CELL PLATES FOR REDOX FLOW BATTERIES

A cell plate of a redox flow battery adapted to provide laminar flow. The cell plate may have a flow frame including a plurality of feed channels interdigitated with a plurality of exhaust channels so as to channel the electrolyte solution through the cell plate and induce proton exchange between a catholyte portion and an anolyte portion. The feed channels and exhaust channels are sized and spaced to manipulate the flowrate and pressure of the electrolyte solution channeled therethrough. In some aspects, the flowrate and pressure are controlled such that the fluid pumps may have a reduced size and speed, thereby reducing the parasitic load on the system and increasing system efficiencies.

INTRODUCTION

The rechargeable flow battery (i.e. a redox flow battery) stores chemical energy in electrolyte solutions that contain electro-active elements. Conversion of this chemical energy to electrical energy may be captured and used for the purposes of powering a variety of devices and/or delivered to a power grid.

A typical rechargeable flow battery will have one or more cells. The cell will have an anolyte solution portion and a catholyte solution portion. These portions are separated by a membrane. Reservoirs containing additional anolyte and catholyte solutions are fluidically coupled to the anolyte portion and catholyte portion of the cell, respectively. As each electrolyte solution is circulated through its respective portion of the cell, the membrane allows for proton exchange between the anolyte solution and the catholyte solution. A current collector (e.g., an electrode) transfers the energy associated with the electron exchange between the anolyte and the catholyte to or from a power source depending on whether the redox-flow battery is being charged or discharged.

Current redox flow technology is limited by several issues. For example, maintaining an efficient electrochemical reaction at the membrane of the redox-flow battery remains a challenge. While a complete transfer of protons for all ions in an electrolyte solution is desired, in some applications, such an exchange may take a significant amount of time. Increasing the reaction time reduces the efficiency (i.e., energy output per time) of the battery. Additionally, flowrate and flow characteristics across the membrane impact the efficiency of the proton exchange across the membrane, which also impacts the efficiency of the battery. As such, it remains desirous to improve the flowrate and flow characteristics of an electrolyte flow-field across a membrane.

It is with respect to these and other considerations that aspects of the technology have been disclosed. Also, although relatively specific problems have been discussed, it should be understood that the technology disclosed herein should not be limited to solving the specific problems identified in the background or the disclosure.

Redox Flow Battery

Aspects of the technology relate to a redox flow battery with a cell plate and a frame, together which form a frame plate assembly. In embodiments, multiple frame plate assemblies are stacked together to form a cell stack. The cell plates are fluidically coupled to the frame of the frame plate assembly. The cell stack is fluidically coupled to a reservoir, in aspects, using manifold inserts (e.g., piping) to provide electrolyte solutions from a cell reservoir to the cell stack. In aspects of the technology, the frame may house an electrolyte pathway which feeds and/or returns electrolytes from a frame channel to a cell plate. Frame channels across frame plates in a cell stack may align to form a combined channel, which channel may feed multiple cell plates of the cell stack.

In aspects of the technology, the cell plate may have a flow frame including a plurality of feed channels interdigitated with a plurality of exhaust channels so as to channel the electrolyte solution through the cell plate and induce proton exchange between a catholyte portion and an anolyte portion. The feed channels and exhaust channels are sized and spaced to manipulate the flowrate and pressure of the electrolyte solution channeled therethrough. In some aspects, the flowrate and pressure are controlled such that the fluid pumps may have a reduced size and speed, thereby reducing the parasitic load on the system and increasing system efficiencies.

These and various other features as well as advantages that characterize the systems and methods described herein will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features are set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the technology. The benefits and features of the technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

DETAILED DESCRIPTION

FIG. 1illustrates an example of a redox-flow battery system100having a cell stack102. As illustrated, the redox-flow battery system100also includes a catholyte reservoir104holding a catholyte solution106and an anolyte reservoir108holding an anolyte solution110. A first pumping mechanism112is used to circulate the catholyte solution106from the catholyte reservoir104to the cell stack102and back via a catholyte pathway114and a second pumping mechanism116is used to circulate the anolyte solution110from the anolyte reservoir108to the cell stack102and back via a anolyte pathway118. Additionally, a catholyte current collector120and an anolyte current collector122are present.

In an embodiment, the redox-flow battery system100may be one of a vanadium- vanadium redox flow battery, a polysulfide bromide battery, an iron-chromium battery, or a manganese-vanadium redox flow battery. In an embodiment where the redox-flow battery system100is a vanadium redox flow battery, the catholyte solution106is substantially V5+in the charged state. Additionally, where the battery is in the charged state, the anolyte solution110is substantially V2+. In an embodiment where the system is a polysulfide bromide battery, the catholyte solution106is substantially sodium tribromide, and the anolyte solution110is substantially sodium disulfide in a charged state. In an embodiment where the system is an iron-chromium battery, the catholyte solution106is substantially Fe3+, and the anolyte solution110is substantially Cr2+in a charged state. In an embodiment where the system is a manganese-vanadium battery, the catholyte solution106is substantially Mn3−, and the anolyte solution110is substantially Vn2+in a charged state. It will be appreciated that the technologies described herein may be used with other redox-flow battery chemistries.

The cell stack102may include a plurality of cell plates as described in further detail below. Each cell plate of the cell stack102facilitates the exchange of electrical energy between the catholyte solution106and the anolyte solution110during a charge/discharge cycle. Each cell plate, which includes a proton exchange membrane positioned between the two electrodes, allows the transfer of a proton from the catholyte solution106to the anolyte solution110during the discharge cycle, and a current collector facilitates the exchange of an electron from the anolyte solution110to the catholyte solution106during the discharge cycle. The cells stack may have cells that are in series or are in parallel. While only one cell stack102is illustrated, it will be appreciated that multiple cell stacks may be electrically coupled together in either series or parallel.

In an embodiment, one or more mechanical pumps are used as the first pumping mechanism112and the second pumping mechanism116to circulate the catholyte solution106and the anolyte solution110, respectively. Other methods and/or equipment may be used to provide circulation of the catholyte solution106between the catholyte reservoir104and the cell stack102, as well as to circulate the anolyte solution110between the anolyte reservoir108and the cell stack102as required or desired. The pumping mechanisms112,116may run on power generated from the battery system100, thus drawing a parasitic load and reducing the efficiency of the system.

As illustrated, the catholyte reservoir104is fluidically coupled to the cell stack102by the catholyte pathway114(which may be a tube, a pipe, or the like), and the anolyte reservoir108is fluidically coupled to the cell stack102by the anolyte pathway118(which may be a tube, a pipe, or the like). It will be appreciated that one or more cell stacks102may be configured to be fluidically coupled together in series and/or parallel as required or desired and as described further below.

FIG. 2illustrates a schematic-perspective view of an example cell stack system200. In aspects of the technology, the cell stack system200includes a plurality of frame plate assemblies201. The plurality of frame plate assemblies201includes a first frame plate assembly202, a second frame plate assembly204, and a third frame plate assembly206, up to an nthor last frame plate assembly208. The plurality of frame plate assemblies201may have any number of frame plate assemblies as required or desired. As illustrated, each frame plate assembly, such as the first frame plate assembly202, the second frame plate assembly204, the third frame plate assembly206, and the last frame plate assembly208are shaped as similar sized rectangular prisms. In alternative examples, each frame plate assembly204,206,206,208may have any other shape, or size, or differing shapes/sizes that enables the cell stack system200to function as described herein.

It will be appreciated that each frame plate assembly has a front face and a back face as described further below. For example, the first frame plate assembly202has a front face210and an opposite back face212. In aspects of the technology, the front face210and the back face212are substantially perpendicularly planar. In aspects of the technology, the back face212of the first frame plate assembly202is disposed proximate to a front face of the second frame plate assembly204, a back face of the second frame plate assembly204is disposed proximate to a front face of the third frame plate assembly206, and so on. Each frame plate assembly includes, in embodiments, a frame and a cell plate (e.g., a monopolar or bipolar plate including carbon paper electrodes and a membrane), which the cell plate is used to facilitate the charging/discharging of a redox flow battery. Various embodiments of the cell plate discussed in further detail below with references toFIGS. 4-9.

The plurality of frame plate assemblies201may be coupled together using one or more framing members216. For example, the back face212of the first frame plate assembly202may be coupled to the front face of the second frame plate assembly204using one or more framing members216that also couples the back face of the second frame plate assembly204to the front face of the third frame plate assembly206, and so on.

Coupling may occur through a variety of means. As illustrated, the plurality of frame plate assemblies201are coupled together using framing rods216. The framing rods216orthogonally penetrate the front face210and the back face212of the first frame plate assembly202. The framing rod216is a type of framing member216. In aspects of the technology, the framing members216may be rods, plates, walls, shafts, and/or any item capable of coupling each of the plurality of frame plate assemblies201to adjacent frame plate assemblies. In aspects of the technology, the first frame plate assembly202has a plurality of bores operable to receive the plurality of framing rods216. Additionally, fasteners218couple the framing rods216to the first frame plate assembly202. Though the illustrated fasteners218are bolts that couple to a threaded end of the framing rods216, it will be appreciated that other fastening technology is contemplated.

Similarly, the second frame plate assembly204has a plurality of bores, which bores may be aligned with the bores of the first frame plate assembly202such that the plurality of framing rods216may be received. In alternative embodiments, other framing members may be used. The other frame plate assemblies in the plurality of frame plate assemblies201may have similarly aligned bores to receive the framing rods216. As such, each frame plate assembly of the plurality of frame plate assemblies201may couple to the adjacent frames by sliding over the framing rods216.

As illustrated, the plurality of framing rods216may be secured to a first mounting plate220. The first mounting plate220may cap the top of the plurality of frame plate assemblies201. That is, the first mounting plate220may be disposed on the front face210of the first frame plate assembly202. Similarly, a second mounting plate222may cap the bottom of the plurality of frame plate assemblies201. That is, the second mounting plate222may be disposed on the back face of the last frame plate assembly208and opposite the first mounting plate220.

Additionally illustrated inFIG. 2is electrolyte piping224and226. The electrolyte piping fluidically couples an electrolyte reservoir, such as an anolyte reservoir or a catholyte reservoir as described above, to the plurality of frame plate assemblies201. As illustrated, the electrolyte piping224and the electrolyte piping226penetrate through the first frame plate assembly202through an angle orthogonal to the front face210and the back face212. The electrolyte piping224may deliver and/or return the electrolyte solution to each frame plate assembly in the plurality of frame plate assemblies201. The electrolyte piping224,226may be a separate component, as illustrated, or may be formed piecewise through the stacking of the plurality of frame plate assemblies201and as described further below.

The reservoirs may be the same as or similar to the electrolyte reservoirs described with references toFIG. 1. In aspects of the technology, each frame plate assembly is designed with a pathway such that an electrolyte solution may pass from the frame of a frame plate assembly to a cell plate of the frame plate assembly, and then out of the frame plate assembly, and then ultimately to an electrolyte reservoir.

FIG. 3Aillustrates an example catholyte pathway between multiple frame plate assemblies of a redox cell stack300. In aspects of the technology, a catholyte solution302enters a first frame plate assembly304. The first frame plate assembly304may have a frame with a variety of channels, vias, membranes, porous material, and/or pathways to direct the flow of the catholyte solution302across a portion of the backside of the first frame plate assembly304. In aspects, flow may be directed through a frame of the first frame plate assembly304into a cell portion of the first frame plate assembly304. In aspects of the technology, flow into the cell portion of the first frame plate assembly304is directed across a backside of the membrane of the cell portion of the first frame plate assembly304. Flow of the catholyte solution may be directed such that a laminar sheet-flow occurs across the backside of a membrane of a cell portion of the first frame plate assembly304.

The catholyte solution302may also enter a second frame plate assembly306. In aspects of the technology, the frame of the second frame plate assembly includes channels, vias, membranes, porous materials, and or/pathways to direct the flow of the catholyte solution302across a portion of a backside of the second frame plate assembly. Flow of302may enter and exit the second frame plate assembly306in a similar manner as the first frame plate assembly304. In aspects, flow may be directed through a frame of the second frame plate assembly306into a cell portion of the second frame plate assembly. In aspects of the technology, flow into the cell portion of the second frame plate assembly306is directed across a backside of the membrane of the cell portion of the second frame plate assembly306. Flow of the catholyte solution302may be directed such that a laminar sheet-flow occurs across the backside of a membrane of the cell portion of the second frame plate assembly306.

This pattern of flow of the catholyte solution302may proceed to a plurality of other frame plate assemblies, including a third frame plate assembly308, such that the catholyte solution302is channeled through each frame plate assembly as a parallel flow. Flow of the catholyte solution302may enter and exit the third frame plate assembly308in a similar manner as the first and second frame plate assembles304,306. In aspects of the technology, the catholyte solution302enters a frame plate assembly and flow may be directed such that the catholyte solution flows down a backside portion of the membrane of a cell portion of a plate assembly. Once the catholyte solution302is channeled through the frame plate assemblies, the exhausted catholyte solution is then returned the reservoir.

Illustrated inFIG. 3Bis a flow of an anolyte solution310. The anolyte solution310may travel from the first frame plate assembly304to the third frame plate assembly308and generally in a similar direction as the catholyte solution described above. The first frame plate assembly304may have a frame with a variety of channels, vias, membranes, porous material, and/or pathways to direct the flow of the anolyte solution310across a portion of the front side of the first frame plate assembly304. In aspects, flow may be directed through a frame of the first frame plate assembly304into a cell portion of the first frame plate assembly304. In aspects of the technology, flow into the cell portion of the first frame plate assembly304is directed across a front side of the membrane of the cell portion of the first frame plate assembly304such that the flow of the anolyte solution310is opposite of the flow of the catholyte solution within the cell plate while each flow is separated. Flow of the anolyte solution310may be directed such that a laminar sheet flow occurs across the front side of the membrane of the cell portion of the first frame plate assembly304.

The anolyte solution310may also enter the second frame plate assembly306. Flow of the anolyte solution310may enter and exit the second frame plate assembly306in a similar manner as the first frame plate assembly304. In aspects of the technology, the frame of the second frame plate assembly306includes channels, vias, membranes, porous materials, and or/pathways to direct the flow of the anolyte solution310across a front side of the second frame plate assembly306. In aspects, flow may be directed through a frame of the second frame plate assembly306in a cell portion of the second frame plate assembly306. In aspects of the technology, flow into the cell portion of the second frame plate assembly306is directed across a front side of the membrane of the cell portion of the second frame plate assembly306. Flow of the anolyte solution310may be directed such that a laminar sheet flow occurs across the front side of a membrane of the cell portion of the second frame plate assembly306.

This pattern of flow of the anolyte solution310may proceed to a plurality of other frame plate assemblies, including a third frame plate assembly308, such that the anolyte solution310is channeled through each frame plate assembly as a parallel flow. Flow of the anolyte solution310may enter and exit the third frame plate assembly308in a similar manner as the first and second frame plate assembles304,306. In aspects of the technology, the anolyte solution310enters a frame plate assembly and flow may be directed such that the anolyte solution flows down a frontside portion of the membrane. Once the anolyte solution310is channeled through the frame plate assemblies, the exhausted anolyte solution is then returned the reservoir.

In aspects of the technology, the catholyte solution302flows through a shared manifold (not shown). That is, in an example, each cell includes a flow path that enables an electrolyte to flow from an inlet to an outlet, and each frame plate assembly has an internal manifold insert, such as the electrolyte piping (shown inFIG. 2). Thus, stacking multiple frame plate assemblies may create a common supply and return manifolds via the electrolyte piping. This internal manifold supplies and returns electrolyte to the individual cells in a parallel flow configuration, in example embodiments. Other configurations are contemplated.

FIGS. 3A and 3Billustrate the redox cell stack300as including three frame plate assemblies304,306,308. In the example, each frame plate assembly includes a bipolar plate such that the catholyte solution302and the anolyte solution310can both separately flow through a single plate of the frame plate assemblies. In some examples, the redox cell stack may include a leading frame plate assembly positioned adjacent to the first frame plate assembly304and a trailing frame plate assembly positioned adjacent to the third frame plate assembly308, which are each a monopolar plate. This enables the outer electrolyte flows (e.g., the frontside anolyte solution310flow of the first frame plate assembly304and the backside catholyte solution302flow of the third frame plate assembly308) to transfer protons during flow through the cell and every electrolyte solution flow is used to charge or discharge the battery. The monopolar plate enables a single electrolyte solution flow through the frame plate assembly, for example, either the catholyte solution302or the anolyte solution310. In other examples, the redox cell stack300may include two monopolar plates for each cell.

FIG. 4illustrates a plan view of an example frame plate assembly400. As illustrated, the frame plate assembly400includes a frame402coupled in fluidic communication to a cell plate404. The frame402is a substantially shaped as a rectangular prism and may be made out of a variety of materials, such as a rigid or semi-rigid plastic. In some examples, the frame402may be constructed out of electrical isolating and heat conducting material. The frame402has a substantially planar front face and a substantially planar back face so that it may be stacked in a redox cell stack as described above. In other examples, some or the entire frame402may be removed to aid in heat exchange of the cell plate404and the atmosphere (or other environment).

A frame channel406is defined at each corner of the frame402. The frame channels406may be coupled to adjacent frame channels of adjacent frame assemblies to form a tube or channel throughout a redox cell stack for which electrolyte solution can be delivered and/or returned through the redox cell stack. Electrolyte pathways408extend between the frame channel406and the cell plate404so that the cell plate404is fluidically coupled to the electrolyte reservoir as described above. In the example, the electrolyte pathways408extend between a frame channel end410and a cell plate end412. The frame channel end410fluidically couples the electrolyte pathways408to the frame channel406and the cell plate end412fluidically couples the electrolyte pathway408to the cell plate404. As illustrated, the electrolyte pathways408may be a cutaway defined within the frame402along with a substantially inert tubing that couples to the frame channel end410and couples to the cell plate end412via any connection type, such as press fit, snap fit, or threaded connection. The tubing is configured to channel an electrolyte flow therethrough, and may include polyurethane, polypropylene, or any other inert material. In other examples, the electrolyte pathways408may be formed using gas assisted molding such that the electrolyte pathway408is formed as a unitary construction with the frame402.

For example, a catholyte supply pathway may be defined by a first frame channel406A to deliver a catholyte solution to the cell plate404via a first electrolyte pathway408A. An anolyte supply pathway may be defined by a second frame channel406B to deliver an anolyte solution to the cell plate404via a second electrolyte pathway408B. An anolyte return pathway may be defined by a third frame channel406C to receive the exhausted anolyte solution from the cell plate404and return the exhausted anolyte solution to the anolyte reservoir. A catholyte return pathway may be defined by a fourth frame channel406D to receive the exhausted catholyte solution from the cell plate404and return the exhausted catholyte solution to the catholyte reservoir. As such, the cell plate404as illustrated is a bipolar plate, however, the frame plate assembly could be configured for use with two monopolar plates or with a single monopolar plate and a single electrolyte solution (either the catholyte solution or the anolyte solution) being channeled therethrough.

Additionally illustrated, are a plurality of bores414that are circular cut-outs adapted to receive framing members, such as rods, as described above. The frame plate assembly400may include a floating frame plate assembly as described in U.S. Patent Application No. 62/518,953 filed Jun. 13, 2017 and entitled “FLOATING FRAME PLATE ASSEMBLY,” the disclosure of which is hereby incorporated by reference herein in its entirety.

FIG. 5illustrates a partial perspective view of an example bipolar cell plate500.FIG. 6illustrates another partial perspective view of the bipolar cell plate500within a frame plate assembly502, which is similar to the assembly described above. Referring concurrently toFIGS. 5 and 6, the cell plate500is a substantially rectangular prism with a front face504and an opposite back face506. A frame508defines the perimeter of the cell plate500with an orifice510formed on each exterior side of the frame508. The orifice510is sized and shaped to couple to an electrolyte pathway512, which is similar to the pathways described above, such that a flow of electrolyte solution may be received and discharged from the cell plate500. Within the frame508, the cell plate500includes a distributed flow field area514defined on the front face504. In the example, the flow field area514is substantially rectangular, although, in other examples, the flow field area may be any other shape as required or desired. The flow field area514facilitates channeling an electrolyte solution over the front face504and across a membrane (not shown) so that proton exchange is enabled and energy transfer occurs within the system as described above.

Within the flow field area514, a plurality of feed channels516are defined in the cell plate500and a plurality of exhaust channels518are defined in the cell plate500. In the examples, the feed channels516are interdigitated with the exhaust channels518so that the feed channels516alternate with the exhaust channels518and each feed channel516is positioned next to the exhaust channels518and vice versa. Additionally, the feed channels516and the exhaust channels518are separated and substantially parallel to one another and extend linearly across the flow field area514. In alternative examples, the channels may have any other configuration along the flow field area514. For example, the channels may be parallel to one another; however, the channels may be S-shaped, zig-zag shaped, dog-leg shaped, etc. across the flow field area514. In other examples, the channels may not be parallel to one another and/or may be tapered.

Each feed channel516extends between an inlet end520and a termination end522. At the inlet end520, an inlet opening524is defined that is in fluid communication with a respective supply orifice510. At the termination end522, the feed channel516does not have any openings and the feed channel516merely ends. Each exhaust channel518extends between a commencement end526and a discharge end528. At the commencement end526, the exhaust channel518does not have any openings and the exhaust channel518merely begins. At the discharge end528, a discharge opening530is defined that is in fluid communication with a respective return orifice510. In the example, the frame508has interior channels (not shown) defined within its body that extend between the orifice510and either the inlet openings524or the discharge openings530to form a portion of the electrolyte pathways. In alternative embodiments, the channel between the orifice and either the inlet openings or the discharge openings may be formed on an exterior surface of the frame. The inlet ends520of the feed channels516are offset from the commencement ends526of the exhaust channels518and the discharge ends528of the exhaust channels518are offset from the termination ends522of the feed channels516, so that the interior channels may be formed within the cell plate500.

In the example, the back face506of the cell plate500also includes a similar flow field area (not shown) with feed channels and exhaust channels so that a second electrolyte solution can be channeled over the back face and across a membrane for proton exchange as described above. For example, a catholyte supply pathway may be defined by a first orifice510A to deliver a catholyte solution to the feed channels516of the front flow field area514. An anolyte supply pathway may be defined by a second orifice510B to deliver an anolyte solution to the feed channels of the back flow field area (not shown). An anolyte return pathway may be defined by a third orifice510C to receive the exhausted anolyte solution from the exhaust channels of the back flow field area. A catholyte return pathway may be defined by a fourth orifice510D to receive the exhausted catholyte solution from the exhaust channels518of the front flow field area514. Furthermore, the cell plate500includes a porous electrode and a membrane (both shown and describes inFIGS. 7 and 8) that covers the flow field area on the front face and the back face so that electrolyte flow is contained within the cell plate500. In alternative examples, the cell plate may be a monopolar cell plate which only has the flow field area on one face of the cell plate.

FIG. 7illustrates a cross-sectional schematic view of the bipolar cell plate500.FIG. 8illustrates a partial perspective schematic view of the bipolar cell plate500. Referring concurrently toFIGS. 7 and 8, the cell plate500includes a plate structure532having a first surface534and an opposite second surface536. The plate structure532is formed from a material, for example, graphite or a graphite composite material, which is dense, electrically conductive, and inert in the electrolyte solutions, including under electrochemical stress. In the example, the plate structure532also forms the frame508(shown inFIGS. 5 and 6), although in alternative examples, the plate structure532and the frame508may be formed from different materials.

A first flow frame538is coupled between the plate structure532and a first porous electrode540adjacent the first surface534. The first flow frame538extends from the first surface534to the first electrode540and is the layer in which the feed channels516and exhaust channels518are defined, which enable a flow of electrolyte solution into and out of the flow field area as described above. Between each channel516,518, the first flow frame538includes a plurality of ribs542that extend from the first surface534to the first electrode540. In the example, the plate structure532is unitary with the flow frame538such that the channels516,518are defined therein. In alternative examples, the flow frame538and the plate structure532may be formed from different materials. The first porous electrode540is a conductive substrate, such as a carbon paper, that enables the flow of electrolyte solution therethrough. For example, the electrode540may have a pocket depth of between approximately200micrometers to approximately300micrometers. A polymeric membrane separator544, such as Nafion, a thin ion-porous membrane, is positioned adjacent to the electrode540so as to separate the electrode540from adjacent cell plates and other electrodes.

In an example, a monopolar cell plate includes only one flow frame as described, so that the cell plate facilitates only one flow of electrolyte solution therethrough. However, as illustrated, the cell plate500is a bipolar cell plate and thus includes a second flow frame546coupled between the plate structure532and a second porous electrode548adjacent the second surface536. The second flow frame546extends from the second surface536to the second electrode548and is the layer in which the feed channels516, exhaust channels518, and ribs542are defined, which enable a flow of electrolyte solution into and out of the flow field area. The second porous electrode548is a conductive substrate, such as a carbon paper, that enables the flow of electrolyte solution therethrough. The membrane544is positioned adjacent to the electrode548so as to separate the electrode548from adjacent cell plates and other electrodes.

In operation, for the bipolar cell plate500, separated electrolyte solution flows550are pumped through from separate reservoirs so that electrical energy may be exchanged between the two solutions at the cell plate500. For example, a catholyte solution is channeled through a supply pathway and into the respective feed channels516on the first surface534and an anolyte solution is channeled through a supply pathway and into the respective feed channels516on the second surface536. Because the feed channels516are separated from the exhaust channels518, a portion552of the electrolyte solution flow550is channeled through the porous electrode540,548and around the ribs542to either side of the feed channel516. As the electrolyte solution flow552passes by the membrane544, protons are transferred between adjacent electrolyte solution flows of the catholyte solution and the anolyte solution. The electrolyte solution flow552then is channeled554through the exhaust channels518and out of the cell plate500to the return pathway. Additionally, a portion of the rib542may be porous such that a portion556of the electrolyte solution flow550from the feed channel516is channeled through the rib542and directly into the exhaust channel518without flowing through the electrode540.

Electrolyte solution flow through the cell plate500may be defined by many variables, including pressure drop from inlet to outlet, pump specifications and speed, electrolyte viscosity and temperature, and electrode porosity, thickness, and compression. In some examples, to increase proton exchange efficiencies, uniform electrolyte solution flow adjacent to the membrane544is desired. For example, forming a high pressure drop of the electrolyte solution flow at the inlet openings to the feed channels516forms this desired uniform flow. However, increasing electrolyte solution flowrate to generate high pressure drop increases parasitic energy consumption of the system because higher pressure pumps are required. Accordingly, in the example, a channel width558is sized with respect to a rib width560so as to reduce the pressure drop of the electrolyte solution flow into the flow field area while maintaining uniform flow. By reducing the pressure drop of the electrolyte solution flow, a lower flowrate of the electrolyte solution flow may be utilized, thereby reducing parasitic energy consumption of the system because lower pressure pumps may be used.

In the example, the feed channel516and the exhaust channel518have a substantially equal channel width558and as such the flow frames538,546are formed with a ratio of rib width560to channel width558in a range from approximately 1:1 to approximately 1:4. As such, the electrolyte solution flowrate and pressure through the cell plate500is reduced, thereby reducing parasitic energy consumption of the pumps while increasing electrolyte utilization and increasing system efficiencies. In some examples, the ratio of the rib width560to channel width558is in a range from approximately 1:2 to approximately 1:3. In other examples, the ratio of the rib width560to channel width558may be approximately 1:1, 1:2, 1:3, or 1:4.

FIG. 9illustrates a partial perspective schematic view of an example redox cell stack600. The redox cell stack600may include a plurality (e.g., thirty) of bipolar cell plates602stacked together such that a catholyte poriton604is formed on one side of the cell plate602and an anolyte poriton606is formed on the opposite side of the cell plate602. In this example, the cell plates are bipolar; however, it is appreciated that a plurality of monopolar cell plates stacked together may also be used. As described in detail above, each cell plate602has a plate structure608with a plurality of catholyte feed channels610and exhaust channels612separated by ribs614and a catholyte electrode616covering the channels610,612on one face. Additionally, the plate structure608has a plurality of anolyte feed channels618and exhaust channels620separated by ribs622and an anolyte electrode624covering the channels618,620on the opposite face. Between each catholyte electrode614and anolyte electrode624is a membrane626so that electrolyte solution flow is restricted from passing between the catholyte poriton604and the anolyte poriton606.

In operation, the catholyte feed channels610receive a flow of catholyte solution628that is directed630around the ribs614and through the catholyte electrode616to the catholyte exhaust channels612as an exhaust flow632. Additionally, the anolyte feed channels618receive a flow of anolyte solution634that is directed636around the ribs622and through the anolyte electrode624to the anolyte exhaust channels620as an exhaust flow638. When the catholyte solution630and the anolyte solution636pass by the membrane626, protons may be exchanged640between the solutions for battery operation. In the example, the feed and exhaust channels in both the catholyte poriton604and the anolyte poriton606extend in substantially the same orientation with respect to the plate structure608. As such, the catholyte solution and the anolyte solution both flow in the same direction across the cell plate. In alternative examples, the cathode604and anode606may have different or even opposite orientations on the cell plate so that the catholyte solution and the anolyte solution flow is in substantially orthogonal or opposing directions.

As described above, to increase battery efficiency the ratio of rib width to channel width is defined between 1:1 and 1:4. In other examples, the ratio of rib width to channel width is defined between 1:2 and 1:3. In yet other examples, the ratio of rib width to channel width is defined as approximately 1:4, also in this example, the electrodes616,624may have a pocket depth of between 200-300 micrometers, and under a compression of between 10-40% of a thickness of the electrodes616,624.

FIGS. 10A and 10Billustrate graphical views of the efficiency of the redox cell stack600(shown inFIG. 9).FIG. 10Ais a graph642illustrating a relationship between pump speed644along the x-axis and normalized discharge energy646along the y-axis. A first curve648shows the comparison between pump speed644and normalized discharge energy646for a cell plate with a ratio of rib width to channel width of 1:1. A second curve650shows the comparison between pump speed644and normalized discharge energy646for a cell plate with a ratio of rib width to channel width of 1:2. A third curve652shows the comparison between pump speed644and normalized discharge energy646for a cell plate with a ratio of rib width to channel width of 1:4. As illustrated, as the ratio of rib width to channel width increases, the pump speed644required for the same normalized discharge energy646decreases, thereby leading to higher system efficiency because there is a decrease in required pump power and a reduction of the parasitic load of the system.

FIG. 10Bis a graph654illustrating a relationship between pump speed656along the x-axis and stack efficiency658along the y-axis. A first curve660shows the comparison between pump speed656and stack efficiency658for a cell plate with a ratio of rib width to channel width of 1:1. A second curve662shows the comparison between pump speed656and stack efficiency658for a cell plate with a ratio of rib width to channel width of 1:2. A third curve664shows the comparison between pump speed656and stack efficiency658for a cell plate with a ratio of rib width to channel width of 1:4. As illustrated, as the ratio of rib width to channel width increases, the pump speed656required for the same stack efficiency658decreases, thereby leading to higher system efficiency because there is a decrease in required pump power and a reduction of the parasitic load of the system. By increasing the rib width to channel width, stack efficiencies of around 80% or greater are obtainable with a pump speed of less than 4 mL/min/cm2that has a flowrate of less than 40 psi, and even with a pump speed of less than 2 mL/min/cm2that has a flowrate of less than 20 psi.

FIG. 11illustrates a flowchart of an example method700of manufacturing a cell plate. The method700includes defining a flow frame on a surface of a plate structure (operation702). The flow frame may include a rib such that a feed channel and an exhaust channel are defined in the flow frame and the feed channel is interdigitated with the exhaust channel. The feed channel being configured to receive a flow of electrolyte solution and the exhaust channel being configured to discharge the flow of electrolyte solution. A porous electrode is coupled to the flow frame (operation704) such that the flow frame extends between the plate structure and the electrode. The electrode being configured to channel at least a portion of the flow of electrolyte solution around the rib from the feed channel to the exhaust channel.

In some examples, the rib has a first width defined between the feed channel and the exhaust channel, and the feed channel and the exhaust channel have a second width defined between the ribs. The method may also include forming the rib with a ratio of the first width to the second width in a range from approximately 1:1 to approximately 1:4 (operation706). In other examples, the ratio of the first width to the second width is formed in a range from approximately 1:2 to approximately 1:3 (operation708).

The method may also include defining a second flow frame on a second surface of the plate structure(operation710). The second flow frame includes a rib such that a feed channel and an exhaust channel are defined in the second flow frame, and the feed channel is interdigitated with the exhaust channel. The feed channel being configured to receive a second flow of electrolyte solution and the exhaust channel being configured to discharge the second flow of electrolyte solution. A second porous electrode is coupled to the second flow frame (operation712) such that the second flow frame extends between the plate structure and the second electrode. The second electrode being configured to channel at least a portion of the second flow of electrolyte solution around the rib from the feed channel to the exhaust channel.

In some examples, an ion-porous membrane is positioned adjacent the electrode opposite the flow frame (operation714). In other examples, at least a portion of the flow frame is formed from a porous material (operation716). In yet other examples, the feed channel is defined substantially parallel to the exhaust channel in the flow frame (operation718).