electrode layer coated on opposite sides of a current collector. Any two BPUs can be stacked on top of one another with an electrolyte layer provided between the positive active material electrode layer of one of the BPUs and the negative active material electrode layer of the other one of the BPUs for electrically isolating the current collectors of those two BPUs. The current collectors of any two adjacent BPUs, along with the active material electrode layers and electrolyte therebetween, may also be a sealed single cell or cell segment. An ESD that includes a stack of such cells, each having a portion of a first BPU and a portion of a second BPU, shall be referred to herein as a “stacked bi-polar” ESD.
While the positive side of a first BPU and the negative side of a second BPU may form a first cell, the positive side of the second BPU may likewise form a second cell with the negative side of a third BPU or the negative side of a negative MPU, for example. Therefore, an individual BPU may be included in two different cells of a stacked bi-polar ESD. The series configuration of these cells in a stack may cause the voltage potential to be different between current collectors. However, if the current collectors of a particular cell contact each other or if the common electrolyte of the two BPUs in a first cell is shared with any other cell in the stack, the voltage and energy of the ESD would fade (i.e., discharge) quickly to zero.
Conventional stacked bi-polar ESDs use flat electrode plates. By using flat plates and isolating them by use of an edge seal, cells in a stacked electrochemical ESD may operate substantially independently. As the independent cells are charged and discharged, slight pressure differences may develop between adjacent cells. If the pressure difference between the adjacent cells exceeds a few pounds per square inch, then the flat electrode may deflect from the first cell towards the second cell. This deflection may strain the separator material of the second cell, creating a “hot spot” where a short circuit may develop. Because the physical components and the chemistry of individual cells will generally be slightly different from one another, pressure differentials between cells will generally exist.
FIG. 1 shows an illustrative “flat plate” bi-polar electrode unit or BPU 102, in accordance with an embodiment of the present invention. Flat plate structures for use in stacked cell ESDs are discussed in more detail in Ogg et al. U.S. patent application Ser. No. 11/417,489, and Ogg et al. U.S. patent application Ser. No. 12/069,793, both of which are hereby incorporated by reference herein in their entireties. BPU 102 may include a positive active material electrode layer 104 that may be provided on a first side of an impermeable conductive substrate or current collector 106, and a negative active material electrode layer 108 that may be provided on the other side of impermeable conductive substrate 106 (see, e.g., Fukuzawa et al., U.S. Pat. No. 7,279,248, issued Oct. 9, 2007, which is hereby incorporated by reference herein in its entirety).
It will be understood that the bi-polar electrode may have any suitable shape or geometry. For example, in some embodiments of the present invention, the “flat plate” BPU may alternatively, or additionally, be a “dish-shaped” electrode. This may reduce pressures that may develop during operation of a bi-polar ESD. Dish-shaped and pressure equalizing electrodes are discussed in more detail in West et al. U.S. patent application Ser. No. 12/258,854, which is hereby incorporated by reference herein in its entirety.
FIG. 2 shows a schematic cross-sectional view of a structure of a stack of BPUs (see, e.g., BPU 102 of FIG. 1) in accordance with an embodiment of the present invention. For example, multiple BPUs 202 may be stacked substantially vertically into a stack 220, with an electrolyte layer 210 that may be provided between two adjacent BPUs 202, such that positive electrode layer 204 of one BPU 202 may be opposed to negative electrode layer 208 of an adjacent BPU 202 via electrolyte layer 210. Each electrolyte layer 210 may include a separator (not shown) that may hold an electrolyte. The separator may electrically separate the positive electrode layer 204 and negative electrode layer 208 adjacent thereto, while allowing ionic transfer between the electrode units, as described in more detail below.
With continued reference to the stacked state of BPUs 202 in FIG. 2, for example, the components included in positive electrode layer 204 and substrate 206 of a first BPU 202, the negative electrode layer 208 and substrate 206 of a second BPU 202 adjacent to the first BPU 202, and the electrolyte layer 210 between the first and second BPUs 202 shall be referred to herein as a single “cell” or “cell segment” 222. Each impermeable substrate 206 of each cell segment 222 may be shared by the applicable adjacent cell segment 222.
As shown in FIG. 3, for example, positive and negative terminals may be provided along with stack 20 of one or more BPUs 2 a-d to constitute a stacked bi-polar ESD 50 in accordance with an embodiment of the invention. A positive mono-polar electrode unit or MPU 12, that may include a positive active material electrode layer 14 provided on one side of an impermeable conductive substrate 16, may be positioned at a first end of stack 20 with an electrolyte layer provided (i.e., electrolyte layer 10 e), such that positive electrode layer 14 of positive MPU 12 may be opposed to a negative electrode layer (i.e., layer 8 d) of the BPU (i.e., BPU 2 d) at that first end of stack 20 via the electrolyte layer 10 e. A negative mono-polar electrode unit or MPU 32, that may include a negative active material electrode layer 38 provided on one side of an impermeable conductive substrate 36, may be positioned at the second end of stack 20 with an electrolyte layer provided (i.e., electrolyte layer 10 a), such that negative electrode layer 38 of negative MPU 32 may be opposed to a positive electrode layer (i.e., layer 4 a) of the BPU (i.e., BPU 2 a) at that second end of stack 20 via the electrolyte layer 10 a. MPUs 12 and 32 may be provided with corresponding positive and negative electrode leads 13 and 33, respectively.
It should be noted that the substrate and electrode layer of each MPU may form a cell segment with the substrate and electrode layer of its adjacent BPU 2 a/2 d, and the electrolyte layer 10 a/10 e therebetween, as shown in FIG. 3, for example (see, e.g., segments 22 a and 22 e). The number of stacked BPUs 2 a-d in stack 20 may be one or more, and may be appropriately determined in order to correspond, for example, to a desired voltage for ESD 50. Each BPU 2 a-d may provide any desired potential, such that a desired voltage for ESD 50 may be achieved by effectively adding the potentials provided by each component BPU 2 a-d. It will be understood that each BPU 2 a-d need not provide identical potentials.
In some embodiments, bi-polar ESD 50 may be structured so that BPU stack 20 and its respective positive and negative MPUs 12 and 32 may be at least partially encapsulated (e.g., hermetically sealed) into an ESD case or wrapper 40 under reduced pressure. MPU conductive substrates 16 and 36 (or at least their respective electrode leads 13 and 33) may be drawn out of ESD case 40, so as to mitigate impacts from the exterior upon usage and to prevent environmental degradation, for example.
In order to prevent electrolyte of a first cell segment (see, e.g., electrolyte layer 10 a of cell segment 22 a) from combining with the electrolyte of another cell segment (see, e.g., electrolyte layer 10 b of cell segment 22 b), gaskets or sealants may be stacked with the electrolyte layers between adjacent electrode units to seal electrolyte within its particular cell segment. A gasket or sealant may be any suitable compressible or incompressible solid or viscous material, any other suitable material, or combinations thereof, for example, that may interact with adjacent electrode units of a particular cell to seal electrolyte therebetween. In one suitable arrangement, as shown in FIG. 3, for example, the bi-polar ESD of the invention may include gaskets or seals 60 a-e that may be positioned as a barrier about electrolyte layers 10 a-e and active material electrode layers 4 a-d/14 and 8 a-d/38 of each cell segment 22 a-e. The gasket or sealant may be continuous and closed and may seal electrolyte between the gasket and the adjacent electrode units of that cell (i.e., the BPUs or the BPU and MPU adjacent to that gasket or seal). The gasket or sealant may provide appropriate spacing between the adjacent electrode units of that cell, for example.
In sealing the cell segments of stacked bi-polar ESD 50 to prevent electrolyte of a first cell segment (see, e.g., electrolyte layer 10 a of cell segment 22 a) from combining with the electrolyte of another cell segment (see, e.g., electrolyte layer 10 b of cell segment 22 b), cell segments may produce a pressure differential between adjacent cells (e.g., cells 22 a/22 b) as the cells are charged and discharged. Equalization valves may be provided to substantially decrease the pressure differences thus arising. Equalization valves may operate as a semi-permeable membrane or rupture disk, either mechanically or chemically, to allow the transfer of a gas and to substantially prevent the transfer of electrolyte. An ESD may have BPUs having any combination of equalization valves. Pressure equalization valves are discussed in more detail in West et. al U.S. patent application Ser. No. 12/258,854, which is hereby incorporated by reference herein in its entirety.
FIGS. 4-6 show various embodiments of the present invention that may be used, for example, to increase the capacity of an ESD.
FIG. 4 shows a schematic cross-sectional view of a structure of a stack 420 of two cell segments 422 a-b according to an embodiment of the invention. As shown in FIG. 4, for example, each cell segment 422 a-b may include a positive active material electrode layer 404 and a negative active material electrode layer 408 with an electrolyte layer provided therebetween. Impermeable conductive substrate or current collector 406 c may be at a first end of stack 420, and conductive substrate 406 a may be at a second end of stack 420. A stacking direction may be defined, using conductive substrates 406 c and 406 a, as the direction from the first end of stack 420 to the second end of stack 420. With continued reference to the stacked state of FIG. 4, for example, the components between and including conductive substrate 406 a and conductive substrate 406 b may be included in cell segment 422 a. Similarly, the components between and including conductive substrate 406 b and conductive substrate 406 c may be included in cell segment 422 b.
In the stack of FIG. 4, for example, positive electrode layer 404 and negative electrode layer 408 may be separated by a gap distance 415. Gap distance 415 may be any suitable distance. For example, gap distance 415 may be any suitable distance that minimizes internal resistance while restricting electron transport between electrode surfaces. For example, suitable gap distances may be design specific and may be 0 mils, 5 mils, 10 mils, or greater. Gap distances may be related, for example, to the closing force of the ESD assembly, the electrode thickness, and the electrode loading of active materials. Gap distances may be optimized, for example, to minimize electrode separation without causing excess force on the electrodes, or the separator, during charge and discharge cycling. An ESD incorporating variable volume containment may independently adjust cells to set a respective gap distance to compensate for the volumetric changes of electrodes during cycling. Variable volume containment is described in more detail in West et al. U.S. patent application Ser. No. ______ (Attorney Docket No. 106210-0005-101), filed Jan. 27, 2010, which is hereby incorporated by reference herein in its entirety.
In some embodiments, for example, to increase the ESD capacity of stack 420, positive electrode layer 404 and negative electrode layer 408 may be thickened by increasing height 404 h or height 408 h, or both, so that gap distance 415 may be relatively small, for example, compared to the gap distance between positive electrode layer 204 and negative electrode layer 208 of FIG. 2.
Thickening positive electrode layer 404 and/or negative electrode layer 408 may yield a loss in conductivity, however, because the anode and cathode interfacial area may not substantially change (i.e., the interfacial surface area of positive electrode layer 404 and negative electrode layer 408 may not substantially change when either or both electrode layers are thickened), yet the thickened electrodes may lead to longer paths for ion and electron flow, thereby increasing the internal resistance.
FIG. 5 shows a schematic cross-sectional view of a structure of a stack 520 of two cell segments 522 a-b according to an embodiment of the invention. FIG. 5 illustrates another approach for increasing the capacity of an ESD by providing, for example, what shall be referred to herein as a “z-fold” electrode. As shown in FIG. 5, for example, each cell segment 522 a-b may include a positive active material electrode layer 504 and a negative active material electrode layer 508 with an electrolyte layer provided between each interface of the active materials (see, e.g., interfaces 517, 518, and 519). Impermeable conductive substrate or current collector 506 c may be at a first end of stack 520, and conductive substrate 506 a may be at a second end of stack 520. A stacking direction may be defined, using conductive substrates 506 c and 506 a, as the direction from the first end of stack 520 to the second end of stack 520. With continued reference to the stacked state of FIG. 5, for example, the components between and including conductive substrate 506 a and conductive substrate 506 b may be included in cell segment 522 a. Similarly, the components between and including conductive substrate 506 b and conductive substrate 506 c may be included in cell segment 522 b.
Providing a z-fold electrode may substantially increase the number of interfaces between positive electrode layer 504 and negative electrode layer 508 (e.g., interface 518) in a given cell segment 522 a-b. For example, there may be a greater number of interfaces between positive electrode layer 504 and negative electrode layer 508 in cell segment 522 a than the number of interfaces in a cell segment in FIG. 4, which shows only a single interface in each cell segment (see, e.g., cell segment 422 a). The interfaces of the z-fold electrode may increase the surface area where electrodes contact each other and the current collectors, thereby decreasing the internal resistance of the ESD since the resistance is inversely proportional to surface area.
As illustrated in FIG. 5, interfaces between positive electrode layer 504 and negative electrode layer 508 may be provided that may not be balanced, or may be unused, within a cell segment. For example, interface 517 and interface 519 may be between electrode layers having the same polarity. In particular, interface 517 may be between two planar surfaces of positive electrode layer 504, and interface 519 may be between two planar surfaces of negative electrode layer 508.
The edges of the individual electrodes may be relatively sharp and may pierce the separator if not preferably sealed by an insulating material. The edges of the electrodes may also be insulated by an insulating material so as not to touch the inside edges of the substrates. As number of folds increases, quality control becomes more important as individual cells are preferably matched in weight, thickness, and packing uniformity, for example, in order to limit dense spots.
FIG. 6 shows a cross-sectional segment view of a structure of a stack 620 of two cell segments 622 a-b according to an embodiment of the invention. FIG. 6 illustrates another approach for increasing the capacity of an ESD by providing, for example, an “origami” electrode fold. As shown in FIG. 6, for example, cell segments 622 a-b may include a positive active material electrode layer 604 and a negative active material electrode layer 608 with an electrolyte layer provided between each interface of the active materials (see, e.g., interface 621). Impermeable conductive substrate or current collector 606 c may be at a first end of stack 620, and conductive substrate 606 a may be at a second end of stack 620. A stacking direction may be defined, using conductive substrates 606 c and 606 a, as the direction from the first end of stack 620 to the second end of stack 620. With continued reference to the stacked state of FIG. 6, for example, the components between and including conductive substrate 606 a and conductive substrate 606 b may be included in cell segment 622 a. Similarly, the components between and including conductive substrate 606 b and conductive substrate 606 c may be included in cell segment 622 b.
Providing an origami electrode may substantially increase the number of interfaces (e.g., interface 621) between positive electrode layer 604 and negative electrode layer 608 in a given cell segment 622 a-b. For example, there may be a greater number of interfaces between positive electrode layer 604 and negative electrode layer 608 in cell segment 622 a than the number of interfaces in a cell segment in FIG. 4, which shows only a single interface in each cell segment (see, e.g., cell segment 422 a of FIG. 4). Further, there may be a greater number of interfaces between electrode layers of opposite polarity than that of FIG. 5, at least because some of the interfaces of FIG. 5 are between electrode layers having the same polarity (see, e.g., interfaces 517 and 519 of FIG. 5).
As shown in FIG. 6, for example, interface 621 may be between positive electrode layer 604 and negative electrode layer 608. An advantage of the origami electrode embodiment may be that each and every interface within a cell may be between electrode layers of opposite polarity (i.e., there may be no interfaces between electrode layers having the same polarity, unlike interfaces 517 and 519 of FIG. 5). ESD capacity and electrochemical transport properties may be dependent, for example, on the number of interfaces between electrodes of opposite polarity. Because the origami electrode may increase the number of interfaces between electrodes of opposite polarity in a given cell, this configuration may substantially increase the capacity of the ESD. This may allow the origami electrode fold to increase the ESD capacity by increasing the anode to cathode interfacial area within a cell segment.
FIG. 7 shows a perspective view of an origami electrode fold 700 according to an embodiment of the present invention. For example, FIG. 7 may be a more detailed perspective view of various segments of the origami electrode fold of FIG. 6. As shown in FIG. 7, for example, positive active material electrode layer 704 and negative active material electrode layer 708 may include a plurality of planar sections and folded portions. Origami electrodes 700 of FIG. 7 may be provided, for example, in a cell segment of an ESD (e.g., cell segment 22 b of FIG. 3).
FIG. 8 shows a side elevation view of the origami electrode fold of FIG. 7 according to an embodiment of the invention. A first planar section 751 a of negative electrode layer 708 may include a top planar surface 742 and a bottom planar surface 744. First planar section 751 a may be coupled to a second planar section 751 b by a first folded portion 752 a. Similarly, second planar section 751 b may be coupled to a third planar section 751 c by a second folded portion 752 b. There may be a similar number of planar sections and folded portions in the corresponding positive electrode layer 704. Although only three planar sections and two folded portions are shown for each of positive electrode layer 704 and negative electrode layer 708, it will be understood that any suitable number of planar sections coupled to folded portions may be provided. For example, in order to provide an ESD with a desired capacity there may be a preferred number of interfaces within some cells of the ESD.
The planar sections of each electrode layer may be provided in a plane that is substantially orthogonal to a stacking direction of the ESD. For example, each planar section 751 a-c of FIG. 7 may lie in a plane that is orthogonal to a stacking direction of the ESD defined by axis 741.
In some embodiments, planar sections may be provided in any other suitable direction. For example, planar sections may be provided in a plane that faces radially outwardly from the stacking direction defined by axis 741 (i.e., the planar sections may lie substantially parallel to the stacking direction). It will be understood that there may be any suitable number of possible shapes of electrode layers 704 and 708 provided where each and every interface may be between electrode layers having opposite polarity. For example, although the cross-sectional areas of the planar sections of FIGS. 7 and 8 are shown as being substantially rectangular, the planar sections may be circular, triangular, hexagonal, or any other desired shape or combinations thereof.
Top planar surface 742 of negative electrode layer 708 may be coupled to a first conductive substrate located within a cell segment (see, e.g., conductive substrate 606 a of FIG. 6) and bottom planar surface 748 of positive electrode layer 704 may be coupled to a second conductive substrate located within the same cell segment (see, e.g., conductive substrate 606 b of FIG. 6). An electrode may be connected to a conductive substrate using various approaches. In an embodiment, an electrode layer may be coupled to a conductive substrate using a pressure contact. For example, spring contacts may allow for an electrical contact without soldering. By avoiding solder fatigue, spring contacts may be resistant against shock, vibration, and corrosion, for example, and may provide relatively high temperature cycling. By omitting solder layers, for example, there may be a relatively lower resistance compared to leaded connections. In other embodiments, an electrode layer may be spot welded or sintered to a conductive substrate.
As discussed above in connection with FIGS. 6-8, an origami electrode may provide a plurality of interfaces between the positive and negative electrode layers within a cell segment. For example, bottom planar surface 744 of negative electrode layer 708 and top planar surface 746 of positive electrode layer 704 may be one of five interfaces of the origami electrodes of FIG. 8. It will be understood that there may be any suitable number of interfaces provided in a cell segment.
In an embodiment of the present invention, the positive active material electrode layer (see, e.g., positive electrode layer 704) and/or negative active material electrode layer (see, e.g., negative electrode layer 708) may include a single active material electrode sheet, respectively, that is folded at a plurality of folded portions in order to make the structure of the origami electrode. A similar approach may be used to make the structure of the z-fold electrode or any other suitable folded electrode configuration. Alternatively, in some embodiments the positive electrode layer and/or negative electrode layer may include one or more electrodes provided along a common collector or what shall be referred to herein as an “electronic raceway,” that may provide an electron transfer path.
FIGS. 9A and 9B show a top plan view and a side elevation view, respectively, of a structure of an active material electrode layer according to an embodiment of the invention. As shown in FIGS. 9A and 9B, for example, active material electrode layer 904 may include electrode segments 905 a-c coupled to a common collector or electronic raceway 901, which may serve as an electron transfer path. Although three exemplary electrode segments are shown (i.e., electrode segments 905 a-c), it will be understood that any suitable number of electrode segments may be provided along electronic raceway 901. For example, active material electrode layer 904 may include one more electrode segments according to any preferred design criteria for the ESD.
The portions of electronic raceway 901 that are not coupled to electrode segments 905 a-c may be folded into folded portions 952 a and 952 b as shown in FIG. 9C to make a folded electrode. Each electrode segment 905 a-c may correspond to a respective planar section of the active material electrode when it is folded, for example, into the origami or z-fold configuration. For example, electrode segment 905 a may correspond to planar section 951 a, electrode segment 905 b may correspond to planar section 951 b, and electrode segment 905 c may correspond to planar section 951 c.
In some embodiments, a separator may be provided in the electrolyte layer between the active material electrode layers. For example, the separator may electrically separate the positive active material electrode layer (see, e.g., positive electrode layer 204) and negative active material electrode layer adjacent thereto (see, e.g., negative electrode layer 208), while allowing ionic transfer between the electrode units. In some embodiments a separator may alternatively, or additionally, be provided around each electrode segment (e.g., electrode segments 905 a-c). For example, a separator sleeve may be ultrasonically welded around electrode segment 905 a. Any other suitable technique, or combination of techniques, may be used to fit and/or fasten the separator sleeve around electrode segment 905 a.
As shown, each of electrode segments 905 a-c may be of the same polarity (i.e., positive or negative) and may have a substantially rectangular cross-section. It will be understood that there may be any suitable number of possible shapes of electrode segments 905 a-c provided on electronic raceway 901. For example, although the cross-sectional areas of the electrode segments of FIGS. 9A-9C are shown as being substantially rectangular, the electrode segments may be circular, triangular, hexagonal, or any other desired shape or combinations thereof.
FIGS. 10A-10C show a structure of an active material electrode layer having circular electrode segments according to an embodiment of the invention. As shown in FIGS. 10A-10C, for example, active material electrode layer 1004 may include electrode segments 1005 a-c coupled to a common collector or electronic raceway 1001, which may serve as an electron transfer path. Active material electrode layer 1004 may be folded, where each electrode segment 1005 a-c may correspond to a respective planar section 1051 a-c of the folded electrode, and the portions of electronic raceway 1001 that are not coupled to electrode segments 1005 a-c may be folded into folded portions 1052 a and 1052 b as shown in FIG. 10C to make a folded electrode.
The origami electrodes of the present invention may help maintain the inter-electrode spacing of the ESD. As defined herein, “inter-electrode spacing” is the distance between active material electrode layers in a stacked bi-polar ESD. This may be applied, for example, to the distance between a positive and negative electrode in a cell that only contains one positive and one negative electrode. In some embodiments, this may be applied to a cell with multiple electrode sets or segments within the same cell. For cells with multiple electrodes or electrode segments, there may be multiple inter-electrode spacings.
When an ESD having origami electrodes expands or contracts along a stacking direction or axis (see, e.g., axis 741 of FIG. 8), the displacement of a given planar electrode section (e.g., planar section 751 b of FIG. 8) may relate to the total distance moved divided by the total number of folds, such that changes in the inter-electrode spacing of the ESD may be relatively minimal in the case of expansion and/or contraction of the electrodes along the stacking axis during operation of the ESD. Maintaining inter-electrode spacing in ESDs using variable volume containment is discussed in more detail in West et al. U.S. patent application Ser. No. ______ (Attorney Docket No. 106210-0005-101), filed Jan. 27, 2010, which is hereby incorporated by reference herein in its entirety.
It will be understood that the cell segments of a given ESD of the present invention may include positive and negative active material electrode layers of any of the configurations as discussed above in connection with FIGS. 1-10, or any other suitable configurations, or combinations thereof. For example, cell segment 22 a of FIG. 3 may include a thickened electrode configuration, cell segment 22 b may include a z-fold electrode configuration, and cell segment 22 c may include an origami electrode fold configuration.
In accordance with embodiments of the present invention, any suitable technique for producing any of the active material electrode layers as discussed above in connection with FIGS. 1-10 may be used.
FIG. 11 shows illustrative flow diagram 1100 for a process according to an embodiment of the present invention for powder packing an active material electrode layer. This generally may involve the steps of dry packing active powders into a substrate, wetting the dry packed powders with a wetting agent, and over-coating the dry packed powders with a binder layer.
In dry packing step 1102, the active material electrode powders may be dry packed into a substrate or conductive matrix. The substrate may be any electrically conductive matrix that may hold active materials. For example, the substrate may be nickel foam.
In wetting step 1104, the dry packed powders may be wetted with a wetting agent to reduce viscosity and ensure a substantially even distribution and surface gradient, which may allow relatively uniform transport of the active materials from the surface of the conductive matrix into the bulk of the conductive matrix. This step may reduce the surface gradient, for example, to allow relatively easier impregnation of the active material into the conductive matrix. It will be understood that the active material electrode powder may be wetted with a wetting agent before it is packed into the conductive matrix, or after, or both. Further, it will be understood that the active material electrode powders may be wetted using any suitable wetting agent, such as distilled water, alcohol, or any other suitable agent, or any combination thereof.
In some embodiments, a wetting agent may be used that may substantially dissolve off of the conductive matrix. This may ensure that particulates that may be non-reactive (e.g., that do not contribute to the electrical performance of the ESD), and/or particulates that may degrade the performance of the ESD, are not left as a by-product in the substrate mix. Alternatively, or additionally, the wetting agent may be baked off. For example, solvents such as water, ispropyl alcohol, ethanol, and N-Methylpyrroliodone (NMP), or any other suitable agent, or combinations thereof, may be evaporated or baked off in order to leave few or substantially no residuals.
In some embodiments, it may be desirable to leave a residual element after dissolving or baking off most of the wetting agent if the residual element enhances the performance of the conductive matrix. This may be useful, for example, when preparing electrodes using a slurry impregnation process, where a relatively low viscosity slurry that includes a hydrophilic binder (e.g., PVA) may be used to increase the surface gradient and help impregnation of the electrodes. The binder may primarily consist of water, which when dissolved or baked off after impregnation, may leave a small amount of binder material that helps enhance the mechanical properties of active materials in the electrode matrix. For example, the binder material may help keep the active materials in place within the electrode matrix. During cycling, the active materials may change in volume, and the binder material may help to prevent the active materials from being pushed out of the electrode matrix, causing early failure modes of the ESD.
In over-coating step 1106, the dry packed active material electrode powders may be over-coated with a binder layer on the surface of the conductive matrix. The chemical resistance of the binder layer may hold the dry packed powders in place while substantially allowing the transportation of electrolyte ions to and from the active materials of the conductive matrix.
A binder may be used, for example, to bind separate particles together or facilitate adhesion to a surface. If a binder is mixed with active material electrode powders before the powders are pasted onto a substrate or conductive matrix, the active surfaces may be coated with a substantially non-conducting material. This may potentially reduce conductivity and may reduce the chemical kinetics of the ESD, and a given cell segment and/or the ESD may have reduced electrical and chemical performance. If no binder is used then the active material electrode powders may be free to move throughout the cell and across the separator, and may form hard shorts and/or soft shorts which may hinder ESD performance or even destroy the cell.
In some embodiments, nickel foam may be used as a conductive matrix for both the positive electrode layer and the negative electrode layer (see, e.g., positive electrode layer 704 and negative electrode layer 708 of FIG. 7). Traditionally, nickel foam has been used in positive nickel hydroxide Ni(OH)₂electrodes for nickel-metal hydride (NiMH) ESDs. This is due to the relatively low conductivity of the positive material. However, nickel foam may be used for both the positive and negative electrodes. This may enhance the interfaces in the respective conductive matrices.
It should be understood that the steps of flow diagram 1100 are merely illustrative. Any of the steps of flow diagram 1100 may be modified, omitted, or rearranged, two or more of the steps may be combined, or any additional steps may be added, without departing from the scope of the present invention.
Producing the origami electrode of the present invention may generally involve the steps of providing an active material electrode layer and folding the layer.
When an origami electrode fold is employed (e.g., origami electrode 700 of FIGS. 7 and 8), the positive and negative active material electrode layers may include a flexible substrate or conductive matrix as the support structure for the active materials. In some embodiments, the conductive matrix may be nickel foam, however, any other suitable flexible and/or perforated metallic conductive matrix, or combinations thereof, may also be used as the active material host material. The foam matrix may be sized at the folded portions prior to impregnating and folding the foam. This may substantially prevent the nickel foam from breaking due to the relatively brittle material properties of the nickel foam.
Inserting tabs and/or attaching the electronic raceway to the electrode segments (see, e.g., electrode segments 905 a-c of FIG. 9B) may create relatively sharp edges, which may in turn penetrate the insulating separator, as previously discussed. A conductive material resistant to the electrolyte in the cell including, for example, nickel, nickel-plated copper, stainless steel, nickel-plated steel, or any other suitable material, or combinations thereof, may be used to attach the electrode segments of the continuous electronic raceway strip, which may then be folded to make up the folded electrode stack. The material between the individual electrode segments (e.g., electronic raceway 901) may be sized to contact separate electrode segments and/or to minimize internal resistance between electrodes of the same potential (i.e., positive or negative). The material connecting electrode segments of the same potential may have a relatively greater mechanical strength than the electrode segments, for example, in order to be less susceptible to breaking due to folding, thereby substantially preventing potential creep stresses at the edges of the material.
The substrates used to form the electrode units of the invention (e.g., substrates 6 a-d, 16, and 36) may be formed of any suitable conductive and impermeable or substantially impermeable material, including, but not limited to, a non-perforated metal foil, aluminum foil, stainless steel foil, cladding material including nickel and aluminum, cladding material including copper and aluminum, nickel plated steel, nickel plated copper, nickel plated aluminum, gold, silver, any other suitable material, or combinations thereof, for example. Each substrate may be made of two or more sheets of metal foils adhered to one another, in certain embodiments. The substrate of each BPU may typically be between 0.025 and 5 millimeters thick, while the substrate of each MPU may be between 0.025 and 10 millimeters thick and act as terminals to the ESD, for example. Metalized foam, for example, may be combined with any suitable substrate material in a flat metal film or foil, for example, such that resistance between active materials of a cell segment may be reduced by expanding the conductive matrix throughout the electrode.
The positive electrode layers provided on these substrates to form the electrode units of the invention (e.g., positive electrode layers 4 a-d and 14) may be formed of any suitable active material, including, but not limited to, nickel hydroxide (Ni(OH)₂), zinc (Zn), any other suitable material, or combinations thereof, for example. The positive active material may be sintered and impregnated, coated with an aqueous binder and pressed, coated with an organic binder and pressed, or contained by any other suitable technique for containing the positive active material with other supporting chemicals in a conductive matrix. The positive electrode layer of the electrode unit may have particles, including, but not limited to, metal hydride (MH), palladium (Pd), silver (Ag), any other suitable material, or combinations thereof, infused in its matrix to reduce swelling, for example. This may increase cycle life, improve recombination, and reduce pressure within the cell segment, for example. These particles, such as MH, may also be in a bonding of the active material paste, such as Ni(OH)₂, to improve the electrical conductivity within the electrode and to support recombination.
The negative electrode layers provided on these substrates to form the electrode units of the invention (e.g., negative electrode layers 8 a-d and 38) may be formed of any suitable active material, including, but not limited to, MH, Cd, Mn, Ag, any other suitable material, or combinations thereof, for example. The negative active material may be sintered, coated with an aqueous binder and pressed, coated with an organic binder and pressed, or contained by any other suitable technique for containing the negative active material with other supporting chemicals in a conductive matrix, for example. The negative electrode side may have chemicals including, but not limited to, Ni, Zn, Al, any other suitable material, or combinations thereof, infused within the negative electrode material matrix to stabilize the structure, reduce oxidation, and extend cycle life, for example.
Various suitable binders, including, but not limited to, organic carboxymethylcellulose (CMC) binder, Creyton rubber, PTFE (Teflon), any other suitable material, or combinations thereof, for example, may be mixed with the active material layers to hold the layers to their substrates. Ultra-still binders, such as 200 ppi metal foam, may also be used with the stacked ESD constructions of the invention.
The common collector or electronic raceway used to form the active material electrode layers in some embodiments of the invention (e.g., electronic raceway 901 a) may be formed of any suitable conductive and impermeable or substantially impermeable material, including, but not limited to, a non-perforated metal foil, aluminum foil, stainless steel foil, cladding material including nickel and aluminum, cladding material including copper and aluminum, nickel plated steel, nickel plated copper, nickel plated aluminum, gold, silver, any other suitable conductive and/or mechanically durable material, or combinations thereof, for example. In some embodiments, each electronic raceway may be made of two or more sheets of metal foils adhered to one another. As discussed above, the electronic raceway may have a relatively high mechanical strength in order to resist potentially negative stress-effects from folding.
The separator of each electrolyte layer of the ESD of the invention may be formed of any suitable material that electrically isolates its two adjacent electrode units while allowing ionic transfer between those electrode units. The separator may contain cellulose super absorbers to improve filling and act as an electrolyte reservoir to increase cycle life, wherein the separator may be made of a polyabsorb diaper material, for example. The separator may, thereby, release previously absorbed electrolyte when charge is applied to the ESD. In certain embodiments, the separator may be of a lower density and thicker than normal cells so that the inter-electrode spacing (IES) may start higher than normal and be continually reduced to maintain the capacity (or C-rate) of the ESD over its life as well as to extend the life of the ESD.
The separator may be a relatively thin material bonded to the surface of the active material on the electrode units to reduce shorting and improve recombination. This separator material may be sprayed on, coated on, pressed on, or combinations thereof, for example. The separator may have a recombination agent attached thereto, in certain embodiments. This agent may be infused within the structure of the separator (e.g., this may be done by physically trapping the agent in a wet process using a polyvinyl alcohol (PVA or PVOH) to bind the agent to the separator fibers, or the agent may be put therein by electro-deposition), or it may be layered on the surface by vapor deposition, for example. The separator may be made of any suitable material or agent that effectively supports recombination, including, but not limited to, Pb, Ag, any other suitable material, or combinations thereof, for example. While the separator may present a resistance if the substrates of a cell move toward each other, a separator may not be provided in certain embodiments of the invention that may utilize substrates stiff enough not to deflect.
The electrolyte of each electrolyte layer of the ESD of the invention may be formed of any suitable chemical compound that may ionize when dissolved or molten to produce an electrically conductive medium. The electrolyte may be a standard electrolyte of any suitable chemical, including, but not limited to, NiMH, for example. The electrolyte may contain additional chemicals, including, but not limited to, lithium hydroxide (LiOH), sodium hydroxide (NaOH), calcium hydroxide (CaOH), potassium hydroxide (KOH), any other suitable material, or combinations thereof, for example. The electrolyte may also contain additives to improve recombination, such as, but not limited to, Ag(OH)₂, for example. The electrolyte may also contain rubidium hydroxide (RbOH), for example, to improve low temperature performance. In some embodiments of the invention, the electrolyte may be frozen within the separator and then thawed after the ESD is completely assembled. This may allow for particularly viscous electrolytes to be inserted into the electrode unit stack of the ESD before the gaskets have formed substantially fluid tight seals with the electrode units adjacent thereto.
The seals or gaskets of the ESD of the invention (e.g., gaskets 60 a-e) may be formed of any suitable material or combination of materials that may effectively seal an electrolyte within the space defined by the gasket and the electrode units adjacent thereto. In certain embodiments, the gasket may be formed from a solid seal barrier or loop, or multiple loop portions capable of forming a solid seal loop, that may be made of any suitable nonconductive material, including, but not limited to, nylon, polypropylene, cell gard, rubber, PVOH, any other suitable material, or combinations thereof, for example. A gasket formed from a solid seal barrier may contact a portion of an adjacent electrode to create a seal therebetween.
Alternatively, the gasket may be formed from any suitable viscous material or paste, including, but not limited to, epoxy, brea tar, electrolyte (e.g., KOH) impervious glue, compressible adhesives (e.g., two-part polymers, such as Loctite® brand adhesives made available by the Henkel Corporation, that may be formed from silicon, acrylic, and/or fiber reinforced plastics (FRPs) and that may be impervious to electrolytes), any other suitable material, or combinations thereof, for example. A gasket formed from a viscous material may contact a portion of an adjacent electrode to create a seal therebetween. In yet other embodiments, a gasket may be formed by a combination of a solid seal loop and a viscous material, such that the viscous material may improve sealing between the solid seal loop and an adjacent electrode unit. Alternatively or additionally, an electrode unit itself may be treated with viscous material before a solid seal loop, a solid seal loop treated with additional viscous material, an adjacent electrode unit, or an adjacent electrode unit treated with additional viscous material, is sealed thereto, for example.
Moreover, in certain embodiments, a gasket or sealant between adjacent electrode units may be provided with one or more weak points that may allow certain types of fluids (i.e., certain liquids or gasses) to escape therethrough (e.g., if the internal pressures in the cell segment defined by that gasket increases past a certain threshold). Once a certain amount of fluid escapes or the internal pressure decreases, the weak point may reseal. A gasket formed at least partially by certain types of suitable viscous material or paste, such as brai, may be configured or prepared to allow certain fluids to pass therethrough and configured or prepared to prevent other certain fluids to pass therethrough. Such a gasket may prevent any electrolyte from being shared between two cell segments that may cause the voltage and energy of the ESD to fade (i.e., discharge) quickly to zero.
As mentioned above, one benefit of utilizing ESDs designed with sealed cells in a stacked formation (e.g., bi-polar ESD 50) may be an increased discharge rate of the ESD. This increased discharge rate may allow for the use of certain less-corrosive electrolytes (e.g., by removing or reducing the whetting, conductivity enhancing, and/or chemically reactive component or components of the electrolyte) that otherwise might not be feasible in prismatic or wound ESD designs. This leeway that may be provided by the stacked ESD design to use less-corrosive electrolytes may allow for certain epoxies (e.g., J-B Weld epoxy) to be utilized when forming a seal with gaskets that may otherwise be corroded by more-corrosive electrolytes.
The case or wrapper of the ESD of the invention (e.g., case 40) may be formed of any suitable nonconductive material that may seal to the terminal electrode units (e.g., MPUs 12 and 32) for exposing their conductive substrates (e.g., substrates 16 and 36) or their associated leads (i.e., leads 13 and 33). The wrapper may also be formed to create, support, and/or maintain the seals between the gaskets and the electrode units adjacent thereto for isolating the electrolytes within their respective cell segments. The wrapper may create and/or maintain the support required for these seals such that the seals may resist expansion of the ESD as the internal pressures in the cell segments increase. The wrapper may be made of any suitable material, including, but not limited to, nylon, any other polymer or elastic material, including reinforced composites, nitrile rubber, or polysulfone, or shrink wrap material, or any rigid material, such as enamel coated steel or any other metal, or any insulating material, any other suitable material, or combinations thereof, for example. In certain embodiments, the wrapper may be formed by an exoskeleton of tension clips, for example, that may maintain continuous pressure on the seals of the stacked cells. A non-conductive barrier may be provided between the stack and wrapper to prevent the ESD from shorting.
With continued reference to FIG. 3, for example, bi-polar ESD 50 of the invention may include a plurality of cell segments (e.g., cell segments 22 a-e) formed by MPUs 12 and 32, and the stack of one or more BPUs 2 a-d therebetween. In accordance with an embodiment of the invention, the thicknesses and materials of each one of the substrates (e.g., substrates 6 a-d, 16, and 36), the electrode layers (e.g., positive layers 4 a-d and 14, and negative layers 8 a-d and 38), the electrolyte layers (e.g., layers 10 a-e), and the gaskets (e.g., gaskets 60 a-e) may differ from one another, not only from cell segment to cell segment, but also within a particular cell segment. This variation of geometries and chemistries, not only at the stack level, but also at the individual cell level, may create ESDs with various benefits and performance characteristics.
Additionally, the materials and geometries of the substrates, electrode layers, electrolyte layers, and gaskets may vary along the height of the stack from cell segment to cell segment. With further reference to FIG. 3, for example, the electrolyte used in each of the electrolyte layers 10 a-e of ESD 50 may vary based upon how close its respective cell segment 22 a-e is to the middle of the stack of cell segments. For example, innermost cell segment 22 c (i.e., the middle cell segment of the five (5) segments 22 in ESD 50) may include an electrolyte layer (i.e., electrolyte layer 10 c) that is formed of a first electrolyte, while middle cell segments 22 b and 22 d (i.e., the cell segments adjacent the terminal cell segments in ESD 50) may include electrolyte layers (i.e., electrolyte layers 10 b and 10 d, respectively) that are each formed of a second electrolyte, while outermost cell segments 22 a and 22 e (i.e., the outermost cell segments in ESD 50) may include electrolyte layers (i.e., electrolyte layers 10 a and 10 e, respectively) that are each formed of a third electrolyte. By using higher conductivity electrolytes in the internal stacks, the resistance may be lower such that the heat generated may be less. This may provide thermal control to the ESD by design instead of by external cooling techniques.
As another example, the active materials used as electrode layers in each of the cell segments of ESD 50 may also vary based upon how close its respective cell segment 22 a-e is to the middle of the stack of cell segments. For example, innermost cell segment 22 c may include electrode layers (i.e., layers 8 b and 4 c) formed of a first type of active materials having a first temperature and/or rate performance, while middle cell segments 22 b and 22 d may include electrode layers (i.e., layers 8 a/4 b and layers 8 c/4 d) formed of a second type of active materials having a second temperature and/or rate performance, while outermost cell segments 22 a and 22 e may include electrode layers (i.e., layers 38/4 a and layers 8 d/14) formed of a third type of active materials having a third temperature and/or rate performance. As an example, an ESD stack may be thermally managed by constructing the innermost cell segments with electrodes of nickel cadmium, which may better absorb heat, while the outermost cell segments may be provided with electrodes of nickel metal hydride, which may need to be cooler, for example. Alternatively, the chemistries or geometries of the ESD may be asymmetric, where the cell segments at one end of the stack may be made of a first active material and a first height, while the cell segments at the other end of the stack may be of a second active material and a second height.
Moreover, the geometries of each of the cell segments of ESD 50 may also vary along the stack of cell segments. Besides varying the distance between active materials within a particular cell segment, certain cell segments 22 a-e may have a first distance between the active materials of those segments, while other cell segments may have a second distance between the active materials of those segments. In any event, the cell segments or portions thereof having smaller distances between active material electrode layers may have higher power, for example, while the cell segments or portions thereof having larger distances between active material electrode layers may have more room for dendrite growth, longer cycle life, and/or more electrolyte reserve, for example. These portions with larger distances between active material electrode layers may regulate the charge acceptance of the ESD to ensure that the portions with smaller distances between active material electrode layers may charge first, for example.
In an embodiment, the geometries of the electrode layers (e.g., positive layers 4 a-d and 14, and negative layers 8 a-8 d and 38 of FIG. 3) of ESD 50 may vary along the radial length of substrates 6 a-d. With respect to FIG. 3, the electrode layers are of uniform thickness and are symmetric about the electrode shape. In an embodiment, the electrode layers may be non-uniform. For example, the positive active material electrode layer and negative active material electrode layer thicknesses may vary with radial position on the surface of the conductive substrate. Non-uniform electrode layers are discussed in more detail in West et al. U.S. patent application Ser. No. 12/258,854, which is hereby incorporated by reference herein in its entirety.
Although each of the above described and illustrated embodiments of a stacked ESD show a cell segment including a gasket sealed to each of a first and second electrode unit for sealing an electrolyte therein, it should be noted that each electrode unit of a cell segment may be sealed to its own gasket, and the gaskets of two adjacent electrodes may then be sealed to each other for creating the sealed cell segment.
In certain embodiments, a gasket may be injection molded to an electrode unit or another gasket such that they may be fused together to create a seal.
In certain embodiments, a gasket may be ultrasonically welded to an electrode unit or another gasket such that they may together form a seal. In other embodiments, a gasket may be thermally fused to an electrode unit or another gasket, or through heat flow, whereby a gasket or electrode unit may be heated to melt into an other gasket or electrode unit. Moreover, in certain embodiments, instead of or in addition to creating groove shaped portions in surfaces of gaskets and/or electrode units to create a seal, a gasket and/or electrode unit may be perforated or have one or more holes running through one or more portions thereof. Alternatively, a hole or passageway or perforation may be provided through a portion of a gasket such that a portion of an electrode unit (e.g., a substrate) may mold to and through the gasket. In yet other embodiments, holes may be made through both the gasket and electrode unit, such that each of the gasket and electrode unit may mold to and through the other of the gasket and electrode unit, for example.
Although each of the above described and illustrated embodiments of the stacked ESD show an ESD formed by stacking substrates having substantially round cross-sections into a cylindrical ESD, it should be noted that any of a wide variety of shapes may be utilized to form the substrates of the stacked ESD of the invention. For example, the stacked ESD of the invention may be formed by stacking electrode units having substrates with cross-sectional areas that are rectangular, triangular, hexagonal, or any other desired shape or combination thereof.
It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications may be made by those skilled in the art without departing from the scope and spirit of the invention. It will also be understood that various directional and orientational terms such as “horizontal” and “vertical,” “top” and “bottom” and “side,” “length” and “width” and “height” and “thickness,” “inner” and “outer,” “internal” and “external,” and the like are used herein only for convenience, and that no fixed or absolute directional or orientational limitations are intended by the use of these words. For example, the devices of this invention, as well as their individual components, may have any desired orientation. If reoriented, different directional or orientational terms may need to be used in their description, but that will not alter their fundamental nature as within the scope and spirit of this invention. Those skilled in the art will appreciate that the invention may be practiced by other than the described embodiments, which are presented for purposes of illustration rather than of limitation, and the invention is limited only by the claims that follow.

Claims

1. An energy storage device (ESD) comprising:

a first conductive substrate;

a second conductive substrate provided in a stacking direction;

a first active material provided between the first conductive substrate and the second conductive substrate; and

a second active material provided between the first conductive substrate and the second conductive substrate, wherein each of the first and second active materials is folded and comprises:

a plurality of planar sections orthogonal to the stacking direction, wherein each planar section is coupled to an adjoining planar section by a folded section, and wherein each respective planar section of the first active material interfaces with a respective planar section of the second active material.

2. The ESD of claim 1 wherein the first active material is positively charged and the second active material is negatively charged.

3. The ESD of claim 1 wherein the first active material is coupled to the first conductive substrate and the second active material is coupled to the second conductive substrate.

4. The ESD of claim 1 wherein the first active material and the second active material comprise a flexible conductive matrix as the support structure for the respective first and second active materials.

5. The ESD of claim 4 wherein the flexible conductive matrix is nickel-metal foam.

6. The ESD of claim 1 further comprising a first pressure contact to connect the first active material to the first conductive substrate and a second pressure contact to connect the second active material to the second conductive substrate.

7. The ESD of claim 1 wherein at least one of the first active material and the second active material is sleeved within a respective separator prior to being folded.

8. The ESD of claim 1 further comprising:

an electrolyte layer at each interface of the first active material and the second active material, wherein the electrolyte layer comprises a separator and an electrolyte.

9. The ESD of claim 1 further comprising an electrode segment provided at each of the plurality of planar sections for the first and second active materials.

10. The ESD of claim 9 wherein the electrode segment has circular cross-sectional area.

11. The ESD of claim 9 wherein the electrode segment has a rectangular cross-sectional area.

12. The ESD of claim 1 wherein the plurality of planar sections and folded portions for the respective first and second active materials combine to form a respective electronic raceway that serves as an electron transfer path.

13. A method for powder packing electrodes for an energy storage device, the method comprising:

dry packing active powders into a substrate;

wetting the active powders with a wetting agent to ensure an even distribution and surface gradient of the substrate; and

over-coating the active powders with a binder layer on the surface of the substrate.

14. The method of claim 13 wherein the chemical resistance of the binder layer holds the active powders in place while allowing the transportation of electrolyte ions to and from the substrate.

15. The method of claim 13 wherein wetting the dry packed powders allows transport of active materials from the surface of the substrate into the bulk of the substrate.

16. The method of claim 13, further comprising:

dissolving the wetting agent off of the active powders wherein the wetting agent leaves no residuals in the active powders.

17. The method of claim 13, further comprising:

dissolving the wetting agent off of the active powders; and

leaving a residual element in the active powders, wherein the residual element contributes to the electrical properties of the electrode.

18. The method of claim 17 wherein the residual elements increase the capacity of the ESD.

19. The method of claim 13 further comprising providing a common collector and coupling the substrate to the common collector.

20. The method of claim 19 wherein the common collector is folded to form a folded electrode.