HK1170852A - Energy storage devices having mono-polar and bi-polar cells electrically coupled in series and in parallel - Google Patents

Description

Energy storage device with unipolar and bipolar cells electrically coupled in series and in parallel

Cross reference to related patent

The present application claims benefit of U.S. provisional application No.61/172,448 filed 24/4/2009 and U.S. provisional application No.61/224,725 filed 10/7/2009, both of which are incorporated herein by reference in their entirety.

Technical Field

The present invention relates generally to Energy Storage Devices (ESD), and more particularly, to stacked ESD having cells electrically coupled in series, parallel, or both.

Background

Design criteria for an ESD typically include power, energy, and service life, and may also include mass and/or volume limitations. These design factors are often interdependent. For example, increasing the power of the ESD (e.g., by increasing the voltage and/or current capacity) may increase the mass and/or volume of the device.

One approach to increasing the voltage of a bipolar ESD (and thus increasing watt-hours) is to add additional bipolar cells in a higher stack. However, the current capacity of the stack may be substantially the same as the capacity of a single cell. To increase the current capacity of a bipolar ESD, several ESDs are typically wired in parallel. These ESDs each typically have its own pair of end caps for maintaining gas pressure and electrode expansion during cycling, which add weight to the overall system. However, these end caps typically do not add energy or power to the stack. This additional weight is generally referred to as "parasitic" weight because no active material is added as the weight of the individual battery stacks increases.

The above-described techniques unnecessarily limit the increase in power and/or current capacity due to the substantial increase in parasitic weight (and, in some cases, system volume).

Accordingly, it is desirable to provide an ESD with improved performance having cells electrically coupled in series and in parallel.

Disclosure of Invention

In view of the foregoing, the present invention provides apparatus and methods for stacked ESD with cells electrically coupled in series and in parallel.

Any combination of parallel and series configurations may be assembled to produce a particular voltage and current capacity. For example, at least two sub-stacks may be connected in series with a wire to increase the voltage of the total stack. The parasitic weight of such a structure of a bipolar battery may be relatively less than a typical layout (i.e., two or more ESDs electrically coupled in parallel, each ESD having its own respective pair of end caps), because in some embodiments only one pair of end caps may be used.

According to one embodiment, the present invention provides an ESD having a stack of a plurality of electrode units. The stack may include a first sub-stack of the plurality of bipolar electrode units, a second sub-stack of the plurality of bipolar electrode units co-linear with the first sub-stack, and a monopolar type electrode unit located between the first sub-stack and the second sub-stack. The first end cap may be at a first end of the stack of electrode units and the second end cap may be at a second end of the stack of electrode units.

According to one embodiment of the present invention, the present invention provides a stacked ESD having a plurality of electrode units along a stacking axis. The stack may include a monopolar type electrode unit having first and second surfaces on opposite sides thereof, a first bipolar type electrode unit disposed along the stacking axis opposite the first surface, and a second bipolar type electrode unit disposed along the stacking axis opposite the second surface. The first and second bipolar electrode units are electrically coupled in parallel via the monopolar electrode units.

Drawings

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

fig. 1 shows a cross-sectional schematic view of an exemplary structure of a bipolar electrode unit (BPU) according to an embodiment of the invention;

FIG. 2 shows a cross-sectional schematic view of an exemplary structure of the BPU stack of FIG. 1 in accordance with an embodiment of the present invention;

FIG. 3 shows an electrical schematic diagram of an exemplary bipolar ESD with the BPU stack of FIG. 2 in accordance with an embodiment of the present invention;

FIG. 4 shows a cross-sectional schematic view of an exemplary structure of a BPU stack in accordance with an embodiment of the invention;

FIG. 5 shows an electrical schematic diagram of the exemplary bipolar ESD of FIG. 4 in accordance with an embodiment of the present invention;

FIG. 6 shows a perspective view of an exemplary stacked bipolar ESD in accordance with an embodiment of the present invention;

FIG. 7 shows a partial cross-sectional view of the exemplary stacked bipolar ESD of FIG. 6 in accordance with an embodiment of the present invention;

FIG. 8 shows an exploded view of the exemplary stacked bipolar ESD of FIG. 6 in accordance with an embodiment of the present invention; and

fig. 9 shows an exploded view of the exemplary stacked bipolar ESD of fig. 6 in accordance with an embodiment of the present invention.

Detailed Description

The present invention provides apparatus and methods for stacked Energy Storage Devices (ESD), and are described below with reference to fig. 1-9. The present invention relates to ESD such as batteries, capacitors, and any other electrochemical energy or power storage device that can store and/or provide electrical energy or current. It should be understood that although the present invention is described with respect to stacked bipolar ESDs electrically coupled in series and in parallel, the concepts discussed are applicable to any inter-cell electrode structure, including but not limited to parallel plate, prismatic, folded, coiled, and/or bipolar structures, as well as other suitable structures, or any combination of these structures.

An ESD with a sealed cell in a stacked form may include a series of stacked bipolar electrode units (BPUs). These BPUs are each provided with a positive active material electrode layer and a negative active material electrode layer covering opposite faces of a current collector. Any two BPUs may be stacked on each other with an electrolyte layer provided between the positive electrode active material electrode layer of one BPU and the negative electrode active material electrode layer of the other BPU for electrically isolating the current collectors of the two BPUs. The current collectors of any two adjacent BPUs, along with the two active material electrode layers and the electrolyte therebetween, are sealed single cells or cell segments. An ESD comprising a stack of such cells, each cell having a portion of a first BPU and a portion of a second BPU, shall be referred to herein as a "stacked bipolar" ESD.

The ESD may include a plurality of batteries that may be electrically coupled in series, parallel, or both. Bipolar ESD can eliminate the interconnected current-carrying components present in ESD that simply connect individual cells together in series. For example, the reduction of bipolar ESD connection materials (and thus parasitic weight) may reduce resistance and increase power, and may make the ESD relatively smaller and lighter.

Fig. 1 shows an illustrative "flat-panel" bipolar electrode unit BPU 102 according to an embodiment of the invention. The flat plate structure for stacked cell ESD has been discussed in detail in U.S. patent application No.11/417,489 to Ogg et al and U.S. patent application No.12/069,793 to Ogg et al, both of which are incorporated herein by reference in their entirety. The BPU 102 may include a positive active material electrode layer 104 disposed on an impermeable conductive substrate or current collector 106, and a negative active material electrode layer 108 that may be disposed on the other side of the impermeable conductive substrate or current collector 106.

It should be appreciated that the bipolar electrode may have any suitable shape or geometry. For example, in some embodiments of the invention, a "flat-panel" BPU may be replaced or supplemented with a "disk-shaped" electrode. The disk shaped electrode can reduce stress generated during bipolar ESD operation. Disc-shaped and pressure-equalized electrodes have been discussed in detail in U.S. patent application No.12/258,854 to West et al, which is incorporated herein by reference in its entirety.

For example, as shown in fig. 2, a plurality of BPUs 202 may be substantially vertically stacked into a stack 220, with an electrolyte layer 210 that may be disposed between two adjacent BPUs 202, such that the positive electrode layer 204 of one BPU202 is opposite the negative electrode layer 208 of an adjacent BPU202 via the electrolyte layer 210. Each electrolyte layer 210 may include a separator (not shown) that may hold an electrolyte therein. The separator may electrically isolate the positive electrode layer 204 from the adjacent negative electrode layer 208 while allowing ion migration between the electrode units.

With continued reference to the stacked state of the BPUs 202 in fig. 2, for example, the assembly of the positive electrode layer 204 and the substrate 206 contained in a first BPU202, the negative electrode layer 208 and the substrate 206 of a second BPU202 adjacent to the first BPU202, and the electrolyte layer 210 located between the first and second BPUs 202 is 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 segments 222.

Fig. 3 shows a circuit schematic of the stack 220 of fig. 2 according to an embodiment of the invention. As shown in fig. 3, a bipolar ESD may include one or more BPUs 202 stacked and connected in series to provide a desired voltage.

Fig. 4 shows a schematic cross-sectional view of a BPU stack structure according to an embodiment of the invention. As shown in fig. 4, for example, individual battery stacks or sub-stacks 421a and 421b may be configured to be electrically coupled in parallel by having "sub-terminal" monopolar type electrode units located between the sub-stacks (see, e.g., sub-terminal MPU 401). A positive or negative sub-terminal unipolar electrode unit (MPU) may be located between individual cell stacks or sub-stacks within a bipolar ESD. The sub-terminal MPU may have an active material electrode layer having the same polarity (i.e., positive or negative) as that provided on the opposite side of the substrate or current collector. For the sub-terminal MPU, any suitable active material may be used, and in some embodiments, the active material electrode layers on either side of the sub-terminal MPU may be substantially the same active material or may be different active materials with the same polarity.

For example, FIG. 4 shows a sub-terminal MPU401 located within a stack 420 of a bipolar ESD 450. The sub-terminal MPU401 may include a negative electrode active material electrode layer 405a that may be disposed on a first side of an impermeable conductive substrate or current collector 409, and a negative electrode active material electrode layer 405b that may be disposed on the other side of the impermeable conductive substrate 409. The sub-terminal MPU401 may be configured to electrically couple the cell segments of sub-stack 421a (see, e.g., cell segments 422a-422c) in parallel with the cell segments of sub-stack 421b (see, e.g., cell segments 422d-422 f). For example, the sub-terminal MPU401 may be provided with a tab (tab) or a flange 407. In some embodiments, for example, the flange 407 may provide electrical connection to a bipolar electrode unit or a monopolar type unit corresponding to the respective substrate to which the flange 407 is attached. For example, as shown in fig. 4, the flange 407 is attached to the substrate 409 of the sub-terminal MPU 401. However, it should be understood that the tabs or flanges may be provided to the substrate of any suitable electrode unit of the present invention, including, for example, BPUs, sub-terminal MPUs, and terminal MPUs (see, e.g., flange 607 in fig. 6-9).

The sub-terminal MPU401 may act as an electrical isolation layer, a mechanical barrier, or both between the sub-stacks. In some embodiments, the sub-terminal MPU401 may have a different geometry than the bipolar electrode unit (see, e.g., BPUs 402 a-d). For example, the substrate 409 of the sub-terminal MPU401 may be relatively thicker or relatively thinner than the substrate 406a of the BPU 402 a. For example, substrate 409 may have a variable thickness relative to substrate 406a because electrodes with the same polarity (e.g., electrode layers 405a and 405b) on both sides of substrate 409 may expand and/or contract differently than electrodes with opposite polarities (e.g., electrode layers 408a and 404a) on both sides of substrate 406 a. For example, if the MPU401 has positive electrode layers on both sides of the substrate 409, one or both positive electrode layers may compress the substrate 409. Further, in some embodiments, the sub-stacks of the ESD may have different basic cells and/or different chemical compositions (e.g., sub-stack 421a may have a chemical composition of nickel metal hydride ESD, while sub-stack 421a may use a capacitor). For example, in such embodiments, the sub-stacks may not expand and/or contract as much as each other, thereby exerting a net force (net force) on the MPU 401. Thus, in some embodiments, the substrate 409 may be designed to be relatively thicker and more robust than the substrates 406 a-d. However, it should be understood that in some embodiments, the substrate 409 of the sub-terminal MPU401 may be substantially the same as the substrate of the BPU (see, e.g., substrates 406a-d of BPUs 402 a-d).

The sub-terminal MPU401 may have any suitable inter-electrode spacing between the active materials of adjacent cell segments therein, and may have any suitable pad configuration. The inter-electrode spacing may depend on various ESD applications. For example, for relatively low leakage/high energy batteries, it may be desirable to pack a relatively large amount of active material and/or have a relatively thick electrode base material to withstand increased loads. For relatively high power applications, it may be preferable to pack less material and/or close under relatively high forces in order to reduce the spacing between the electrodes.

There may be many standards for ESD design. These standards typically specify power, energy, and service life, and may have mass and/or volume limitations. These criteria may not be met by one ESD type alone. Thus, in some embodiments, it may be preferable to combine ESD of the energy storage type to meet design requirements. The bipolar ESD of the present invention can be configured to accommodate a variety of ESD types to meet design requirements. For example, as discussed previously, one sub-stack may have the chemical composition of a nickel metal hydride ESD, while another sub-stack may use a capacitor.

The bipolar ESD450 may include one or more basic cells. For example, a suitable electrochemical ESD chemical composition may include a metal hydride, lithium, or any other suitable chemical composition, or a combination thereof, and the base unit may include an electrostatic capacitor. Such multi-cell ESD can be configured as series or parallel power distributions, or both, and the device can include multiple types. In some embodiments, the individual sub-stacks in the ESD may have different chemical compositions. For example, sub-stack 421a may include a metal hydride composition, while sub-stack 421b may include a lithium ion composition. In some embodiments, cells within the same sub-stack may have different chemical compositions from each other, even within the same cell.

As described above, in some embodiments, the ESD may include one or more sub-stacks having capacitors stacked therein. The capacitor may include an electrochemical double layer. The bilayer component may refer to the accumulation of ions and electrons on the surface of the electrode material (e.g., they may be dependent on the contact surface area). The effect can be relatively more electrostatic than electrochemical in that both ions and electrons can be coupled on the surface of the electrode material. This may be similar to an electrostatic capacitor, for example. The positive and negative electrode layers of the capacitor may have substantially the same composition, such that there may be no or substantially no "natural" electrochemical potential when the ESD is assembled. When the ESD is charged, the potential can rise, for example, by having electrons accumulate substantially equal amounts of positive ionic charge on one face and on the same surface. A similar situation occurs on the negative electrode, for example, where negative ions accumulate at the electrode surface due to electron depletion (e.g., "holes") on the electron depleted surface of the negative electrode. It should be understood that either side of the capacitor may be positive or negative, as described above in connection with the bipolar cell of the present invention.

When the capacitor is electrically coupled in parallel with the ESD, the entire composite device can have a relatively high operating voltage. For example, metal hydride ESD can be aqueous and can have an operating range of 1.4 volts. Capacitors with electrochemical double layers can be formed from any suitable electrolyte and can have an operating range, for example, from 1.25 volts or less to 20 volts or more. These capacitors may also have relatively low internal resistance and may support ESD with relatively high current consumption. For example, for high rate pulses, these capacitors may accept most of the current drain before ESD, which may buffer the ESD and may increase the cycle life of the ESD.

Other capacitors may be free of double layers of ions and electrons. Rather, they can only work by electrostatic coupling caused by the accumulation and depletion of electrons from the surface of a conductor (e.g., a metal foil). Once charged, these electrons cannot propagate through the dielectric isolation layer, but need to be in close proximity to maintain electrostatic coupling. Once the positive and negative terminals are coupled to complete the circuit, electrons can flow back through the wire to rebalance to substantially zero voltage. The capacity of these capacitors can be relatively lower than capacitors with electrochemical double layers.

The number of capacitor cells stacked on the sub-stack may be determined according to the voltage limit of the ESD. In some embodiments, the voltage of the capacitor sub-stack may be equal to or greater than the voltage of the ESD. Further, in some embodiments, for example, the voltage limit of each capacitor cell may depend on the breakdown voltage of the electrolyte solvent. For liquid-based solvent devices, exemplary voltage limits may be from 1.2 volts (e.g., aqueous) to 20 volts (e.g., organic and silicone). In some embodiments, the ESD of the present invention may incorporate a capacitor into a sub-stack having substantially the same solvent as used for another sub-stack having, for example, a metal hydride chemistry, in which the battery may be configured to have a voltage limit of 1.5 volts.

With continued reference to fig. 4, where there are two separate three-cell stacks (i.e., sub-stacks 421a and 421b), the sub-terminal MPU401 is then centrally located in the stack 420 between sub-stacks 421a and 421 b. However, it should be understood that the sub-terminal MPU401 may be disposed at any suitable location within the stack 420. For example, an individual battery stack (see, e.g., sub-stack 421a) may have any suitable number of cells (e.g., to increase the voltage of a particular stack or sub-stack), such that sub-terminal MPU401 may be located at any suitable location between individual sub-stacks in the stack (e.g., sub-stacks 421a and 421 b). It should also be understood that ESD450 may have any suitable number of individual battery stacks or sub-stacks with an appropriate number of sub-terminal MPUs disposed therebetween. For example, in some embodiments, multiple sub-stacks may be combined to increase the voltage and/or current capacity of the ESD.

As shown in fig. 4, for example, according to one embodiment of the invention, a positive or negative terminal, or terminal unipolar cell (MPU), may be provided along with a stack 420 of one or more BPUs 402a-d and a sub-terminal MPU401 to form a stacked bipolar ESD 450. In the configuration shown in fig. 4, for example, the polarity of the terminal MPU may be opposite to that of the sub-terminal MPU 401. The positive electrode terminal MPU 421b, which includes the positive electrode active material electrode layer 414b on one side of the impermeable conductive substrate 416b thereof, may be located at the first end of the stack 420 provided with the electrolyte layer (i.e., the electrolyte layer 410f), so that the positive electrode layer 414b of the positive electrode terminal MPU412b may be opposed to the negative electrode layer (i.e., the layer 408d) of the BPU (i.e., the BPU 402d) at the first end of the stack 420 via the electrolyte layer 410 f. The positive electrode terminal MPU412a, which includes a positive electrode active material electrode layer 414a on one side of its impermeable conductive substrate 416a, may be located at the second end of the stack 420 where the electrolyte layer (i.e., electrolyte layer 410a) is disposed, so that the positive electrode layer 414a of the positive electrode terminal MPU412a may be opposed to the negative electrode layer (i.e., layer 408a) of the BPU (i.e., BPU 402a) at the second end of the stack 420 via the electrolyte layer 410 a. The terminal MPUs 412a and 412b may be provided with corresponding positive electrode leads 413a and 413b, respectively.

For example, the substrate and electrode layers of each terminal MPU or sub-terminal MPU may form a cell segment having a substrate, and electrode layers of its adjacent BPUs, and an electrolyte layer therebetween, as shown in fig. 4 (see, for example, cell segments 422a/422f and cell segments 422c/422 d). The number of stacked BPUs in stack 420 may be one or more and may be appropriately determined to meet the desired voltage of ESD 450. The number of stacked BPUs in a sub-stack (e.g., sub-stacks 421a and 421b) may be one or more and may be appropriately determined to meet a desired voltage of ESD450, for example. Each BPU may provide any desired potential, and thus the desired voltage of the ESD450 may be achieved by effectively increasing the potential provided by each BPU component. It should be understood that each BPU need not provide an equal potential.

In one suitable embodiment, the bipolar ESD450 may be configured such that the BPU stack 420 and its respective positive terminal MPUs 412a and 412b may be at least partially encapsulated (e.g., hermetically sealed) under reduced pressure into an ESD casing or package 440. The terminal MPU conductive substrates 416a and 416b (or at least their respective electrode leads 413a and 413b) may be routed from the ESD casing or package 440, for example, to mitigate external influences during use and prevent environmental degradation.

To prevent the electrolyte of a first cell segment (see, e.g., electrolyte layer 410a of cell segment 422 a) from bonding with another cell segment (see, e.g., electrolyte layer 410b of cell segment 422b), a gasket or sealant may be laminated with the electrolyte layer between adjacent electrode units to seal the electrolyte within its particular cell segment. The gasket or sealant can be any suitable compressible or incompressible solid or viscous substance, any other suitable substance, or combination thereof, which can be disposed, for example, for adjacent electrode units of a particular battery to seal the electrolyte therebetween. In one suitable configuration, such as shown in fig. 4, the bipolar ESD of the present invention may include gaskets or seals 460a-f disposed as baffles around the electrolyte layers 410a-f and active material electrode layers 404a-d/414a-b and 408a-d/405a-b of each of the battery segments 422 a-e. The gasket or sealant can be continuous and hermetic and can seal the electrolyte between the gasket and the adjacent electrode units of the cell (i.e., those or that BPU and sub-terminal MPU/terminal MPU adjacent to the gasket or seal). For example, the gasket or sealant may provide appropriate spacing between adjacent electrode units of the battery. In some embodiments, a dynamic flexible seal or gasket may be provided. In the present application, the gasket may be mechanically sized while maintaining substantial sealing contact with the abutment surface. For example, the dynamic flexible seal or gasket may be configured to deform in one preferred direction or more preferred directions. Dynamic flexible seals or gaskets have been discussed in detail in U.S. patent application No.12/694,638 to West et al, which is incorporated herein by reference in its entirety.

When the cell segments of the stacked bipolar ESD450 are sealed to prevent the electrolyte of a first cell segment (see, e.g., electrolyte layer 410a of cell segment 422 a) from bonding with the electrolyte of another cell segment (see, e.g., electrolyte layer 410b of cell segment 422b), the cell segments can create a pressure differential between adjacent cells (e.g., cells 422a/422b) as the cells are charged and discharged. A balancing valve may be provided to reduce the pressure differential created thereby. The balancing valve acts mechanically or chemically as a semipermeable membrane or rupture disk to allow the transfer of gas and substantially prevent the transfer of electrolyte. The ESD may include a BPU, sub-terminal MPU, and terminal MPU with any combination of balanced valves. Pressure equalization valves have been discussed in detail in U.S. patent application No.12/258,854 to West et al, which is hereby incorporated by reference in its entirety.

Fig. 5 shows an electrical schematic diagram of the bipolar ESD of fig. 4 in accordance with an embodiment of the invention. For example, the cell segments within each respective individual cell stack or sub-stack may be electrically coupled in series with other cells in the sub-stack (see, e.g., the series arrangement of fig. 2 and 3). Then, the two sub-stacks may be electrically coupled in parallel to each other via the sub-terminal MPU (see, for example, the sub-terminal MPU401 in fig. 4). Such a configuration may allow, for example, multiple cells to be electrically coupled in series and/or parallel in a stack, with only a pair of end caps (see, e.g., end caps 618 and 634 in fig. 6-8). This may reduce the parasitic weight of the ESD as compared to an ESD that uses multiple end caps and is electrically coupled in series and in parallel.

As shown in fig. 5, these sub-stacks may be electrically coupled in parallel via one or more wires that may be attached to the sub-terminal MPU 401. These wires may be attached to one or more flanges (see, e.g., flange 407 in fig. 4 and flange 607 in fig. 6-9) on the sub-terminal MPU401 substrate. It should be understood that the use of wires is only one of many suitable methods for parallel connection. For example, in some embodiments, the sub-terminal MPU may be directly bonded to a conductive external container (see, e.g., ESD package 440 in FIG. 4) without the need for wires. In this embodiment, for example, each end of the ESD may have both a positive post or electrode lead (see, e.g., leads 413a and 413b) and a negative housing (not shown) in contact with a conductive outer container for providing a negative electrical connection. Any other suitable method of electrically coupling the sub-stacks in parallel via the sub-terminal MPUs 401 or any combination of these methods may be used. For example, in some embodiments, both methods of wire and sub-terminal MPU bonding directly to a conductive external container may be used.

Fig. 6 and 7 show a perspective view and a partial cross-sectional view, respectively, of a stacked bipolar ESD in accordance with an embodiment of the invention. Stacked bipolar ESD 650 may include compression bolt 623, alignment collars 624a and 624b, mechanical springs 626a and 626b, stack 620 (including substrate flange 607), and rigid end caps 634 and 618 disposed at each end of stack 620. The straightening ring can be disposed at either end of the stacked bipolar ESD 650. For example, a alignment collar 624a and a alignment collar 624b may be disposed on opposite ends of the ESD 650. Mechanical springs may be disposed between the alignment rings 624a/624b and the rigid end cap 634/618. For example, a mechanical spring 626a may be disposed between the straightening ring 624a and the rigid end cap 634, and a mechanical spring 626b may be disposed between the straightening ring 624b and the rigid end cap 618. The mechanical springs 626a and 626b may be configured to flex in response to forces generated during operation and cycling of the ESD 650. In some embodiments, the amount of deflection of springs 626a and 626b may be proportional to the applied load.

Rigid end caps 634 and 618 may be substantially shaped to conform to the electrodes and/or substrate (see, e.g., BPUs 402a-d in fig. 4) of bipolar ESD 650. For example, end caps 634 and 618 may conform to a "flat plate," "disk," any other shape, or combination of shapes, that the electrodes and/or substrates of ESD 350 have.

In some embodiments, substrate flange 607 may be disposed about ESD 650 and may extend radially outward from stack 620. The flange 607 may provide, for example, an electrical connection to a bipolar electrode unit or a monopolar type unit corresponding to a respective impermeable conductive substrate to which the flange 607 is attached (see, for example, flange 407 of the neutron terminal MPU401 in fig. 4). Although flange 607 in fig. 6 is shaped as a "tongue depressor," it may be any other suitable shape and any other suitable size and configured to extend radially outward from stack 620. For example, the cross-sectional area of the flange 607 may be substantially rectangular, triangular, circular or elliptical, hexagonal, or any other desired shape or combination of shapes, and may be configured to electrically couple with a particular connector or connectors.

Fig. 8 and 9 show exploded views of the stacked bipolar ESD of fig. 6 in accordance with one embodiment of the present invention. As shown in fig. 8, for example, the stack 620 may include sub-stacks 621a and 621 b. The sub-stack 621a may include a stack of 5 BPUs 602 a. Similarly, sub-stack 621b may comprise a stack of 5 BPUs 602 b. However, it should be understood that any suitable number of battery segments and/or bipolar cells may be provided in the sub-stacks 621a and 621b to meet a desired voltage and/or current capacity of the ESD 650. The sub-terminal MPU 601 may be disposed between the sub-stacks 621a and 621b to separate the BPU series electrical connection of sub-stack 621a from the BPU series electrical connection of sub-stack 621 b. The sub-terminal MPU 601 may be configured to couple the BPUs of sub-stack 621a in parallel with the BPUs of sub-stack 621b, e.g., via a plurality of flanges 607 (see, e.g., flanges 607 in fig. 9) attached to respective substrates. As described above in connection with fig. 5, it should be understood that the use of flanges (e.g., flange 607) is but one of many suitable methods for forming parallel connections between ESD sub-stacks.

Referring to fig. 9 (representing region 690 in fig. 8), the sub-terminal MPU 601 may have active material electrode layers of the same polarity (i.e., positive or negative) as provided on the opposite side of the substrate or current collector. As shown in fig. 9, for example, the sub-terminal MPU 601 may include a positive electrode active material electrode layer 603 disposed on a first face of an impermeable conductive substrate or current collector 609. A second positive electrode active material electrode layer may be disposed on the other side (not shown) of the impermeable conductive substrate 609.

The BPU 602a may include a positive active material electrode layer 604 that may be disposed on a first side of an impermeable conductive substrate or current collector 606, and a negative active material electrode layer 608 (not shown) that may be disposed on the other side of the impermeable conductive substrate 606. The BPU 602b may include a negative active material electrode layer 608 that may be disposed on a first side of an impermeable conductive substrate or current collector 606, and a positive active material electrode layer 604 (not shown) that may be disposed on the other side of the impermeable conductive substrate 606. The substrate 606 may further include a substrate flange 607 extending radially outward therefrom.

By separating the sub-stacks of ESD 650, the sub-terminal MPU 601 can actually act as an end cap for a particular sub-stack. As shown in fig. 6-8, for example, ESD 650 has at least two sub-stacks electrically coupled in parallel and arranged in a single stack 620 having only a pair of end caps 618 and 634.

With continued reference to fig. 9, hard stops 662 may be provided between each respective electrode unit (e.g., between the BPUs 602a, 602b and the sub-terminal MPU 601). The hard stop 662 may substantially surround the contents of each respective battery segment. In addition, each hard stop 662 may have a support upon which a substrate (e.g., substrates 606 and 609) may be securely positioned.

A set of bolt holes 664 may be provided along the outer rim of the hard stop 662 that mate with compression bolts (see, e.g., compression bolts 623 in fig. 6) or any other suitable rigid fastener. For example, during assembly, the bolt holes 664 may align the entire stack of electrode units (see, e.g., BPUs 402a-d, sub-terminal MPU401, and terminal MPUs 412a and 412b), and may provide stability during operation. The bolt holes 664 should be sized to fit a particular bolt or any other suitable rigid fastener. Although the bolt holes 664 are shown as circular, they may also be substantially rectangular, triangular, oval, hexagonal, or any other desired shape or combination of shapes.

The hard stop 662 may also include a plurality of substrate supports 674 that may be aligned with the substrate flange 607. The substrate support 674 can have a flange extending radially outward from the stack 620 through the hard stop 662 to allow the flange to be electrically coupled to leads, for example. Although the hard stops 662 are shown as having 5 substrate supports 674 each, any suitable number of supports 674 may be provided, and this number depends on the particular electrode unit used for ESD. In addition, the hard stops 662 may be configured to substantially set the inter-electrode spacing of the ESD. Various techniques for adjusting the inter-electrode spacing of an ESD have been discussed in detail in U.S. patent application No.12/694,638 to West et al, which is incorporated herein by reference in its entirety.

The substrates used to form the electrode units of the present invention (e.g., substrates 406a-d, 409, 416a and 416b) may be formed of any suitable material that is electrically conductive and impermeable or substantially impermeable, including, but not limited to, for example, non-porous metal foils, aluminum foils, stainless steel foils, cover materials containing nickel and aluminum, cover materials containing copper and aluminum, nickel plated steel, nickel plated copper, nickel plated aluminum, gold, silver, any other suitable material, or combinations of such materials. In some embodiments, each substrate is composed of two or more pieces of metal foil attached to each other. For example, the substrate of each BPU may be typically 0.025 mm to 5 mm thick, while the substrate of each MPU may be 0.025 mm to 10 mm thick and serve as a terminal or sub-terminal for ESD. For example, the metallized foam may be incorporated into a planar metal film or foil with any suitable substrate material, and thus the electrical resistance between the active materials of the cell segments may be reduced by extending such conductive composite material throughout the electrodes.

In some embodiments, the substrate 409 of the sub-terminal MPU401 may be formed of any insulating and impermeable or substantially impermeable substance including, but not limited to, various plastics, phenolics, ceramics, binary composite epoxy preforms, glass ceramics, multi-dimensional woven fiber composites, any other suitable material, or combinations of these materials, for example.

The positive electrode layers (e.g., positive electrode layers 404a-d, 414a, and 414b) provided on these substrates to form the electrode unit of the present invention may be formed of any of various combinationsSuitable active materials include, but are not limited to, nickel hydroxide (Ni (OH))₂) Zinc (Zn), any other suitable material or combination of materials. The positive electrode active material may be sintered and impregnated, water-borne binder coated and pressed, organic binder coated and pressed, or contained by any other suitable technique for containing the positive electrode active material and other supporting chemicals in a conductive matrix. The positive electrode layer of the electrode unit may have particles including, but not limited to, for example, Metal Hydride (MH), palladium (Pd), silver (Ag), any other suitable material, or a combination of these materials, which are impregnated into its matrix to reduce the degree of swelling. This can increase cycle life, improve recombination effects, and reduce pressure within the battery segment. These particles, such as MH, may also incorporate active material slurries, such as Ni (OH)₂So as to improve the conductivity inside the electrode and assist recombination.

The negative electrode layers provided on these substrates to form the electrode units of the present invention (e.g., negative electrode layers 408a-d, 405a, and 405b) may be formed from any suitable active material, including, but not limited to, for example, MH, Cd, Mn, Ag, any other suitable material, or combinations of such materials. 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 and other supporting chemicals in a conductive matrix. The negative electrode side may include chemical materials including, but not limited to, for example, Ni, Zn, Al, any other suitable material, or combinations of these materials, which are impregnated into the matrix of the negative electrode material to stabilize the structure, mitigate oxidation, and extend cycle life.

Various suitable binders may be mixed with the active material layers to retain the layers on their substrates, including, but not limited to, for example, organic carboxymethylcellulose (CMC) binder, Creyton rubber, PTFE (polytetrafluoroethylene), any other suitable material, or a combination of these materials. An ultra-static (still) adhesive, such as 200ppi metal foam, may also be used in the laminate ESD construction of the present invention.

The separator of each electrolyte layer in the ESD of the present invention may be formed of any suitable material that electrically isolates its two adjacent electrode cells while allowing the transfer of ions between those electrode cells. For example, the separator may comprise a cellulosic superabsorbent material to increase packing and act as an electrolyte reservoir to increase cycle life, wherein the separator may be formed from a polymeric absorbent fabric material. Thus, when the ESD is charging, the separator can release the previously absorbed electrolyte. In some embodiments, the density and thickness of the separator may be lower than conventional batteries, so the inter-electrode spacing (IES) may be initially higher than normal and then decrease, thus both maintaining capacity (or charge rate) over the life of the ESD and extending the life of the ESD.

The separator may be a relatively thin material that adheres to the surface of the active material on the electrode unit to reduce short circuits and improve recombination. For example, the separator material may be sprayed, painted, pressed, or a combination of these operations. In some embodiments, the separator may have a complexing agent (complexing agent) attached thereto. For example, such a composite can be impregnated into the structure of the separator (this can be achieved, for example, by wet physical entrapment of the composite using polyvinyl alcohol (PVA or PVOH) to bind it to the separator fibers, or by placing the composite there by electrodeposition), or it can be laminated to the surface using vapor deposition. The separator may be formed of any suitable substance or chemical effective to support the recombination including, but not limited to, for example, Pb, Ag, any other suitable material, or a combination of such materials. While the spacers may present resistance as the substrates of the cells move toward each other, some embodiments of the invention may not provide spacers, which may utilize substrates that are sufficiently rigid to not bend.

The electrolyte of each electrolyte layer in the ESD of the invention may be formed from any suitable compound, which may beTo ionize upon dissolution or melting to produce a conductive medium. The electrolyte may be a standard electrolyte of any suitable chemistry including, but not limited to, NiMH, for example. The electrolyte may contain additional chemical materials including, but not limited to, for example, lithium hydroxide (LiOH), sodium hydroxide (NaOH), calcium hydroxide (CaOH), potassium hydroxide (KOH), any other suitable material, or a combination of these materials. The electrolyte may also contain additives to enhance complexing, including but not limited to, for example, Ag (OH)₂. The electrolyte may also contain, for example, rubidium hydroxide (RbOH) 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 fully assembled. This allows a particularly viscous electrolyte to be inserted into the stack of electrode cells of the ESD prior to the gasket actually forming a substantial fluid seal with its adjacent electrode cell.

The ESD seals or gaskets of the present invention (e.g., gaskets 460a-f) may be formed of any suitable material or combination of materials that effectively seals the electrolyte to the space defined by the gasket and the electrode units adjacent thereto. In some embodiments, the gasket may be made of a solid sealing flap, a solid seal ring, or a plurality of ring members capable of forming a solid seal ring, which may be composed of any suitable electrically non-conductive material, including, but not limited to, nylon, polypropylene, battery protection material (cell gard), rubber, PVOH, any other suitable material, or combinations of these materials, for example. A gasket made of a solid sealing flap may contact a portion of an adjacent electrode to form a seal therebetween.

Alternatively or additionally, the liner may be made of any suitable adhesive material or slurry, including, but not limited to, epoxy, asphalt tar (break tar), electrolyte (e.g., KOH) bleed-through glue, compressible adhesive (e.g., two-part polymer such as Loctite manufactured by Henkel corporationBrands binders made of, for example, silicon,Acrylic and/or Fiber Reinforced Plastic (FRP) and is resistant to penetration by electrolytes), any other suitable material, or combinations of these materials. A gasket made of an adhesive material may contact a portion of an adjacent electrode to form a seal therebetween. In some embodiments, the gasket may be formed of a combination of a solid seal ring and an adhesive material, such that the adhesive material may improve the sealing condition between the solid seal ring and the adjacent electrode unit. Alternatively or additionally, for example, the electrode unit itself may be treated with a viscous material and then the solid seal ring sealed, a solid seal ring treated with another viscous material, an adjacent electrode unit, or an adjacent electrode unit treated with another viscous material.

Also, in some embodiments, the gasket or sealant located between adjacent electrode units may provide one or more weak points that may allow some type of fluid (i.e., some liquid or gas) to escape therefrom (e.g., when the increase in pressure within the cell segment defined by the gasket exceeds a certain threshold). Once a certain amount of fluid escapes or the internal pressure decreases, the weak point reseals. A pad formed at least in part from some type of suitable viscous material or slurry, such as a fabric (brail), may be configured or prepared to allow some type of fluid to pass therethrough, and configured or prepared to prevent other types of fluid from passing therethrough. Such a gasket may prevent any electrolyte from being shared by the two battery segments, which could cause the ESD voltage and energy to rapidly decay (i.e., discharge) to zero.

As previously discussed, there is an advantage to utilizing such an ESD (e.g., bipolar ESD 450) in which the sealed cell is designed in a stacked configuration, i.e., the discharge rate of the ESD can be increased. This increase in discharge rate may allow the use of some less corrosive electrolytes (e.g., by eliminating or reducing irritancy, enhancing conductivity, and/or chemically reacting one or more components in the electrolyte) that is not feasible in prismatic or coiled ESD designs. This latitude in using a less corrosive electrolyte provided by the stacked ESD design allows the use of some epoxies (e.g., J-B Weld epoxy) in forming the seal with the gasket, which can be corroded by the more corrosive electrolyte.

The hard stops of the ESD of the present invention (see, e.g., hard stop 662 in fig. 9) may be formed from any suitable material including, but not limited to, various polymers (e.g., polyethylene, polypropylene), ceramics (e.g., alumina, silica), any other suitable material that is mechanically durable and/or chemically inert, or combinations of such materials. The hard stop material may be selected, for example, to withstand the various chemicals used in ESD.

The mechanical springs of the present invention (see, e.g., mechanical springs 626a and 626b in fig. 6-8) may be any suitable spring that can bend or deform in response to an applied load. For example, the mechanical spring may be designed to bend in response to a particular load or a particular load threshold. Any suitable type of spring may be used, including compression springs (e.g., open coil springs, unequal pitch springs, and torsion springs), leaf springs, any other suitable spring, or a combination of springs. The spring itself may be any suitable material including, but not limited to, high carbon steel, alloy steel, stainless steel, copper alloy, any other suitable non-flexible or flexible material, or a combination of these materials.

The end caps of the present invention (see, e.g., end caps 618 and 636 of fig. 6-8) may be formed from any suitable material or combination of materials that are electrically conductive or insulative, including, but not limited to, various metals (e.g., steel, aluminum, and copper alloys), polymers, ceramics, any other suitable material that is electrically conductive or insulative, or a combination of such materials.

A housing or package for an ESD of the present invention (see, e.g., package 440 in fig. 4) may be provided and may be composed of any suitable insulating material that can be sealed to the terminal electrode units (e.g., terminal MPUs 412a and 412b) to expose their conductive substrates (e.g., substrates 416a and 416b) or their associated leads (e.g., leads 413a and 413 b). The package may also be configured to create, support, and/or maintain a seal between the gasket and its adjacent electrode units to isolate the electrolyte within their respective cell segments. The packaging can create and/or maintain the support required for these seals so that the seals can resist expansion of ESD as the internal pressure of the cell segments increases. The packaging may be composed of any suitable material including, but not limited to, nylon, any other polymeric or elastomeric material (including reinforced composites, nitrile rubber or polysulfone), shrink wrap materials, any rigid material (such as enameled steel or any other metal), any insulating material, any other suitable material, or combinations of these materials, for example. In some embodiments, the package may be formed by the exoskeleton of the tension clamp, for example, which may maintain continuous pressure on the stacked cells. A non-conductive barrier may be provided between the laminate and the package to prevent ESD short circuits.

With continued reference to fig. 4, for example, the bipolar ESD450 of the present invention may include a plurality of battery segments (e.g., battery segments 422a-f) comprised of terminal MPUs 412a and 412b, and a sub-stack of one or more BPUs 402a-d with sub-terminal MPUs 401 between the sub-stacks. According to one embodiment of the invention, the thickness and material of each of the substrates (e.g., substrates 406a-d, 409, 416a, and 416b), electrode layers (e.g., positive electrode layers 404a-d, 414a, and 414b, and negative electrode layers 408a-d, 405a, and 405b), electrolyte layers (e.g., layers 410a-f), and gaskets (e.g., gaskets 460a-f) may be different from one another, not only between different cell segments, but also within a particular cell segment. Varying the geometry and chemistry, not only at the stack level, but also at the individual cell level, can produce ESD with different advantages and operating characteristics.

Furthermore, the materials and geometries of the substrate, electrode layers, electrolyte layers, and gaskets may vary from cell segment to cell segment along the height of the stack. With further reference to fig. 4, for example, the electrolyte used in each of the electrolyte layers 410a-f of the ESD450 may vary depending on how close its respective cell segment 422a-f is to the middle of the stack or sub-stack of cell segments. For example, referring to the sub-stack 421a, the innermost cell segment 422b (i.e., the middle cell segment of the 3 assemblies) may include an electrolyte layer formed from a first electrolyte (i.e., electrolyte layer 410b), while the outermost cell segments 422a and 422c (i.e., the outermost cell segments in the sub-stack 421a) may include electrolyte layers formed from a second electrolyte (i.e., electrolyte layers 410a and 410c, respectively). By using a higher conductivity electrolyte in the inner sub-stack, the resistance can be lower and thus less heat can be generated. In this way, thermal control of the ESD is provided by design rather than external cooling techniques.

As another example, the active material used in the electrode layers in each segment of the ESD450 may also vary depending on how close its respective segment 422a-f is to the middle of the stack or sub-stack of segments. For example, referring to sub-stack 421a, the innermost cell segment 422b may include electrode layers (i.e., layers 404a and 408b) formed from a first type of active material having a first temperature and/or rate capability, while the outermost cell segments 422a and 422c may include electrode layers (i.e., layers 414a/408a and layers 404b/405a) formed from a second type of active material having a second temperature and/or rate capability. For example, the ESD stack may be thermally controlled by: for example, the innermost cell segment is constructed with a nickel cadmium electrode that is more heat absorbing, while the outermost cell segment is constructed with a nickel metal hydride electrode that must be cooler. Alternatively, the chemistry or geometry of the ESD may be asymmetric, wherein the cell segment at one end of the stack may be formed of a first active material and have a first height, and the cell segment at the other end of the stack may be formed of a second active material and have a second height.

Furthermore, the geometry of each cell segment of the ESD450 may also vary along the stack of cell segments. In addition to altering the distance between active materials within a particular cell segment, it is also possible that some cell segments 422a-f have a first distance between the active materials of those segments, while other cell segments have a second distance between the active materials of those segments. Regardless, a cell segment or portion in which, for example, there is a smaller distance between active material electrode layers may have a higher power, while a cell segment or portion in which, for example, there is a greater distance between active material electrode layers may have more room for dendrite growth, a longer cycle life, and/or a greater electrolyte reserve. These portions with a larger distance between the active material electrode layers can adjust the charge acceptance of the ESD to ensure, for example, that components with a smaller distance between the active material electrode layers can be charged first.

In an embodiment, the electrode layer geometry of the ESD450 (e.g., positive electrode layers 404a-d, 414a, and 414b, and negative electrode layers 408a-d, 405a, and 405b in fig. 4) may vary along the radial length of the substrate (e.g., substrates 406a-d, 409, 416a, and 416 b). As for fig. 4, the electrode layer thereof is uniform in thickness and symmetrical with respect to the electrode shape. In an embodiment, the electrode layer may be non-uniform. For example, the positive and negative active material electrode layers may vary in thickness with radial position on the surface of the conductive substrate. Non-uniform electrode layers have been discussed in detail in U.S. patent application No.12/258,854 to West et al, the entire contents of which are incorporated herein by reference.

While the stacked ESD embodiments described and illustrated above show a battery segment including a gasket sealed to each of first and second electrode units for sealing an electrolyte therein, it should be noted that each electrode unit of a battery segment may be sealed to its own gasket, and then the gaskets of two adjacent electrodes may be sealed to each other to form a sealed battery segment.

In some embodiments, the gasket may be injection molded to the electrode unit or another gasket so that they may be fused together to form the seal. In some embodiments, the gasket may be ultrasonically welded to the electrode unit or another gasket so that they may together form a seal. In other embodiments, the pad may be heat fused to the electrode unit or another pad, or by heat flow, in which way the pad or electrode unit may be heat fused to another pad or electrode unit. Further, in some embodiments, instead of, or in addition to, creating a grooved portion in the gasket or electrode unit surface to create a seal, the gasket and/or electrode unit may be perforated or have one or more holes through one or more portions thereof. Alternatively, holes, channels or perforations may be provided through a portion of the backing so that a portion of the electrode unit (e.g., the substrate) may be molded to and through the backing. In other embodiments, for example, holes may be made through both the pad and the electrode unit, such that each of the pad and the electrode unit may be molded to and through the other of the pad and the electrode unit.

Although each of the embodiments of stacked ESD described and illustrated above show an ESD formed by stacking substrates having a substantially circular cross-section into a cylindrical ESD, it should be noted that any of a number of shapes may be used to form the substrate of the stacked ESD of the present invention. For example, the stacked ESD of the present 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 can be made therein by those skilled in the art without departing from the scope and spirit of the invention. It will be further understood that various directional and orientational terms, such as "horizontal" and "vertical", "top", "bottom" and "side", "length", "width", "height" and "thickness", "inner" and "outer", and the like, are used herein merely for convenience and are not intended to imply any fixed or absolute directional or orientational limitations on the use of such terms. For example, the devices of the present invention and their individual components may have any orientation. If reoriented, it is necessary to use different directional and orientational terms in their description, but that do not alter their basic nature while remaining within the scope and spirit of the invention. Those skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation. The invention is limited only by the following claims.

Claims (24)

1. An energy storage device, comprising:

a stack of a plurality of electrode units, the stack comprising:

a first sub-stack of a plurality of bipolar electrode units;

a second substack of a plurality of bipolar electrode units collinear with the first substack; and

a monopolar type electrode unit located between the first and second substacks;

a first end cap at a first end of the stack of electrode units; and

a second end cap at a second end of the stack of electrode units.

2. The energy storage device of claim 1, wherein the monopolar type electrode unit is configured to electrically couple the first substack in parallel with the second substack.

3. The energy storage device of claim 1 wherein the polarity of the monopolar type electrode unit is opposite to the polarity of the first and second end caps.

4. The energy storage device of claim 1, wherein the electrode cells of the first substack and the electrode cells of the second substack have separate chemistries.

5. The energy storage device of claim 4, wherein the electrode cells of the first substack are lithium-ion and the electrode cells of the second substack are lead-acid.

6. The energy storage device of claim 1, wherein the bipolar electrode units of the first substack are electrically coupled in series.

7. The energy storage device of claim 1, wherein the bipolar electrode units of the second substack are electrically coupled in series.

8. The energy storage device of claim 1, wherein the first sub-stack is electrically coupled in series with the second sub-stack.

9. The energy storage device of claim 1, wherein each bipolar electrode unit comprises:

a conductive substrate;

a positive active material electrode layer on a first surface of the conductive substrate; and

an anode active material electrode layer on the second surface of the conductive substrate.

10. The energy storage device of claim 1 wherein the monopolar type electrode unit comprises:

an impermeable substrate;

a first active material electrode layer on a first surface of the non-conductive substrate;

a second active material electrode layer on a second surface of the non-conductive substrate, wherein the first layer and the second layer have the same polarity.

11. The energy storage device of claim 10, wherein the impermeable substrate is electrically conductive.

12. The energy storage device of claim 10, wherein the impermeable substrate is non-conductive.

13. The energy storage device of claim 1, wherein an electrolyte layer is disposed between each pair of adjacent electrode units.

14. The energy storage device of claim 1, wherein the first and second substacks have the same number of bipolar electrode units.

15. The energy storage device of claim 14 wherein the unipolar cell is placed centrally within the stack between the first and second substacks.

16. The energy storage device of claim 1, wherein the first and second substacks do not have the same number of bipolar electrode units.

17. The energy storage device of claim 1, further comprising:

a third substack of a plurality of bipolar electrode units, wherein the third substack is placed between the second substack and the second end cap; and

a second monopolar type unit located between the second substack and the second endcap, wherein the second monopolar type electrode unit is configured to electrically couple the first, second, and third substacks in parallel with one another.

18. The energy storage device of claim 1, further comprising:

a third substack of a plurality of capacitors, wherein the third substack is placed between the second substack and the second end cap; and

a second monopolar type unit located between the second substack and the second endcap, wherein the second monopolar type electrode unit is configured to electrically couple the first, second, and third substacks in parallel with one another.

19. The energy storage device of claim 18, wherein the capacitor has a double layer electrode structure.

20. The energy storage device of claim 18, wherein the voltage of the third substack is equal to or greater than the voltage of the energy storage device.

21. An energy storage device, comprising:

a stack of a plurality of electrode units along a stacking axis, the stack comprising:

a monopolar-type electrode unit having first and second surfaces on opposite sides thereof;

a first bipolar electrode unit disposed along the stacking axis, opposite to the first surface;

a second bipolar electrode unit disposed along the stacking axis opposite the second surface, wherein the first and second bipolar electrode units are electrically coupled in parallel via the unipolar electrode units.

22. The energy storage device of claim 21, further comprising a single pair of end caps disposed at opposite ends of the stack.

23. The energy storage device of claim 21 wherein the monopolar type electrode unit has a positive polarity or a negative polarity.

24. The energy storage device of claim 21, wherein an electrolyte layer is disposed between each pair of adjacent electrode units.