Patent Application
20100203384
This invention relates generally to energy storage devices (ESDs) and, more particularly, this invention relates to stacked ESDs with electrode folds.
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.
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.
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:
Apparatus and methods are provided for stacked energy storage devices (ESDs) with increased capacity, and are described below with reference to
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.
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.
With continued reference to the stacked state of BPUs 202 in
As shown in
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 2a/2d, and the electrolyte layer 10a/10e therebetween, as shown in
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 10a of cell segment 22a) from combining with the electrolyte of another cell segment (see, e.g., electrolyte layer 10b of cell segment 22b), 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
In sealing the cell segments of stacked bi-polar ESD 50 to prevent electrolyte of a first cell segment (see, e.g., electrolyte layer 10a of cell segment 22a) from combining with the electrolyte of another cell segment (see, e.g., electrolyte layer 10b of cell segment 22b), cell segments may produce a pressure differential between adjacent cells (e.g., cells 22a/22b) 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.
In the stack of
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 404h or height 408h, 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
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.
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 522a-b. For example, there may be a greater number of interfaces between positive electrode layer 504 and negative electrode layer 508 in cell segment 522a than the number of interfaces in a cell segment in
As illustrated in
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.
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 622a-b. For example, there may be a greater number of interfaces between positive electrode layer 604 and negative electrode layer 608 in cell segment 622a than the number of interfaces in a cell segment in
As shown in
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 751a-c of
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
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 606a of
As discussed above in connection with
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.
The portions of electronic raceway 901 that are not coupled to electrode segments 905a-c may be folded into folded portions 952a and 952b as shown in
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 905a-c). For example, a separator sleeve may be ultrasonically welded around electrode segment 905a. Any other suitable technique, or combination of techniques, may be used to fit and/or fasten the separator sleeve around electrode segment 905a.
As shown, each of electrode segments 905a-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 905a-c provided on electronic raceway 901. For example, although the cross-sectional areas of the electrode segments of
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
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
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
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
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
Inserting tabs and/or attaching the electronic raceway to the electrode segments (see, e.g., electrode segments 905a-c of
The substrates used to form the electrode units of the invention (e.g., substrates 6a-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 4a-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 8a-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 901a) 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 60a-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
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
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 22a-e is to the middle of the stack of cell segments. For example, innermost cell segment 22c may include electrode layers (i.e., layers 8b and 4c) formed of a first type of active materials having a first temperature and/or rate performance, while middle cell segments 22b and 22d may include electrode layers (i.e., layers 8a/4b and layers 8c/4d) formed of a second type of active materials having a second temperature and/or rate performance, while outermost cell segments 22a and 22e may include electrode layers (i.e., layers 38/4a and layers 8d/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 22a-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 4a-d and 14, and negative layers 8a-8d and 38 of
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 61147725 | Jan 2009 | US | |
| 61181194 | May 2009 | US |
