Flow batter with radial electrolyte distribution

An electrochemical flow cell includes a permeable electrode, an impermeable electrode located adjacent to and spaced apart from the permeable electrode and a reaction zone electrolyte flow channel located between a first side of the permeable electrode and a first side of the impermeable electrode. The electrochemical flow cell also includes at least one electrolyte flow channel located adjacent to a second side of the permeable electrode, at least one central electrolyte flow conduit extending through a central portion of the permeable electrode and through a central portion of the impermeable electrode and at least one peripheral electrolyte flow inlet/outlet located in a peripheral portion of the electrochemical cell above or below the permeable electrode.

FIELD

The present invention is directed to electrochemical systems and methods of using same.

BACKGROUND

The development of renewable energy sources has revitalized the need for large-scale batteries for off-peak energy storage. The requirements for such an application differ from those of other types of rechargeable batteries such as lead-acid batteries. Batteries for off-peak energy storage in the power grid generally are required to be of low capital cost, long cycle life, high efficiency, and low maintenance.

One type of electrochemical energy system suitable for such an energy storage is a so-called “flow battery” which uses a halogen component for reduction at a normally positive electrode, and an oxidizable metal adapted to become oxidized at a normally negative electrode during the normal operation of the electrochemical system. An aqueous metal halide electrolyte is used to replenish the supply of halogen component as it becomes reduced at the positive electrode. The electrolyte is circulated between the electrode area and a reservoir area. One example of such a system uses zinc as the metal and chlorine as the halogen.

Such electrochemical energy systems are described in, for example, U.S. Pat. No. 3,713,888, 3,993,502, 4,001,036, 4,072,540, 4,146,680, and 4,414,292, and in EPRI Report EM-I051 (Parts 1-3) dated April 1979, published by the Electric Power Research Institute, the disclosures of which are hereby incorporated by reference in their entirety.

SUMMARY

An embodiment relates to an electrochemical flow cell. The electrochemical flow cell includes a permeable electrode, an impermeable electrode located adjacent to and spaced apart from the permeable electrode and a reaction zone electrolyte flow channel located between a first side of the permeable electrode and a first side of the impermeable electrode. The electrochemical flow cell also includes at least one electrolyte flow channel located adjacent to a second side of the permeable electrode, at least one central electrolyte flow conduit extending through a central portion of the permeable electrode and through a central portion of the impermeable electrode and at least one peripheral electrolyte flow inlet/outlet located in a peripheral portion of the electrochemical cell above or below the permeable electrode.

Another embodiment relates to a flow battery having a pressure vessel and a stack of electrochemical flow cells located in the pressure vessel. The flow battery also includes a reservoir located in the pressure vessel, the reservoir configured to accumulate a metal halide electrolyte component and a liquefied halogen reactant and a flow circuit located in the pressure vessel, the flow circuit configured to deliver the halogen reactant and the metal halide electrolyte between the reservoir and the stack of electrochemical cells.

Yet another embodiment relates to a method of operating a flow battery comprising of a stack of electrochemical flow cells. The method includes providing a radial flow of a metal halide electrolyte component and a liquefied halogen reactant between at least one peripheral inlet located in a peripheral portion of a reaction zone electrolyte flow channel of at least one cell in the stack and at least one central outlet located in a central portion between adjacent cells in the stack.

DETAILED DESCRIPTION

The following documents, the disclosures of which are incorporated herein by reference in their entirety, can be useful for understanding and practicing the embodiments described herein: U.S. patent application Ser. No. 12/523,146, which is a U.S. National Phase entry of PCT application no. PCT/US2008/051111 filed Jan. 11, 2008, which claims benefit of priority to U.S. patent application Ser. No. 11/654,380 filed Jan. 16, 2007.

The embodiments disclosed herein relate to an electrochemical system (also sometimes referred to as a “flow battery”). The electrochemical system can utilize a metal-halide electrolyte and a halogen reactant, such as molecular chlorine. The halide in the metal-halide electrolyte and the halogen reactant can be of the same type. For example, when the halogen reactant is molecular chlorine, the metal halide electrolyte can contain at least one metal chloride.

The electrochemical system can include a sealed vessel containing an electrochemical cell in its inner volume, a metal-halide electrolyte and a halogen reactant, and a flow circuit configured to deliver the metal-halide electrolyte and the halogen reactant to the electrochemical cell. The sealed vessel can be a pressure vessel that contains the electrochemical cell. The halogen reactant can be, for example, a molecular chlorine reactant.

In many embodiments, the halogen reactant may be used in a liquefied form. The sealed vessel is such that it can maintain an inside pressure above a liquefication pressure for the halogen reactant at a given ambient temperature. A liquefication pressure for a particular halogen reactant for a given temperature may be determined from a phase diagram for the halogen reactant. For example,FIG. 4presents a phase diagram for elemental chlorine, from which a liquefication pressure for a given temperature may be determined. The system that utilizes the liquefied halogen reactant in the sealed container does not require a compressor, while compressors are often used in other electrochemical systems for compression of gaseous halogen reactants. The system that utilizes the liquefied halogen reactant does not require a separate storage for the halogen reactant, which can be located outside the inner volume of the sealed vessel. The term “liquefied halogen reactant” refers to at least one of molecular halogen dissolved in water, which is also known as wet halogen or aqueous halogen, and “dry” liquid molecular halogen, which is not dissolved in water. Similarly, the term “liquefied chlorine” may refer to at least one of molecular chlorine dissolved in water, which is also known as wet chlorine or aqueous chlorine, and “dry” liquid chlorine, which is not dissolved in water.

In many embodiments, the system utilizes a liquefied molecular chlorine as a halogen reactant. The liquefied molecular chlorine has a gravity which is approximately two times greater than that of water.

The flow circuit contained in the sealed container may be a closed loop circuit that is configured to deliver the halogen reactant, preferably in the liquefied or liquid state, and the at least one electrolyte to and from the cell(s). In many embodiments, the loop circuit may be a sealed loop circuit. Although the components, such as the halogen reactant and the metal halide electrolyte, circulated through the closed loop are preferably in a liquefied state, the closed loop may contain therein some amount of gas, such as chlorine gas.

Preferably, the loop circuit is such that the metal halide electrolyte and the halogen reactant circulate through the same flow path without a separation in the cell(s).

Each of the electrochemical cell(s) may comprise a first electrode, which may serve as a positive electrode in a normal discharge mode, and a second electrode, which may serve as a negative electrode in a normal discharge mode, and a reaction zone between the electrodes.

In many embodiments, the reaction zone may be such that no separation of the halogen reactant, such as the halogen reactant or ionized halogen reactant dissolved in water of the electrolyte solution, occurs in the reaction zone. For example, when the halogen reactant is a liquefied chlorine reactant, the reaction zone can be such that no separation of the chlorine reactant, such as the chlorine reactant or chlorine ions dissolved in water of the electrolyte solution, occurs in the reaction zone. The reaction zone may be such that it does not contain a membrane or a separator between the positive and negative electrodes of the same cell that is impermeable to the halogen reactant, such as the halogen reactant or ionized halogen reactant dissolved in water of the electrolyte solution. For example, the reaction zone may be such that it does not contain a membrane or a separator between the positive and negative electrodes of the same cell that is impermeable to the liquefied chlorine reactant, such as the chlorine reactant or chlorine ions dissolved in water of the electrolyte solution.

In many embodiments, the reaction zone may be such that no separation of halogen ions, such as halogen ions formed by reducing the halogen reactant at one of the electrodes, from the rest of the flow occurs in the reaction zone. In other words, the reaction zone may be such that it does not contain a membrane or a separator between the positive and negative electrodes of the same cell that is impermeable for the halogen ions, such as chlorine ions. Furthermore, the cell may be a hybrid flow battery cell rather than a redox flow battery cell. Thus, in the hybrid flow battery cell, a metal, such as zinc is plated onto one of the electrodes, the reaction zone lacks an ion exchange membrane which allows ions to pass through it (i.e., there is no ion exchange membrane between the cathode and anode electrodes) and the electrolyte is not separated into a catholyte and anolyte by the ion exchange membrane.

In certain embodiments, the first electrode may be a porous electrode or contain at least one porous element. For example, the first electrode may comprise a porous carbonaceous material such as a porous carbon foam. In a discharge mode, the first electrode may serve as a positive electrode, at which the halogen may be reduced into halogen ions. The use of the porous material in the first electrode may increase efficiency of the halogen reactant's reduction.

In many embodiments, the second electrode may comprise an oxidizable metal, i.e., a metal that may be oxidized to form cations during the discharge mode. In many embodiments, the second electrode may comprise a metal that is of the same type as a metal ion in one of the components of the metal halide electrolyte. For example, when the metal halide electrolyte comprises zinc halide, such as zinc chloride, the second electrode may comprise metallic zinc. Alternatively, the electrode may comprise another material, such as ruthenized titanium (i.e., ruthenium coated titanium, where the ruthenium is oxidized to form ruthenium oxide) that is plated with zinc. In such a case, the electrochemical system may function as a reversible system.

Thus, in some embodiments, the electrochemical system may be reversible, i.e. capable of working in both charge and discharge operation mode; or non-reversible, i.e. capable of working only in a discharge operation mode. The reversible electrochemical system usually utilizes at least one metal halide in the electrolyte, such that the metal of the metal halide is sufficiently strong and stable in its reduced form to be able to form an electrode. The metal halides that can be used in the reversible system include zinc halides, as element zinc is sufficiently stable to be able to form an electrode. On the other hand, the non-reversible electrochemical system does not utilize the metal halides that satisfy the above requirements. Metals of metal halides that are used in the non-reversible systems are usually unstable and strong in their reduced, elemental form to be able to form an electrode. Examples of such unstable metals and their corresponding metal halides include potassium (K) and potassium halides and sodium (Na) and sodium halides.

The metal halide electrolyte can be an aqueous electrolytic solution. The electrolyte may be an aqueous solution of at least one metal halide electrolyte compound, such as ZnCl. For example, the solution may be a 15-50% aqueous solution of ZnCl, such as a 25% solution of ZnCl. In certain embodiments, the electrolyte may contain one or more additives, which can enhance the electrical conductivity of the electrolytic solution. For example, when the electrolyte contains ZnCl, such additive can be one or more salts of sodium or potassium, such as NaCl or KCl.

FIG. 1illustrates an electrochemical system100which includes at least one electrochemical flow cell105, an electrolyte and a halogen reactant contained in a sealed container101. The sealed container101is preferably a pressure containment vessel, which is configured to maintain a pressure above one atmospheric pressure in its inner volume102. Preferably, the sealed container101is configured to maintain a pressure in its inner volume above the liquefication pressure for the halogen reactant, such as elemental chlorine. For functioning at a normal temperature such as 10-40° C., the sealed container may be configured to maintain an inside pressure of at least 75 psi or of at least 100 psi or of at least 125 psi or of at least 150 psi or of at least 175 psi or of at least 200 psi or of at least 250 psi or of at least 300 psi or of at least 350 psi or of at least 400 psi or of at least 450 psi or of at least 500 psi or of at least 550 psi or of at least 600 psi, such as 75-650 psi or 75-400 psi and all subranges described previously. The walls of the sealed container may be composed of a structural material capable to withstand the required pressure. One non-limiting example of such a material is stainless steel.

The at least one electrochemical flow cell105contained inside the sealed container101is preferably a horizontally positioned cell, which may include a horizontal positive electrode and horizontal negative electrode separated by a gap. The horizontally positioned flow cell105may be advantageous because when the circulation of the liquid stops due to, for example, turning off a discharge or a charge pump, some amount of liquid (the electrolyte and/or the halogen reactant) may remain in the reaction zone of the flow cell105. The amount of the liquid may be such that it provides electrical contact between the positive and negative electrodes of the same flow cell105. The presence of the liquid in the reaction zone may allow a faster restart of the electrochemical system when the circulation of the metal halide electrolyte and the halogen reagent is restored compared to systems that utilize a vertically positioned flow cell(s)105, while providing for shunt interruption. The presence of the electrolyte in the reaction zone may allow for the flow cell105to hold a charge in the absence of the circulation and thus, ensure that the system provides uninterrupted power supply (UPS). The horizontally positioned flow cell(s)105in a combination with a liquefied chlorine reactant used as a halogen reactant may also prevent or reduce a formation of chlorine bubbles during the operation.

In many embodiments, the sealed container may contain more than one electrochemical flow cell105. In certain embodiments, the sealed container may contain a plurality of electrochemical flow cells105, which may be connected in series. In some embodiments, the plurality of electrochemical flow cells105that are connected in series may be arranged in a stack. For example, element103inFIG. 1represents a vertical stack of horizontally positioned electrochemical flow cells105, which are connected in series. The stack of horizontally positioned flow cells105may be similar to the one disclosed on pages 7-11 and FIGS. 1-3 of WO2008/089205, which is incorporated herein by reference in its entirety. The advantages of a single horizontally positioned flow cell105apply to the stack as well.

The electrochemical system can include a feed pipe or manifold that may be configured in a normal discharge operation mode to deliver a mixture comprising the metal-halide electrolyte and the liquefied halogen reactant to the at least one flow cell105. The electrochemical system may also include a return pipe or manifold that may be configured in the discharge mode to collect products of an electrochemical reaction from the at least one electrochemical flow cell105. Such products may be a mixture comprising the metal-halide electrolyte and/or the liquefied halogen reactant, although the concentration of the halogen reactant in the mixture may be reduced compared to the mixture entering the flow cell105due to the consumption of the halogen reactant in the discharge mode.

For example, inFIG. 1a feed pipe or manifold115is configured to deliver a mixture comprising the metal-halide electrolyte and the liquefied halogen reactant to the horizontally positioned flow cells105of the stack103. A return pipe or manifold120is configured to collect products of an electrochemical reaction from flow cells105of the stack103. As will be further discussed, in some embodiments, the feed pipe or manifold and/or the return pipe or manifold may be a part of a stack assembly for the stack of the horizontally positioned flow cells105. In some embodiments, the stack103may be supported directly by walls of the vessel101. Yet in some embodiments, the stack103may be supported by one or more pipes, pillars or strings connected to walls of the vessel101and/or reservoir119.

The feed pipe or manifold and the return pipe or manifold may be connected to a reservoir119that may contain the liquefied, e.g. liquid, halogen reactant and/or the metal halide reactant. Such a reservoir may be located within the sealed container101. The reservoir, the feed pipe or manifold, the return pipe or manifold and the at least one flow cell105may form a loop circuit for circulating the metal-halide electrolyte and the liquefied halogen reactant.

The metal-halide electrolyte and the liquefied halogen reactant may flow through the loop circuit in opposite directions in charge and discharge modes. In the discharge mode, the feed pipe or manifold115may be used for delivering the metal-halide electrolyte and the liquefied halogen reactant to the at least one flow cell105from the reservoir119and the return pipe or manifold120for delivering the metal-halide electrolyte and the liquefied halogen reactant from the at least one flow cell105back to the reservoir. In the charge mode, the return pipe or manifold120may be used for delivering the metal-halide electrolyte and/or the liquefied halogen reactant to the at least one flow cell105from the reservoir119and the feed pipe or manifold115for delivering the metal-halide electrolyte and/or the liquefied halogen reactant from the at least one flow cell105back to the reservoir119.

In some embodiments, when the system utilizes a vertical stack103of horizontally positioned flow cells105, the return pipe or manifold120may be an upward-flowing return pipe or manifold. The pipe120includes an upward running section121and a downward running section122. The flow of the metal-halide electrolyte and the liquefied halogen electrolyte leaves the flow cells105of the stack103in the discharge mode upward through the section121and then goes downward to the reservoir through the section122. The upward flowing return pipe or manifold may prevent the flow from going mostly through the bottom flow cell105of the stack103, thereby, providing a more uniform flow path resistance between the flow cells105of the stack.

The electrochemical system may include one or more pumps for pumping the metal-halide electrolyte and the liquefied halogen reactant. Such a pump may or may not be located within the inner volume of the sealed vessel. For example,FIG. 1shows discharge pump123, which fluidly connects the reservoir119and the feed pipe or manifold115and which is configured to deliver the metal-halide electrolyte and the liquefied halogen reactant through the feed pipe or manifold115to the electrochemical flow cell(s)105in the discharge mode. In some embodiments, the electrochemical generation system may include charge pump depicted as element124inFIG. 1. The charge pump fluidly connects the return pipe or manifold120to the reservoir119and can be used to deliver the metal-halide electrolyte and the liquefied halogen reactant through the return pipe or manifold to the electrochemical flow cell(s)105in the charge mode. In some embodiments, the electrochemical system may include both charge and discharge pumps. The charge and discharge pumps may be configured to pump the metal-halide electrolyte and the liquefied halogen reactant in the opposite directions through the loop circuit that includes the feed pipe or manifold and the return pump or manifold. Preferably, the charge and discharge pumps are configured in such a way so that only one pump operates at a given time. Such an arrangement may improve the reliability of the system and increase the lifetime of the system. The opposite pump arrangement may also allow one not to use in the system a valve for switching between the charge and discharge modes. Such a switch valve may often cost more than an additional pump. Thus, the opposite pump arrangement may reduce the overall cost of the system.

Pumps that are used in the system may be centripetal pumps. In some embodiments, it may be preferred to use a pump that is capable to provide a pumping rate of at least 30 L/min.

FIG. 1depicts the reservoir as element119. The reservoir119may be made of a material that is inert to the halogen reactant. One non-limiting example of such an inert material may be a polymer material, such as polyvinyl chloride (PVC). The reservoir119may also store the metal halide electrolyte. In such a case, if the liquefied chlorine is used as a liquefied halogen reactant, then the chlorine can be separated from the metal halide electrolyte due to a higher density (specific gravity) of the former, and/or by a separation device as described below with respect toFIGS. 7 and 8.FIG. 1shows liquefied chlorine at the lower part of the reservoir (element126) and the metal-halide electrolyte being above the liquefied chlorine in the reservoir (element125).

The reservoir119may contain a feed line for the liquefied halogen reactant, which may supply the halogen reactant126to the feed pipe or manifold115of the system. A connection between the halogen reactant feed line and the feed manifold of the system may occur before, at or after a discharge pump123. In some embodiments, the connection between the halogen reactant feed line and the feed manifold of the system may comprise a mixing venturi.FIG. 1presents the feed line for the liquefied halogen reactant as element127. An inlet of the feed line127, such as a pipe or conduit, may extend to the lower part126of the reservoir119, where the liquefied halogen reactant, such as the liquefied chlorine reactant, may be stored. An outlet of the feed line127is connected to an inlet of the discharge pump123. The electrolyte intake feed line, such as a pipe or conduit132, may extend to the upper part125, where the metal-halide electrolyte is located.

In some embodiments, the reservoir119may include one or more sump plates, which may be, for example, a horizontal plate with holes in it. The sump plate may facilitate the settling down of the liquefied halogen reactant, such as liquefied chlorine reactant, at the lower part126of the reservoir, when the liquefied halogen reactant returns to the reservoir119, for example, from the return pipe or manifold120in the discharge mode. The reservoir119is preferably but not necessarily located below the stack103of flow cells105.

In some embodiments, the reservoir119may include one or more baffle plates. Such baffle plates may be vertical plates located at the top and bottom of the reservoir. The baffle plates may reduce and/or prevent eddy currents in the returning flow of the metal-halide electrolyte and the liquefied halogen reactant, thereby enhancing the separation of the liquefied halogen from the metal-halide electrolyte in the reservoir.

In certain embodiments, the discharge pump may be positioned with respect to the reservoir so that it's inlet/outlet is located below the upper level of the metal-halide electrolyte in the reservoir. In certain embodiments, the inlet/outlet of the discharge pump may be positioned horizontally or essentially horizontally. In such an arrangement, the flow of the metal-halide electrolyte and the liquefied halogen reactant may make a 90 degree turn in the discharge pump from a horizontal direction in the inlet to a vertical direction in the feed manifold or pipe115. In some embodiments, the inlet of the discharge pump123may include a bellmouth piece, which may slow down the flow and thereby prevent/reduce formation of turbulence in the reservoir.

The charge pump may also be positioned with it's inlet/outlet located below the upper level of the metal-halide electrolyte in the reservoir. In certain embodiments, the inlet/outlet of the charge pump may be located at a lower level than the inlet/outlet of the discharge pump. The inlet/outlet of the charge pump may also have a bellmouth piece, which may slow down the flow and thereby prevent/reduce formation of turbulence in the reservoir.

FIG. 6illustrates the reservoir119which has a lower part126, which may contain the liquefied halogen reactant, such as a liquefied molecular chlorine reactant; an upper part125, which may contain the metal halide reactant; a horizontal sump plate603, vertical baffle plates604, a horizontal inlet605of a discharge pump, a horizontal outlet606of a charge pump and a feed line607for the liquefied halogen reactant, which has an inlet in the lower part126of the reservoir and which is connected to the discharge pump's inlet605. The sump plate603is positioned approximately at the level where the boundary between the metal-halide electrolyte and the halogen reactant is expected to be located. Line608schematically depicts the upper level of the metal-halide electrolyte in the reservoir. Discharge pump's inlet605and charge pump's outlet606may protrude through the walls of the reservoir.

In some embodiments, the electrochemical system may include a controlling element, which may be used, for example, for controlling a rate of the discharge pump, a rate of the charge pump and/or a rate of feeding the halogen reactant into the electrolyte. Such a controlling element may be an analog circuit.FIG. 1depicts the controlling element as element128, which may control one or more of the following parameters: rates of the charge pump124and the discharge pump123and a feed rate of the liquefied chlorine reactant through the feed line127.

The inner volume of the sealed container may have several pressurized zones, each having a different pressure. For example, the inner volume may include a first zone, and a second zone having a pressure higher than that of the first zone. In some embodiments, the first zone may be enveloped or surrounded by the second, higher pressure zone. The first zone may contain the electrolyte/liquefied halogen reactant loop, i.e. the reservoir119, the flow cell(s)105, pump(s)123and124, manifold(s)115,120, while the second surrounding or enveloping zone may be a space between the first zone and the walls of the sealed vessel101. InFIG. 1, the flow cells105, the feed manifold or pipe115, the reservoir119, including the metal halide reactant in the upper part125of the reservoir and the liquefied halogen reactant in its lower part126, and the return manifold or pipe120all may be in the first pressure zone, while the higher pressure second zone may be represented by the areas129,130and131of the inner volume of the vessel101.

In such an arrangement, a pressure in the first zone may be a pressure sufficient to liquefy the halogen reactant at a given temperature. Such a pressure may be at least 75 psi or at least 100 psi or at least 125 psi or at least 150 psi or at least 175 psi or at least 200 psi or at least 250 psi or at least 300 psi or at least 350 psi or at least 400 psi, such as 75-450 psi or 75-400 psi and all subranges in between. At the same time, a surrounding pressure in the second pressure zone may be higher than a maximum operating pressure of the first zone. Such a surrounding pressure may be at least 75 psi or at least 100 psi or at least 125 psi or at least 150 psi or at least 175 psi or at least 200 psi or at least 250 psi or at least 300 psi or at least 350 psi or at least 400 psi or at least 450 psi or at least 500 psi or at least 550 psi or at least 600 psi, such as 75-650 psi or 200-650 psi or 400-650 psi and all the subranges in between.

The enveloped arrangement may provide a number of advantages. For example, in the event of a leak from the first zone/loop circuit, the higher pressure in the surrounding second zone may cause the leaking component(s) to flow inwards the first zone, instead of outwards. Also, the surrounding higher pressure zone may reduce/prevent fatigue crack propagation over components of the first zone/loop circuit, including components made of plastic, such as manifolds and walls of reservoir. The pressurized envelope arrangement may also allow using thinner outer wall(s) for the sealed container/vessel, which can, nevertheless, prevent deformation(s) that could negatively impact internal flow geometries for the metal-halide electrolyte and the liquefied halogen reactant. In the absence of the pressurizing second zone, thicker outer wall(s) may be required to prevent such deformation(s) due to an unsupported structure against expansive force of the internal higher pressure.

In certain embodiments, the outer walls of the sealed container/vessel may be formed by a cylindrical component and two circular end plates, one of which may be placed on the top of the cylindrical component and the other on the bottom in order to seal the vessel. The use of the pressurized envelope arrangement for such outer walls allows using thinner end plates, without exposing internal flow geometries for the metal-halide electrolyte and the liquefied halogen reactant compared to the case when the outer walls are exposed to the variable pressure generated during the operation of the system.

The second pressure zone may be filled with an inert gas, such as argon or nitrogen. In some embodiments, the second pressure zone may also contain an additional component that can neutralize a reagent, such as the halogen reactant, that is leaking from the first zone, and/or to heal walls of the first zone/loop circuit. Such an additional material may be, for example, a soda ash. Thus, spaces129,130and131may be filled with soda ash.

The electrochemical system in a pressurized envelope arrangement may be fabricated as follows. First, a sealed loop circuit for the metal halide electrolyte and the liquefied halogen reagent may be fabricated. The sealed loop circuit can be such that it is capable to maintain an inner pressure above a liquefication pressure of the liquefied halogen for a given temperature. The sealed loop circuit may include one or more of the following elements: one or more electrochemical flow cells105, a reservoir for storing the metal-halide electrolyte and the liquefied halogen reactant; a feed manifold or pipe for delivering the metal-halide electrolyte and the liquefied halogen reactant from the reservoir to the one or more flow cells105; a return manifold for delivering the metal-halide electrolyte and the liquefied halogen reactant from the one or more flow cells105back to the reservoir; and one or more pumps. After the loop circuit is fabricated, it may be placed inside a vessel or container, which may be later pressurized to a pressure, which is higher than a maximum operation pressure for a loop circuit, and sealed. The pressurization of the vessel may be performed by pumping in an inert gas, such as argon or nitrogen, and optionally, one or more additional components. When the walls of the vessel are formed by a cylindrical component and two end plates, the sealing procedure may include the end plates at the top and the bottom of the cylindrical component.

FIG. 2illustrates paths for a flow of the metal-halide electrolyte and the liquefied halogen reactant through the horizontally positioned flow cells105of the stack103, such as the stack103ofFIG. 1, in the discharge mode. The electrolyte flow28paths inFIG. 2are represented by arrows. For each of the flow cells105in the stack, the flow may proceed from a feed pipe or manifold21(element115inFIG. 1), into a distribution zone22, through a porous “chlorine” electrode23, over a metal electrode25, which may comprise a substrate, which may be, for example, a titanium substrate or a ruthenized titanium substrate, and an oxidizable metal, which may be, for example, zinc, on the substrate, to a collection zone26, through an upward return manifold27(element121inFIG. 1). The electrolyte flow28may proceed to a return pipe29(element122inFIG. 1).

In some embodiments, an element24may be placed on a bottom of metal electrode25. Yet in some other embodiments, such an element may be omitted. The purpose of the element24may be to prevent the flow of the metal-halide electrolyte from contacting the active metal electrode, when passing through a porous electrode of an adjacent flow cell105located beneath. In other words, element24prevents the electrolyte from touching one side (e.g., the bottom side) of every metal electrode25so that the metal (e.g., zinc) plates only on the opposite side (e.g., the top side) of the metal electrode25. In some cases, the element24may comprise the polymer or plastic material.

FIG. 2also shows barriers30. Each barrier30may be a part of a cell frame301discussed in a greater detail below. Barrier30may separate the positive electrode from the negative electrode of the same flow cell105. Barriers30may comprise an electrically insulating material, which can be a polymeric material, such as poly vinyl chloride (PVC).

In the configuration depicted inFIG. 2, the metal-halide electrolyte may be forced to flow down through the porous electrode and then up to leave the flow cell105. Such a down-and-up flow path may enable an electrical contact of the porous electrode and the metal electrode in each flow cell105with a pool of the metal halide electrolyte remaining in each flow cell105when the electrolyte flow stops and the feed manifold, distribution zone, collection zone, and return manifold drain. Such a contact may allow maintaining an electrical continuity in the stack103of flow cells105when the flow stops and may provide for an uninterrupted power supply (UPS) application without continuous pump operation. The down-and-up flow path within each flow cell105may also interrupt shunt currents that otherwise would occur when electrolyte flow stops. The shunt currents are not desired because they may lead to undesirable self-discharge of the energy stored in the system and an adverse non-uniform distribution of one or more active materials, such as an oxidizable metal, such as Zn, throughout the stack.

FIG. 5afurther illustrates flow paths through the stacked flow cells105using ZnCl2as an exemplary metal-halide electrolyte and Cl2 as an exemplary halogen reactant. The stack inFIG. 5aincludes a first cell521, which has a reaction zone506between a positive electrode504, e.g. porous carbon or permeable metal “chlorine” electrode, and a negative electrode502, e.g. a zinc electrode, and a second cell522, which has a reaction zone507between a positive electrode505and a negative electrode503. The negative electrode502of the cell522is electrically connected to the positive electrode505of the cell521, thereby providing electrical continuity between the cells of the stack. Each of the negative electrodes may comprise a conductive impermeable element, such as a titanium plate. Such element is shown as element508for electrode501, element509for the electrode502and element510for the electrode503.

FIG. 5aalso shows an electrode501or a terminal plate positioned over the positive electrode504of the cell521. When the cell521is the top terminal cell, the electrode501can be the terminal positive electrode of the stack. If the cell521is not the terminal cell, then the electrode501can be a negative electrode of an adjacent cell of the stack. The positive electrodes504and505are preferably porous electrodes, such as porous carbonaceous electrodes, such as carbon foam or permeable metal electrode.

The cells may be arranged in the stack in such a manner that a cell-to-cell distance may be significantly greater that a distance between positive and negative electrodes of a particular cell of the stack (an interelectrode distance). The interelectrode distance may be, for example, 0.5-5 mm such as 1-2 mm. In some embodiments, the cell-to-cell distance may be at least 3 times or at least 5 times or at least 8 times or at least 10 times, such as 3-15 times greater, than the interelectrode distance. The cell-to-cell distance may be defined as between two analogous surfaces in two adjacent cells. For example, the cell-to-cell distance may be a distance between an upper surface of the negative electrode502of the cell521and an upper surface of the negative electrode503of the cell522. The cell-to-cell distance may be 5-20 mm, such as 10-15 mm. The distance between a particular cell's positive and negative electrodes inFIG. 5ais a distance between the lower surface of the positive electrode504of the cell521and the upper surface of the negative electrode502of the same cell.

To achieve the significant difference between the cell to cell distance and the interelectrode distance in a particular cell, at least one of positive or negative electrodes may comprise one or more electrically conductive spacers, which (i) increase the cell-to-cell distance compared to the interelectrode distance, (ii) provide an electrical contact between positive and negative electrodes of adjacent cells, and (iii) create flow channels in a flow path of the electrolyte.

InFIG. 5a, the positive electrode505of the cell522has a porous part525and two conductive spacers523and524, which are electrically connected to the negative electrode502of the adjacent cell521. The conductive spacers523and524may or may not be made of a porous material. In certain embodiments, conductive spacers, such as spacers523and524, may be made of carbonaceous material, such as graphite or non-permeable metal. Similarly to the electrode505, the electrode504of the cell521contains a porous part520and two conductive spacers518and519. An electrolyte flow path526,527exists between adjacent anode and cathode electrodes of adjacent cells. The conductive spacers518,519divide the flow path526,527into flow channels as will be described below. The anode and cathode electrodes of the same cell are separated from each other by one or more insulating spacer(s) (shown inFIG. 9Bas element529) and/or by the cell frame (element301shown inFIG. 3) to create a reaction zone506,507flow path in each respective cell521,522.

In addition to the cells521and522,FIG. 5ashows a reservoir119; a feed line115, which includes a pump123; and a return manifold120, which includes an upper running part121and a part122, which is connected with the reservoir119. Together the reservoir119, the feed line115, the return manifold120, flow paths526,527and the reaction zone506,507flow paths form a closed loop (e.g. flow circle) for the metal halide electrolyte, which is illustrated as ZnCl2inFIG. 5a, and the halogen reactant (Cl2inFIG. 5a).

In the discharge mode, a mixture of the metal halide electrolyte and the liquefied halogen reactant arrives from the reservoir119in channel shaped flow paths526,527between the spacers518/519,523,524at the top of a respective positive electrode of a cell, such as electrode504for cell521and the electrode505for the cell522. The halogen reactant is reduced at the positive electrode. After the mixture penetrates through a porous part of the positive electrode (part520for the cell521and part525for the cell522), it becomes enriched with halogen anions (Cl— in the case of molecular chlorine used as the halogen reactant).

The reaction zone of the cell, such as zone506for the cell521or zone507for the cell522, is also a flow channel which does not contain a membrane or a separator configured to separate halogen anions, such as Cl—, from the metal halide electrolyte. Thus, from the positive electrode, the halogen anion enriched mixture proceeds down to the negative electrode, such as electrode502for the cell521and electrode503for the cell522. In the discharge mode, a metal of the negative electrode is oxidized forming positive ions that are released into the halogen anion enriched mixture.

For example, if the negative electrode comprises metallic Zn as shown inFIG. 5a, the metallic zinc is oxidized into zinc ions, while releasing two electrons. The electrolyte mixture, which is enriched with both halogen anions and metal cations after contacting the negative electrode, leaves the cell through a path in the cell frame (as will be described with respect toFIG. 3) and the upper running return manifold and goes back to the reservoir, where the mixture can be resupplied with a new dose of the liquefied halogen reactant. In sum, in the system illustrated inFIG. 5a, the following chemical reactions can take place in the discharge mode:
Cl2(Aq)+2e−→2Cl— (positive electrode)
Zn(s)→Zn2++2e−(negative electrode).
As the result of these reactions, 2.02 V per cell can be produced.

In the discharge mode, the electrochemical system can consume the halogen reactant and the metal constituting the negative electrode and produce an electrochemical potential. In the charge mode, the halogen reactant and the metal of the electrode may be replenished by applying a potential to the terminal electrodes of the stack. In the charge mode, the electrolyte from the reservoir moves in the direction opposite to the one of the discharge mode.

ForFIG. 5a, such opposite movement means that the electrolyte moves counterclockwise. In the charge mode, the electrolyte enters the cell, such as cell521or522, after passing through the return manifold520, at the electrode, which acts as a negative electrode in the discharge mode but as a positive electrode in the charge mode. Such electrodes inFIG. 5aare the electrode502for the cell521and electrode503for the cell522. At this electrode, the metal ions of the electrolyte may be reduced into elemental metal, which may be deposited back at the electrode. Zinc plates on top of each electrode502,503. For example, for the system inFIG. 5a, zinc ions may be reduced and deposited at the electrode502or503(Zn2++2 e−→Zn). The electrolyte then may pass upwards through a porous electrode, such as electrodes505and504inFIG. 5a, where halogen ions of the electrolyte may oxidize forming molecular halogen reactant.

For the case illustrated inFIG. 5a, chlorine ions of the metal-halide electrolyte oxidize at the electrodes505and504forming molecular chlorine. Because the system illustrated inFIG. 5ais placed under a pressure above the liquefication pressure for the halogen reactant, the halogen reactant, which is formed at the electrodes505and504, is in liquid form after the aqueous solution is saturated with dissolved chlorine.

The electrolyte leaves the cell, such as cell521or522, in a form of a mixture with the formed halogen reactant through flow paths526,527and then through the pipe or manifold115. A concentration of the metal halide electrolyte in the mixture can be lower than a concentration of the electrolyte that entered the cell from the pipe120. From the pipe115, the mixture may enter the reservoir, where it can be separated into the halogen reactant and the metal electrolyte per se using, for example, gravity and an optional sump plate, or some type of separating membrane.

FIG. 5billustrates an alternative flow configuration through the vertical stack103of electrochemical cells. In this embodiment, the electrochemical cells are inverted (i.e., placed upside down) relative to the embodiment illustrated inFIG. 5a. That is, the electrochemical cells are configured so that in discharge mode, the electrolyte flows from the bottom of each cell521,522, through flow paths526,527then through the porous parts520,525of electrodes504,505into the reaction zones506,507and then back into reservoir119. In charge mode, the electrolyte flows in the opposite direction (i.e., from reaction zones506,507down through electrodes504,505into the flow paths526,527). In this embodiment, zinc plates on the bottom of the negative metal electrodes501,502,503in charge mode. In this manner, the electrodeposited zinc layer grows in a downward direction in charge mode.

In discharge mode, zinc oxidizes and thereby dissolves from the negative metal electrodes502,503. Zinc ions, Zn2+enter the electrolyte as the zinc dissolves. Molecular chlorine is reduced at the porous electrode to form chlorine ions.

As in the previous embodiment, a reservoir119is provided at the bottom the vessel101. Also included is a discharge pump123operatively attached to the reservoir119. Electrolyte is pumped from the reservoir119via a feed pipe or manifold115to flow paths526,527between conductive spacers518/519,523/524through the porous regions502,525in electrodes504,505. The electrolyte exits the reactions zones506,507and returns to the reservoir119via a return pipe or manifold120.

In some embodiments, the multiple flow paths may merge into a lesser number of flows before reaching the return manifold or pipe. For example,FIG. 3shows that the electrolyte and the liquefied halogen reactant may leave the bottom of the cell through eight flow paths361-368. Since the flow leaves through the bottom of the cell, paths361-368do not have a direct connection to the top of the cell in the view shown inFIG. 3. Adjacent flow paths361and362,363and364,365and366,367and368merge at first-level merging nodes369-372into second-level flow paths373,374,375and376respectively. The second level flow paths further merge at two second level merging nodes377and378forming two third-level flow paths381and382, which further merge at a third-level node383, forming a single flow384, which enters the return manifold338. Each of the flow paths361-368have the same flow resistance as they have the same length and the same number of turns, which have the same radius, on its way to the return manifold.

As the result of the three levels of splitting, the flow of the metal halide electrolyte and the liquefied halogen reactant may enter the cell through eight separate paths353,354,355,356,357,358,359,360, each of which has the same flow resistance because they have the same length and the same number of turns, which have the same radius, i.e. the same geometry. The flow splitting nodes may split the flow of the electrolyte and the halogen reactant for each cell of the stack. The electrolyte and the liquefied halogen reactant may leave the cell through a multiple flow paths or through a single flow path.

In some embodiments, the multiple flow paths may merge into a lesser number of flows before reaching the return manifold or pipe. For example,FIG. 3shows that the electrolyte and the liquefied halogen reactant may leave the bottom of the cell through eight flow paths361-368. Since the flow leaves through the bottom of the cell, paths361-368do not have a direct connection to the top of the cell in the view shown inFIG. 3. Adjacent flow paths361and362,363and364,365and366,367and368merge at first-level merging nodes369-372into second-level flow paths373,374,375and376respectively. The second level flow paths further merge at four second level merging nodes377and378forming two third-level flow paths381and382, which further merge at a third-level node383, forming a single flow384, which enters the return manifold338. Each of the flow paths361-368have the same flow resistance as they have the same length and the same number of turns, which have the same radius, on its way to the return manifold.

FIG. 3illustrates an electrochemical cell that comprises a cell frame301. Such an electrochemical cell may be used to achieve the structures and flows shown inFIG. 2. The cell frame301may include a feed manifold element331, distribution channels, flow splitting nodes, spacer ledge335, flow merging nodes, collection channels, return manifold element338, and bypass conduit elements334.

In some embodiments, plural cell frames301, that are each identical or similar to the cell frame301depicted inFIG. 3, may be stacked vertically with the electrodes in place, to form the stack shown inFIG. 2. To form such a stack, the feed manifold element, such as the element331inFIG. 3, in each of the plural cells frames301may be aligned with the feed manifold element in another of the cell frames301, thereby to form a feed manifold of the system. The distribution channels and the flow splitting nodes in each of the cell frames301may be aligned with the distribution channels and the flow splitting nodes in another of the cell frames301, thereby forming a distribution zone of the system. The positive electrode (discharge mode) of each of the cells sits above or below the negative electrode (discharge mode) for each cell on the spaces ledges of the cell frames301, thereby forming alternating layers of positive electrodes and negative electrodes.

The flow merging nodes and the collection channels in each of the plural cells frames301may be aligned with the flow merging nodes and the collection channels in another of the cell frames301, thereby forming a collection zone of the system. The return manifold element, such as the element338inFIG. 3, in each of the cell frames301may be aligned with the return manifold element in another of the cell frames301, thereby forming a return manifold of the system. The bypass conduit element, such as the element334inFIG. 3, in each of the cell frames301may be aligned with the bypass conduit element in another of the cell frames301, thereby forming a bypass conduit of the system. The bypass conduit may be used for fluid flow and/or electrical wires or cables.

In some embodiments, the cell frame301may have a circular shape. Such a shape may facilitate insertion of the plural cells into a pressure containment vessel, which has a cylindrical shape, thereby reducing a production cost for the system. The frames301may comprise an electrically insulating material, which may be a polymer material, such as PVC.

The cell frame301based design may facilitate a low-loss flow with uniform distribution for the electrolyte and the halogen reactant; a bipolar electrical design; an ease of manufacture, internal bypass paths, and elements by which the operational stasis mode (described below) may be achieved.

Advantages of the cell frame301may include, but are not limited to, the flow-splitting design in the distribution zone that may include multiple order splits such as the first, second, and third order splits in the flow channels inFIG. 3, that result in multiple channels that each have the same flow resistance, because each of the channels has the same length and the number and radius of bends.FIG. 3shows eight feed channels per cell that each have the same flow resistance. This design with multiple flow splits may allow maintenance of a laminar flow through each of the multiple channels. The design may allow equal division of flow volume between the multiple channels, independent of flow velocity, uniformity of viscosity, or uniformity of density in the electrolyte.

Modes of Operation

An Off Mode may be used for storage or transportation of the electrochemical system. During the Off Mode, the metal halide electrolyte and the halogen reactant are not delivered to the cell. A small amount of the halogen reactant, which may remain in the horizontally positioned, may be reduced and combined with metal ions to form metal halide. For example, the remaining liquefied chlorine reactant may be reduced into halogen anions and combined with zinc ions to form zinc chloride.

In the off mode, the terminal electrodes of the one or more cells of the system may be connected via a shorting resistor, yielding a potential of zero volts for the cells of the system. In some embodiments, a blocking diode preferably may be used to prevent reverse current flow through the system via any external voltage sources.

During the Discharge Mode the discharge pump may be on and the mixture of the metal halide electrolyte and the halogen reactant may be circulated through the cell(s) of the system. Electrons may be released as metal cations are formed from the oxidizable metal that constitutes the negative electrode. The released electrons may be captured by the halogen reactant, thereby reducing the reactant to halogen anions and creating an electrical potential on terminal electrodes of the cell(s) of the system. The demand for power from the system may consume the halogen reactant, causing a release of an additional dose of the liquefied halogen reactant from the reservoir into the feed pipe or manifold of the system.

During the Stasis or Standby Mode, there may be little or no flow of the metal halide electrolyte and the halogen reactant. The availability of the system may be maintained via a balancing voltage. This balancing voltage may prevent a self-discharge of the system by maintaining a precise electrical potential on the cell(s) of the system to counteract the electrochemical reaction forces that can arise when there is no circulation of the metal halide electrolyte and the halogen reactant. The particular design of the cell plates disclosed may interrupt shunt currents that would otherwise flow through the feed and return manifolds, while maintaining cell-to-cell electrical continuity.

Radial Flow

FIGS. 9a-9cand10illustrate an embodiment of disk shaped electrodes suitable for use in a radial flow cell105,521,522where the electrolyte flows in a radial direction. In this embodiment, the impermeable metal cathode25and the porous or permeable anode23have substantially disk shaped configurations. In other words, the electrodes may have an exact circular cross section, such as that of cathode25shown inFIGS. 9aand9b, or slight deviation from a circular cross section, such as that of the scalloped anode23shown in these figures.

At least one central electrolyte flow conduit901extends through a central portion of the permeable electrode and through a central portion of the impermeable electrode. The flow conduit comprises a first opening in the central portion of the disk shaped permeable electrode23and a second opening in the central portion of the disk shaped impermeable electrode25, such that the first opening is aligned with the second opening. As shown inFIG. 10, the central electrolyte flow conduit901comprises a first portion comprising a sealed tube located in the reaction zone506between the first opening in the permeable electrode23and the second opening in the impermeable electrode25and a second portion comprising an open area between the central opening in the impermeable electrode25of the first adjacent cell in the stack103and the second side of the permeable electrode23. In other words, a central hole901is located in the center of both the impermeable metal cathode25and the porous anode23.

At least one peripheral electrolyte flow inlet/outlet902is located in a peripheral portion of the electrochemical cell above or below the permeable electrode23. In other words, a series of peripheral holes902are located around the periphery of the impermeable metal cathode25.

As used herein, the “central portion” of the disk shaped permeable electrode comprises an imaginary central circular area on a major surface of the disk shaped permeable electrode that is concentric with the disk shaped permeable electrode and has a radius that is less than the radius of the disk shaped permeable electrode. The “central portion” of the disk shaped impermeable electrode comprises an imaginary central circular area on a major surface of the disk shaped impermeable electrode that concentric with the disk shaped impermeable electrode and has a radius that is less than the radius of the disk shaped impermeable electrode. The “peripheral portion” of the disk shaped permeable electrode comprises an imaginary annular area surrounding the imaginary central circular area on the major surface of the disk shaped permeable electrode.

The term “radial flow”, as used herein, means a flow from an inlet in a central portion of an electrode to an outlet in a peripheral portion of the electrode, or from an inlet in a peripheral portion of an electrode to an outlet in a central portion of the electrode.

In one embodiment, the impermeable metal cathode25of one cell (e.g.,521) and the porous anode23(e.g., a permeable metal anode, such as a metal mesh or packed metal powder or a metal plate with holes) of the adjacent cell (e.g.,522) may be mechanically joined to each other using the conductive spacers518,519to form a radial electrode assembly900. The radial electrode assembly900can be made by brazing, welding or soldering at joints903along the conductive spacers518,519and the periphery of the electrodes. The fabrication of flow cell electrode assemblies900is discussed in more detail in copending application Ser. No. 12/877,884, now U.S. Pat. No. 8,202,641, titled “Metal Electrode Assembly For Flow Battery”, filed on the same date as the present application and hereby incorporated by reference in its entirety. Thus, the conductive spacers518,519described above with respect toFIGS. 5aand5bare located between the impermeable metal cathode25of one cell and the porous anode23of an adjacent cell to maintain a gap of the at least one electrolyte flow channel between the anode and the cathode. The spacers518,519, may be referred to as electrolyte flow dividers which are arranged in a radial pattern running from the central hole901to the periphery of the porous metal anode23. The conductive spacers define radially oriented electrolyte flow paths or channels526. In other words, the dividers divide the electrolyte flow channel or space between adjacent cells into a plurality of electrolyte flow channels or paths526.

The electrodes are mounted in an electrically non-conducting (i.e., insulating) cell frame301. As shown inFIG. 9d, the periphery of the annular electrically non-conducting cell frame301may comprise a lip529awhich protrudes into the circular space which houses the electrodes in the middle of the cell frame. The lip529aprovides separation between the impermeable metal cathode25and the porous anode23of the same flow cell105,521,522thereby creating the reaction zone506flow channel illustrated inFIG. 5a. In an alternative embodiment, the electrically non-conducting cell frame301does not include a lip529a. Rather, the reaction zone506is produced by incorporating at least one electrically non-conducting spacer529bbetween adjacent electrodes of the same cell. The spacers may be rail shaped spacers connected to the peripheral portion of the cell frame301. Alternatively, the lip529aand spacers529bmay be used in combination. Spring shaped, flexible conductive flow dividers518provide separation between adjacent cells. The dividers518may be rigid if desired.

In one aspect of this embodiment, the central hole901may be used as a feed manifold331and the peripheral holes902may be used as return manifolds338. In an alternative aspect, the central hole901may be used as a return manifold338while one or more of the peripheral holes902may be used as feed manifolds331. That is, the flow in the flow cells105,521,522may be reversed. In this manner, the flow cells may be operated in both charge and discharge modes.

In a non-limiting example, in charge mode, the stack103of cells is configured to provide a radial flow of the electrolyte from the at least one peripheral electrolyte flow inlet/outlet902into the reaction zone506, then from the reaction zone through the disk shaped permeable (i.e., anode) electrode23into the at least one electrolyte flow channel526between the second side of the disk shaped permeable electrode and the adjacent impermeable (i.e., cathode) electrode25of the adjacent cell, then out into the at least one central electrolyte flow conduit901. In discharge mode, the stack103is configured to provide a radial flow of the electrolyte from the at least one central electrolyte flow conduit901into the at least one electrolyte flow channel526between the second side of the disk shaped permeable electrode23and the adjacent impermeable electrode25of the adjacent cell, through the disk shaped permeable electrode23into the reaction zone506, and then from the reaction zone out through the at least one peripheral electrolyte flow inlet/outlet902. Of course, the flow direction may be reversed if desired.

As shown inFIG. 15a, in the non-limiting example of the vertical stack103of horizontal cells105,521,522, the disk shaped permeable electrode23of each cell521is located below the disk shaped impermeable electrode25aof the same cell521. In the charge mode, the electrolyte flows down from the reaction zone506flow channel between electrodes23and25a, through the disk shaped permeable electrode23into the at least one electrolyte flow channel526between electrode23and an impermeable electrode25bof the adjacent cell. In the discharge mode, the electrolyte flows from the at least one electrolyte flow channel526up through the disk shaped permeable electrode23into the reaction zone506.

FIG. 10illustrates a stack103of radial flow cells. As can be seen inFIG. 10, the stacked central holes901of the electrically non-conducting cell frames301form a central manifold while the stacked peripheral holes902of the electrically non-conducting cell frames301form multiple peripheral manifolds (i.e., holes902form a plurality of channels in the frames301).

If desired, the peripheral holes902may extend through one or both electrodes. For example, the plurality of peripheral electrolyte holes (i.e., inlet/outlets)902comprise an opening through the peripheral portion of the disk shaped impermeable electrode25(but not through electrode23) and a plurality of channels in the frame301. Other configurations may also be used.

The central manifold may be configured as a feed manifold331by pumping electrolyte with a pump123(shown inFIG. 5a) from the reservoir119to the central manifold. In this configuration, electrolyte spreads across the porous electrode23laterally as it flows out of the central manifold radially toward the return manifolds338. If the peripheral holes902are used as feed manifolds331and the central hole901is used as a return manifold338, then the electrolyte will tend to focus rather than spread as it approaches the central hole901. As illustrated inFIG. 10, a toroidal shaped peripheral manifold115/121is formed over the periphery of the stack103and in communication with the peripheral holes902to provide or collect electrolyte flowing in the holes902. Other configurations may be used.

FIG. 11illustrates another configuration for a radial flow cell105,521,522. In this embodiment, the flow cell has curved spacers/flow directors or dividers518,519which form a curved flow channel or path526. As in the previous embodiment, this embodiment has a single central hole901which can be part of a central manifold. Also as in the previous embodiment, peripheral holes902can be located at the end of the curved spacers/flow directors518,519. Alternatively, the peripheral holes902can be located between adjacent curved spacers/flow directors518,519at ends of flow channels or paths526. It should be noted that the electrolyte enters the cell on one side of a porous electrode23through hole901or902and exits on the opposite side the porous electrode. Thus, the holes901and902communicate with opposite sides of a given electrode. As electrolyte flows out of either the central hole901or the peripheral holes902, a rotational component of motion is added to the lateral and radial motion of the electrolyte to generate a spiral radial flow of the electrolyte.

FIG. 12illustrates another configuration for a radial flow cell105,521,522. In this embodiment, the flow cell includes multiple “central” holes901in the central portions of the electrodes23,25. Preferably, but not necessarily, at least one of the central holes901is located in the true center of the impermeable metal cathode25and the porous anode23. As illustrated, the flow cell includes additional four central holes901ain addition to the central hole901at the true center. The number of additional central holes901ais not limited to four, however. Alternative embodiments may have more or less additional central holes901a.

As illustrated, the present embodiment does not include spacers/flow directors518,519. In alternative embodiments, however, this embodiment may include spacers/flow directors518,519. The spacers/flow directors518,519may be either straight or curved as in the previous embodiment. Further, as in the previous embodiments, the central holes901,901aand the peripheral holes902can be configured to be either feed manifolds331or return manifolds338.

FIG. 13illustrates an embodiment of a radial flow cell105,521,522with discontinuous spacers/flow directors or dividers518,519that allow electrolyte mixing. That is, the spacers/flow directors518,519of this embodiment do not extend all the way from the central hole901to the periphery of the electrodes. Because the spacers/flow directors518,519are discontinuous, electrolyte in adjacent flow channels or paths526can mix via gaps in the spacers/flow directors518,519.

The discontinuous spacers/flow directors518,519illustrated inFIG. 13are curved. As discussed above, the curve shape adds a rotational component to the electrolyte motion. In an alternative embodiment, the discontinuous spacers/flow directors518,519are straight. Further, as illustrated, the peripheral holes902are substantially wedge shaped. In other words, holes902comprise directional peripheral electrolyte inlet/outlets which protrude at a non-zero angle from a plurality of channels in the frame301. The substantially wedge shape of the peripheral holes902may provide a more effective electrolyte delivery or removal for the electrode configuration of this embodiment. The shape of the peripheral holes902, however, is arbitrary.

FIG. 14is a schematic illustration of an embodiment of a radial flow cell with a single central inlet/outlet901and multiple slot shaped peripheral inlet/outlets902. The slot shaped peripheral inlet/outlets902may extend substantially from one spacer/flow director518,519to adjacent spacer/flow director518,519defining the wide end of the wedge shaped flow path526. As illustrated inFIG. 14, a single slot shaped peripheral inlet/outlet902is provided for each flow path526. Alternatively, however, multiple slot shaped peripheral inlet/outlets902may be provided within one or more of the flow paths526.

Fluid Bypass Opening

FIG. 15billustrates a side cross section view of an embodiment of a flow cell with a fluid bypass opening1501. The cell may have polygonal or disk shaped electrodes of the prior embodiments. The inventors have discovered that flow cell designs without a bypass opening schematically shown inFIG. 15amay result in a stagnant flow zone1502at the end of the flow path526adjacent to the cell frame301. Electrolyte flows out of the feed manifold331through in paths353-360and into the flow path or channel526between electrodes23and25bof adjacent cells. InFIG. 15a, all of the electrolyte must flow from channel526through the porous electrode23into the reaction zone506flow channel between electrodes23and25aof the cell, and then exit the flow cell via outlet paths361-368to the return manifold338. The hydrodynamics of the flow cell, however, result in the formation of a stagnant zone1502adjacent to the cell frame301at the exit end of the flow path526, where the electrolyte does not flow through electrode23.

The inventors have discovered that the hydrodynamics of the flow cell may be improved with the addition of a fluid bypass opening1501in the cell frame301. The fluid bypass opening1501is an opening through the cell frame from flow channel526or reaction zone flow channel506into the return manifold338. The opening1501is configured to allow a portion of the electrolyte, such as 0-100%, for example 10-20% by volume, to flow directly from the flow path or channel526to the return manifold338without passing through the porous electrode23. In this way, the stagnant zone1502can be eliminated, yet the majority of the electrolyte (e.g., at least 80%) flows through the porous electrode23. The overall result is a flow cell with improved performance. If desired, the flow channel526may be is tapered (i.e., gradually narrowed) adjacent to at least one bypass opening to further reduce or eliminate the stagnant zone.

Separation Device

FIG. 7illustrates another embodiment of the reservoir119which has a separation device703. The reservoir119of the embodiment ofFIG. 7may be used with the system and method of any of the embodiments described above. The baffle plates604of the embodiment ofFIG. 6are optional and are not shown in the bottom portion of the reservoir119for clarity. The separation device703can be, for example, a molecular sieve, a selective membrane, or other device that is capable of separating one component of the electrolyte mixture from other components of the electrolyte, thereby facilitating modes of operation (e.g., charge and discharge) of the flow battery. The separation device703, having an appropriate geometry and properties for separating the desired components, is preferably disposed in the reservoir119between the inlet to the feed line607and the pump inlets/outlets605and606to separate the electrolyte mixture in reservoir119into two volumes705,707during the flow battery operation. A halogen content or concentration gradient that is provided by the separation device is desirable for both the chloride ions and the liquid chlorine type of halogen reactant.

The first volume705is provided for selective electrolyte component accumulation and the second volume707is provided for selective liquefied halogen (such as aqueous chlorine) accumulation. The second volume707can be located below the first volume, thereby taking advantage of the liquefied halogen having a higher density than the remaining electrolyte components. Thus, the halogen permeation from volume705into volume707may be assisted by gravity. However, depending on the type and operation of separation device703and the particular electrolyte and halogen components, volume707may be located above or to the side of volume705. An appropriate molecular sieve or membrane703can selectively allow desired molecules to pass there through. The selectivity can be based on, for example, a molecular size, and/or an electrical charge of a component.

The permeability of the molecular sieve or membrane can be variable as a function of parameters such as pressure, temperature, chemical concentration, etc. One example of a molecular sieve comprises a mesoporous carbon membrane that provides size-based selectivity of molecules that can diffuse therethrough. Larger molecules are more difficult to penetrate the pores. This provides a higher permeability to the liquefied halogen reactant (e.g., aqueous chlorine) than the metal-halide electrolyte component (e.g., zinc chloride). In addition, the separation device can further comprise a device configured to apply an electric field over the membrane or the molecular sieve. An externally applied electric field can facilitate molecular diffusion through the membrane and aid the electrical-charge-based selective diffusion.

Depending on the specific liquefied halogen and the metal halide electrolyte used, the molecular sieves can be selected to have pore sizes suitable for passing predetermined molecules. Some examples of molecular sieves are described, for example, in U.S. Pat. No. 3,939,118. The molecular sieves can include granular natural or synthetic silica-alumina materials which can have lattice structures of the zeolite type (see, e.g., the monograph Molekularsiebe (Molecular Sieves) by O. Grubner, P. Jiro and M. Ralek, VEB-Verlag der Wissenschaften, Berlin 1968), with pore widths of 2to 10(e.g., zeolite powder or bead sieves, such as Grace Davison SYLOSIV® brand powders), silica gel with pore widths of 40to 100, which are optionally absorbed in glass beads, and modified borosilicate glasses according to W. Haller (J. Chem. Phys. 42, 686 (1965)) with pore widths between 75and 2,400. Molecular sieves based on organic products may also be used. These products include 3-dimensionally crosslinked polysaccharides such as dextran gels (Sephadex grades, a product marketed by GE Healthcare Life Sciences), which can optionally be alkylated (Sephadex-LH grades, a product marketed by GE Healthcare Life Sciences), agarose gels (Sepharose, a product marketed by GE Healthcare Life Sciences), cellulose gels and agar gels. Other examples of synthetic organic gels include crosslinked polyacrylamides and polyethylene oxides crosslinked via acrylate groups (trade name Merckogel OR). Ion exchange gels such as three-dimensionally crosslinked polystyrenes provided with sulphonic acid groups and the dextran gels already mentioned above, where they possess the acid groups or ammonium groups required for ion exchange (dextran gel ion exchangers), may also be used.

The separation device can include a porous container or a tray that holds the membrane or the molecular sieve materials. The molecular sieve materials could be in granular or powder form. The container can include electrodes or conductive plates for applying an electric field to the membrane or the molecular sieve materials. A voltage can be applied to the electrodes or conductive plates from a voltage output of the flow battery, or from a different power source (e.g., grid power, small battery located inside or outside the flow battery vessel101, etc.). The voltage applied to the separation device facilitates the selective diffusion of the liquefied halogen reactant through the separation device. The separation device can be permanently coupled (e.g., welded, glued, etc.) or removably coupled (e.g., bolted, clamped, etc.) to a wall of the reservoir119. Alternatively, only the granular molecular sieve materials or the membrane may be removable from the porous container or tray, while the container or tray may be permanently coupled to the wall of the reservoir.

It should be noted that the first volume705does not have to exclusively contain only the remaining electrolyte components and that the second volume707does not have to exclusively contain only the liquefied halogen (such as aqueous chlorine). A substantial concentration difference of halogen reactant or remaining electrolyte components across the separation device703is sufficient. Thus, the first volume705may contain the liquefied halogen in addition to the remaining electrolyte components and the second volume707may contain the remaining electrolyte components in addition to the liquefied halogen, as long as there is a higher liquefied halogen concentration in volume707than in volume705, and/or as long as there is a higher remaining electrolyte components concentration in volume705than in volume707. The concentration difference can be, for example, an at least 10% difference in concentration of the halogen reactant between the first and second volumes, such as an at least 50% difference, such as an at least 100% difference, such as an at least 200% difference, for example a 10-500% difference. The separation device703can be selected (e.g., a specific pore size may be selected) and/or operated (e.g., by applying a particular voltage) to provide the desired concentration difference.

In the discharge mode of flow battery operation illustrated inFIG. 7, the feed line607has an inlet in the second volume707of the reservoir119below the separation device703, and feeds fluid with a higher concentration of halogen reactant (i.e., the fluid with a higher concentration of desired elements for discharge flow function) from volume707into the flow loop. The inlet605of the discharge pump intakes the fluid from the first volume705, which has a higher concentration of the remaining electrolyte components than volume707. Optionally, the inlet605of the discharge pump may be omitted or may remain inoperative during discharge mode if sufficient electrolyte is present in the second volume707. The electrolyte and the liquid halogen are mixed in the flow loop and after flowing through the cells and undergoing reactions therein, the fluid mixture is discharged back into the reservoir119. Preferably, the mixture is discharged into the first volume705from charge pump inlet/outlet606. However, a different, separate outlet may be used to discharge the mixture into volume705from the flow loop. Unused halogen reactant selectively or preferentially permeates through the separation device703(i.e., halogen reactant permeates through device703at a higher rate than the remaining electrolyte components) and selectively or preferentially accumulates in the second volume707. Other electrolyte components have a lower permeability through the separation device703than the halogen and preferentially remain in the first volume705. A concentration difference described above is thus established and maintained with the help of the separation device703.

In the charge mode illustrated inFIG. 8, the remaining electrolyte components in the first volume705are fed into the flow loop by the charge pump inlet606located in the first volume705above the separation device703. The concentrated halogen in the second volume707is preferably excluded or minimized from being taken into the flow loop. After flowing through the cells and undergoing reactions therein, the fluid is discharged back into the reservoir119. Preferably, the fluid is discharged from the discharge pump inlet/outlet605into the first volume705. However, a different, separate outlet may be used to discharge the fluid into volume705from the flow loop. The discharged fluid is separated by the separation device703, the halogen reactant selectively permeates into the second volume707, leaving a higher concentration of the electrolyte component(s) in the first volume705than in the second volume707.

Advantageously, the separation device enables an architecture with simplified single flow loop plumbing, valving, pump layout, etc. Alternative flow battery designs typically require two independent flow systems which are more complicated, more costly, and are more prone to cross leakage, etc.

Although the foregoing refers to particular preferred embodiments, it will be understood that the invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.