WO2011011533A2

WO2011011533A2 - Electrochemical system having a device for separating reactants

Info

Publication number: WO2011011533A2
Application number: PCT/US2010/042774
Authority: WO
Inventors: Rick Winter; Jonathan L. Hall; Gerardo Jose La O'; Thomas Stepien
Original assignee: Primus Power Corporation
Priority date: 2009-07-24
Filing date: 2010-07-21
Publication date: 2011-01-27
Also published as: WO2011011533A3; TWI491094B; TW201112468A

Abstract

An electrochemical system, such as a flow battery, includes a vessel. The vessel contains: (a) at least one cell that includes a first electrode, a second electrode, and a reaction zone between the first and second electrodes, (b) a reservoir containing a first volume configured to selectively accumulate metal-halide electrolyte component and a second volume configured to selectively accumulate a liquefied halogen reactant, (c) a separation device separating the first volume from the second volume, and (d) a flow circuit configured to deliver the halogen reactant and the metal-halide electrolyte between the reservoir and the at least one cell.

Description

ELECTROCHEMICAL SYSTEM HAVING A DEVICE FOR

SEPARATING REACTANTS

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims benefit of U.S. patent application serial number 12/458,853, filed on July 24, 2009 and U.S. provisional patent application serial number 61/364,631 filed on July 15, 2010, both of which are incorporated herein by reference in their entirety.

FIELD

[0002] The present invention is directed to electrochemical systems, such as flow batteries, and methods of using same.

BACKGROUND

[0003] 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.

[0004] 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.

[0005] Such electrochemical energy systems are described in, for example, U.S. Patent 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

[0006] In one embodiment, an electrochemical system, such as a flow battery, includes a vessel. The vessel contains: (a) at least one cell that includes a first electrode, a second electrode, and a reaction zone between the first and second electrodes, (b) a reservoir containing a first volume configured to selectively accumulate metal-halide electrolyte component and a second volume configured to selectively accumulate a liquefied halogen reactant, (c) a separation device separating the first volume from the second volume, and (d) a flow circuit configured to deliver the halogen reactant and the metal-halide electrolyte between the reservoir and the at least one cell.

[0007] In a preferred embodiment, the separation device comprises a molecular sieve or a selective porous membrane.

[0008] In another embodiment, a method of operating an electrochemical system, includes: providing a system comprising a vessel which contains (a) at least one cell that comprises a first electrode, a second electrode, and a reaction zone between the first and second electrodes; and (b) a reservoir containing a first volume and a second volume separated by a separation device. The method further includes mixing a metal-halide electrolyte component from the first volume and a liquefied halogen reactant from the second volume to form an electrolyte mixture; providing the electrolyte mixture to the at least one cell in a discharge mode to generate electricity; and returning the electrolyte mixture from the at least one cell to the first volume in the reservoir, such that the unused liquefied halogen reactant from the returned electrolyte mixture permeates from the first volume through the separation device to the second volume.

[0009] Yet in another embodiment, the method further includes providing the metal-halide electrolyte component from the first volume to the at least one cell in a charge mode to charge the electrochemical system; and returning the electrolyte from the at least one cell to the first volume in the reservoir, such that the any liquefied halogen reactant in the returned electrolyte permeates from the first volume through the separation device to the second volume.

[0010] In another embodiment, the separation device comprises a sump plate, such as a flat sump plate or a curved sheet with at least two openings.

[0011] In one configuration, the separation device is a substantially truncated cone or funnel shaped sheet. A truncated cone or funnel shaped separator has a circular or oval horizontal cross sectional shape and an opening on the first end having a larger size than an opening on the opposite second end. The truncated cone shape may have a steady increase in cross sectional size from the second to the first end and a relatively constantly sloped sidewall. A funnel shape may have a non-steady increase (i.e., a jump) in cross sectional size from the second to the first end and one or more curves in the sloped sidewall.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 illustrates a side cross section view of an embodiment of the electrochemical system with a sealed container containing a stack of electrochemical cells.

[0013] FIG. 2 illustrates a side cross section view of flow paths in a stack of horizontally positioned cells.

[0014] FIG. 3 illustrates a three dimensional view of cell frames that can be used in certain embodiments of the electrochemical system.

[0015] FIG. 4 is a prior art phase diagram for a molecular chlorine as presented in U.S. patent no. 3,940,283.

[0016] FIG. 5 schematically illustrates a three dimensional view of flow paths in the electrochemical system in a discharge mode.

[0017] FIG. 6 schematically illustrates a side cross-sectional view of a reservoir which has a sump plate separation device and baffle plates.

[0018] FIG. 7 schematically illustrates a side cross-sectional view of a reservoir which has a separation device in a discharge operation of the electrochemical system.

[0019] FIG. 8 schematically illustrates a side cross-sectional view of a reservoir which has a separation device in a charge operation of the electrochemical system.

[0020] FIG. 9 illustrates a three dimensional cut-out view of a reservoir having a separation device disposed therein in accordance with one embodiment of the invention.

[0021] FIG. 10 illustrates a three dimensional cut-out view of a reservoir having a separation device disposed therein in accordance with another embodiment of the invention. DETAILED DESCRIPTION

[0022] The following document, the disclosure of which is incorporated herein by reference in its entirety, can be useful for understanding and practicing the embodiments described herein: U.S. Pat. Application Ser. No. 12/523,146.

[0023] 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.

[0024] 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.

[0025] 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, Figure 4 presents 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. [0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] 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.

[0031] 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. [0032] 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.

[0033] 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. In such a case, the electrochemical system may function as a reversible system.

[0034] 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 nonreversible 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.

[0035] 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. [0036] Figure 1 illustrates an electrochemical system 100 which includes at least one electrochemical cell, an electrolyte and a halogen reactant contained in a sealed container 101. The sealed container 101 is preferably a pressure containment vessel, which is configured to maintain a pressure above one atmospheric pressure in its inner volume 102. Preferably, the sealed container 101 is 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 10-40⁰C, 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.

[0037] The at least one electrochemical cell contained inside the sealed container 101 is preferably a horizontally positioned cell, which may include a horizontal positive electrode and horizontal negative electrode separated by a gap. The horizontally positioned cell may 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 cell. The amount of the liquid may be such that it provides electrical contact between the positive and negative electrodes of the same cell. 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 cell(s), while providing for shunt interruption. The presence of the electrolyte in the reaction zone may allow for the cell to hold a charge in the absence of the circulation and thus, ensure that the system provides uninterrupted power supply (UPS). The horizontally positioned cell(s) in 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.

[0038] In many embodiments, the sealed container may contain more than one

electrochemical cell. In certain embodiments, the sealed container may contain a plurality of electrochemical cells, which may be connected in series. In some embodiments, the plurality of electrochemical cells that are connected in series may be arranged in a stack. For example, element 103 in Figure 1 represents a vertical stack of horizontally positioned electrochemical cells, which are connected in series. The stack of horizontally positioned cells may be similar to the one disclosed on pages 7-11 and Figures 1-3 of WO2008/089205, which is

incorporated herein by reference in its entirety. The advantages of a single horizontally positioned cell apply to the stack as well.

[0039] 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 cell. 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 cell. 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 cell due to the consumption of the halogen reactant in the discharge mode.

[0040] For example, in Figure 1 a feed pipe or manifold 115 is configured to deliver a mixture comprising the metal-halide electrolyte and the liquefied halogen reactant to the horizontally positioned cells of the stack 103. A return pipe or manifold 120 is configured to collect products of an electrochemical reaction from cells of the stack. 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 cells. In some embodiments, the stack 103 may be supported directly by walls of the vessel 101. Yet in some embodiments, the stack 103 may be supported by one or more pipes, pillars or strings connected to walls of the vessel 101 and/or reservoir 119.

[0041] The feed pipe or manifold and the return pipe or manifold may be connected to a reservoir 119 that may contain the liquefied, e.g. liquid, halogen reactant and/or the metal halide reactant. Such a reservoir may be located within the sealed container 101. The reservoir, the feed pipe or manifold, the return pipe or manifold and the at least one cell may form a loop circuit for circulating the metal-halide electrolyte and the liquefied halogen reactant.

[0042] 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 manifold 115 may be used for delivering the metal-halide electrolyte and the liquefied halogen reactant to the at least one cell 103 from the reservoir 119 and the return pipe or manifold 120 for delivering the metal-halide electrolyte and the liquefied halogen reactant from the at least one cell back to the reservoir. In the charge mode, the return pipe or manifold 120 may be used for delivering the metal-halide electrolyte and/or the liquefied halogen reactant to the at least one cell 103 from the reservoir 119 and the feed pipe or manifold 115 for delivering the metal-halide electrolyte and/or the liquefied halogen reactant from the at least one cell 103 back to the reservoir 119.

[0043] In some embodiments, when the system utilizes a vertical stack of horizontally positioned cells, the return pipe or manifold 120 may be an upward-flowing return pipe or manifold. The pipe 120 includes an upward running section 121 and a downward running section 122. The flow of the metal-halide electrolyte and the liquefied halogen electrolyte leaves the cells of the stack 103 in the discharge mode upward through the section 121 and then goes downward to the reservoir through the section 122. The upward flowing return pipe or manifold may prevent the flow from going mostly through the bottom cell of the stack 103, thereby, providing a more uniform flow path resistance between the cells of the stack.

[0044] 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, Figure 1 shows discharge pump 123, which fluidly connects the reservoir 119 and the feed pipe or manifold 115 and which is configured to deliver the metal-halide electrolyte and the liquefied halogen reactant through the feed pipe or manifold 115 to the electrochemical cell(s) 103 in the discharge mode. In some embodiments, the electrochemical generation system may include charge pump depicted as element 124 in Figure 1. The charge pump fluidly connects the return pipe or manifold 120 to the reservoir 119 and can be used to deliver the metal-halide electrolyte and the liquefied halogen reactant through the return pipe or manifold to the electrochemical cell(s) in 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.

[0045] 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.

[0046] Figure 1 depicts the reservoir as element 119. The reservoir 119 may 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 reservoir 119 may 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 to Figs. 7 and 8. Figure 1 shows liquefied chlorine at the lower part of the reservoir (element 126) and the metal-halide electrolyte being above the liquefied chlorine in the reservoir (element 125).

[0047] The reservoir 119 may contain a feed line for the liquefied halogen reactant, which may supply the halogen reactant 126 to the feed pipe or manifold 115 of 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 pump 123. In some embodiments, the connection between the halogen reactant feed line and the feed manifold of the system may comprise a mixing venturi. Figure 1 presents the feed line for the liquefied halogen reactant as element 127. An inlet of the feed line 127, such as a pipe or conduit, may extend to the lower part 126 of the reservoir 119, where the liquefied halogen reactant, such as the liquefied chlorine reactant, may be stored. An outlet of the feed line 127 is connected to an inlet of the discharge pump 123. The electrolyte intake feed line, such as a pipe or conduit 132, may extend to the upper part 125, where the metal-halide electrolyte is located.

[0048] In some embodiments, the reservoir 119 may 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 part 126 of the reservoir, when the liquefied halogen reactant returns to the reservoir 119, for example, from the return pipe or manifold 120 in the discharge mode. The reservoir 119 is preferably but not necessarily located below the stack of cells 103.

[0049] In some embodiments, the reservoir 119 may 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.

[0050] 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 pipe 115. In some embodiments, the inlet of the discharge pump 123 may include a bellmouth piece, which may slow down the flow and thereby prevent/reduce formation of turbulence in the reservoir.

[0051] 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.

[0052] Figure 6 illustrates the reservoir 119 which has a lower part 126, which may contain the liquefied halogen reactant, such as a liquefied molecular chlorine reactant; an upper part 125, which may contain the metal halide reactant; a separation device, such as a horizontal sump plate 603, vertical baffle plates 604, a horizontal inlet 605 of a discharge pump, a horizontal outlet 606 of a charge pump and a feed line 607 for the liquefied halogen reactant, which has an inlet in the lower part 126 of the reservoir and which is connected to the discharge pump's inlet 605. The sump plate 603 is positioned approximately at the level where the boundary between the metal-halide electrolyte and the halogen reactant is expected to be located. Line 608 schematically depicts the upper level of the metal-halide electrolyte in the reservoir. Discharge pump's inlet 605 and charge pump's outlet 606 may protrude through the walls of the reservoir.

[0053] 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. Figure 1 depicts the controlling element as element 128, which may control one or more of the following parameters: rates of the charge pump 124 and the discharge pump 123 and a feed rate of the liquefied chlorine reactant through the feed line 127.

[0054] 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 reservoir 119, the cell(s) 103, pump(s) 123 and 124, 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 vessel 101. In Figure 1, the cells 103, the feed manifold or pipe 115, the reservoir 119, including the metal halide reactant in the upper part 125 of the reservoir and the liquefied halogen reactant in its lower part 126, and the return manifold or pipe 120 all may be in the first pressure zone, while the higher pressure second zone may be represented by the areas 129, 130 and 131 of the inner volume of the vessel 101.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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, spaces 129, 130 and 131 may be filled with soda ash.

[0059] 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 cells, 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 cells; a return manifold for delivering the metal-halide electrolyte and the liquefied halogen reactant from the one or more cells back 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.

[0060] Figure 2 illustrates paths for a flow of the metal-halide electrolyte and the liquefied halogen reactant through the horizontally positioned cells of the stack, such as the stack 103 of Figure 1, in the discharge mode. The electrolyte flow paths in Figure 2 are represented by arrows. For each of the cells in the stack, the flow may proceed from a feed pipe or manifold 21 (element 115 in Figure 1), into a distribution zone 22, through a porous "chlorine" electrode 23, over a metal electrode 25, 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 zone 26, through an upward return manifold 27 (element 121 in Figure 1), and to a return pipe 29 (element 122 in Figure

1).

[0061] In some embodiments, an element 24 may be placed on a bottom of metal electrode 25. Yet in some other embodiments, such an element may be omitted. The purpose of the element 24 may 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 cell located beneath. In some cases, the element 24 may comprise the polymer or plastic material.

[0062] Figure 2 also shows barriers 30. Each barrier 30 may be a part of a cell frame discussed in a greater detail below. Barrier 30 may separate the positive electrode from the negative electrode of the same cell. Barriers 30 may comprise an electrically insulating material, which can be a polymeric material, such as poly vinyl chloride (PVC).

[0063] In the configuration depicted in Figure 2, the metal-halide electrolyte may be forced to flow down through the porous electrode and then up to leave the cell. Such a down- and-up flow path may enable an electrical contact of the porous electrode and the metal electrode in each cell with a pool of the metal halide electrolyte remaining in each cell when 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 stack of cells when 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 cell may 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.

[0064] Figure 5 further illustrates flow paths through the stacked cells using ZnCl₂ as an exemplary metal-halide electrolyte and Cl₂ as an exemplary halogen reactant. The stack in Figure 5 includes a cell 521, which has a reaction zone 506 between a positive electrode 504, e.g. porous carbon "chlorine" electrode, and a negative electrode 502, e.g. zinc electrode, and a cell 522, which has a reaction zone 507 between a positive electrode 505 and a negative electrode 503. The negative electrode 502 of the cell 522 is electrically connected to the positive electrode 505 of the cell 521, thereby providing electrical continuity between the cells of the stack. Each of the negative electrodes may comprise a conductive impermeable element, which is similar to the element 24 in Figure 2. Such element is shown as element 509 for the electrode 502 and element 510 for the electrode 503.

[0065] Figure 5 also shows an electrode 501 or a terminal plate positioned over the positive electrode 504 of the cell 521. When the cell 521 is the top terminal cell, the electrode 501 can be the terminal positive electrode of the stack. If the cell 521 is not the terminal cell, then the electrode 521 can be a negative electrode of an adjacent cell of the stack. The positive electrodes 504 and 505 are preferably porous electrodes, such as porous carbonaceous electrodes, such as carbon foam electrode.

[0066] 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 electrode 502 of the cell 521 and an upper surface of the negative electrode 503 of the cell 522. 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 in Figure 5 is a distance between the lower surface of the positive electrode 504 of the cell 521 and the upper surface of the negative electrode 502 of the same cell.

[0067] 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 and (ii) provide a electrical contact between positive and negative electrodes of adjacent cells.

[0068] In Figure 5, the positive electrode 505 of the cell 522 has a porous part 525 and two conductive spacers 523 and 524, which are electrically connected to the negative electrode 502 of the adjacent cell 521. The conductive spacers 523 and 524 may or may not be made of a porous material. In certain embodiments, conductive spacers, such as spacers 523 and 524, may be made of carbonaceous material, such as graphite. Similarly to the electrode 505, the electrode 504 of the cell 521 contains a porous part 520 and two conductive spacers 518 and 519.

[0069] In addition to the cells 521 and 522, Figure 5 shows a reservoir 119; a feed line

115, which includes a pump 123; and a return manifold 120, which includes an upper running part 121 and a part 122, which is connected with the reservoir 119. Together the reservoir

119, the feed line 115, the return manifold 120 and the reaction zones 506 and 507 form a closed loop (e.g. flow circle) for the metal halide electrolyte, which is illustrated as ZnCl₂ in

Figure 5, and the halogen reactant (Cl₂ in Figure 5).

[0070] In the discharge mode, a mixture of the metal halide electrolyte and the liquefied halogen reactant arrives from the reservoir 119 at the top of a respective positive electrode of a cell, such as electrode 504 for cell 521 and the electrode 505 for the cell 522. The halogen reactant is reduced at the positive electrode. After the mixture penetrates through a porous part of the positive electrode (part 520 for the cell 521 and part 525 for the cell 522), it becomes enriched with halogen anions (Cl^" in the case of molecular chlorine used as the halogen reactant).

[0071] The reaction zone of the cell, such as zone 506 for the cell 521 or zone 507 for the cell 522, does not contain a membrane or a separator configured to separate halogen anions, such as CI^", from the metal halide electrolyte. Thus, from the positive electrode, the halogen anion enriched mixture proceeds down to the negative electrode, such as electrode 502 for the cell 521 and electrode 503 for the cell 522. In the discharge mode, a metal of the negative electrode is oxidized forming positive ions that are released into the halogen anion enriched mixture.

[0072] For example, if the negative electrode comprises metallic Zn as shown in Figure 5, 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 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 in Figure 5, the following chemical reactions can take place in the discharge mode:

Cl₂(A_q) + 2e^~ -> 2Cl^" (positive electrode)

Zn_(s) -> Zn ⁺ + 2e^~ (negative electrode).

As the result of these reactions, 2.02 V per cell can be produced. [0073] 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.

[0074] For Figure 5, such opposite movement means that the electrolyte moves

counterclockwise. In the charge mode, the electrolyte enters the cell, such as cell 521 or 522, after passing through the return manifold 520, at the electrode, which acts as a negative electrode in the discharge mode but as a positive electrode in the charge mode. Such electrodes in Figure 5 are the electrode 502 for the cell 521 and electrode 503 for the cell 522. At this electrode, the metal ions of the electrolyte may be reduced into elemental metal, which may be deposited back at the electrode. For example, for the system in Figure 5, zinc ions may be reduced and deposited at the electrode 502 or 503 (Zn²⁺ + 2 e^" -> Zn). The electrolyte then may pass through a porous electrode, such as electrodes 505 and 504 in Figure 5, where halogen ions of the electrolyte may oxidize forming molecular halogen reactant.

[0075] For the case illustrated in Figure 5, chlorine ions of the metal-halide electrolyte oxidize at the electrodes 505 and 504 forming molecular chlorine. Because the system illustrated in Figure 5 is placed under a pressure above the liquefication pressure for the halogen reactant, the halogen reactant, which is formed at the electrodes 505 and 504, is in liquid form. The electrolyte leaves the cell, such as cell 521 or 522, in a form of a mixture with the formed halogen reactant through the pipe or manifold 115. 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 pipe 120. From the pipe 115, 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.

[0076] Before being delivered to the cells, the metal halide electrolyte mixed with the liquefied halogen reactant may undergo one or more flow splits, which may result in multiple flow paths to the porous electrode. These flow paths may have the same flow resistance. Each of the one or more splits may divide the flow into two. For example, Figure 3 illustrates one possible cell design that has a first level splitting node 340, which splits the flow of the metal halide electrolyte and the liquefied halogen reactant, which is provided through the feed manifold 331, into subflows 341 and 342. Each of the subflows 341 and 342 may further split into two next level subflows at second level splitting nodes 343 and 344 respectively. Each of the four subflows 345, 346, 347, and 348, that are formed at the second level nodes, further split into two third level subflows at third level nodes 349, 350, 351 and 352 respectively.

[0077] 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 paths 353, 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.

[0078] The electrolyte and the liquefied halogen reactant may leave the cell through a multiple flow paths or through a single flow path.

[0079] In some embodiments, the multiple flow paths may merge into a lesser number of flows before reaching the return manifold or pipe. For example, Figure 3 shows that the electrolyte and the liquefied halogen reactant may leave the cell through eight flow paths 361-368. Adjacent flow paths 361 and 362, 363 and 364, 365 and 366, 367 and 368 merge at first-level merging nodes 369-372 into second-level flow paths 373, 374, 375 and 376 respectively. The second level flow paths further merge at four second level merging nodes 377 and 378 forming two third- level flow paths 381 and 382, which further merge at a third- level node 383, forming a single flow 384, which enters the return manifold 338. Each of the flow paths 361-368 have 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.

[0080] Figure 3 illustrates an electrochemical cell that comprises a cell frame. Such an electrochemical cell may be used to achieve the structures and flows shown in Figure 2. The cell frame may include a feed manifold element 331, distribution channels, flow splitting nodes, spacer ledge 335, flow merging nodes, collection channels, return manifold element 338, and bypass conduit elements 334.

[0081] In some embodiments, plural cell frames, that are each identical or similar to the frame depicted in Figure 3, may be stacked vertically with the electrodes in place, to form the stack shown in Figure 2. To form such a stack, the feed manifold element, such as the element 331 in Figure 3, in each of the plural cells frames may be aligned with the feed manifold element in another of the cell frames, thereby to form a feed manifold of the system. The distribution channels and the flow splitting nodes in each of the cell frames may be aligned with the distribution channels and the flow splitting nodes in another of the cell frames, 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 frames, thereby forming alternating layers of positive electrodes and negative electrodes.

[0082] The flow merging nodes and the collection channels in each of the plural cells frames may be aligned with the flow merging nodes and the collection channels in another of the cell frames, thereby forming a collection zone of the system. The return manifold element, such as the element 338 in Figure 3, in each of the cell frames may be aligned with the return manifold element in another of the cell frames, thereby forming a return manifold of the system. The bypass conduit element, such as the element 334 in Figure 3, in each of the cell frames may be aligned with the bypass conduit element in another of the cell frames, thereby forming a bypass conduit of the system. The bypass conduit may be used for fluid flow and/or electrical wires or cables.

[0083] In some embodiments, the cell frame may 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 frames may comprise an electrically insulating material, which may be a polymer material, such as PVC.

[0084] The cell frame based 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.

[0085] Advantages of the cell frame may 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 in Figure 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. Figure 3 shows 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

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

First Embodiment of the Separation Device

[0090] Figure 6 illustrates a first embodiment of the reservoir 119 which has a separation device 603. In this embodiment, the separation device comprises the sump plate 603 which is shown in Figure 6 and described above. The sump plate 603 is preferably a flat plate with openings which separates the heavier and lighter components of the electrolyte mechanically and/or using gravity.

Second Embodiment of the Separation Device

[0091] Figure 7 illustrates another embodiment of the reservoir 119 which has a separation device 703. The reservoir 119 of the embodiment of Figure 7 may be used with the system and method of any of the embodiments described above. The baffle plates 604 are optional and are not shown in the bottom portion of the reservoir 119. The separation device 703 can 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 device 703, having an appropriate geometry and properties for separating the desired components, is preferably disposed in the reservoir 119 between the inlet to the feed line 607 and the pump inlets/outlets 605 and 606 to separate the electrolyte mixture in reservoir 119 into two volumes 705, 707 during the flow battery operation.

[0092] The first volume 705 is provided for selective electrolyte component accumulation and the second volume 707 is provided for selective liquefied halogen (such as aqueous chlorine) accumulation. The second volume 707 can be located below the first volume, thereby taking advantage of the liquefied halogen having a higher density than the remaining electrolyte components. However, depending on the type and operation of separation device 703 and the particular electrolyte and halogen components, volume 707 may be located above or to the side of volume 705.

[0093] An appropriate molecular sieve or membrane can 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.

[0094] 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.

[0095] 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. Patent 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 2 A to 10 A (e.g., zeolite powder or bead sieves, such as Grace Davison SYLOSIV^® brand powders), silica gel with pore widths of 40 A to 100 A, 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 75 A and 2,400 A. 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 andpolyethylene 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 ionexchange (dextran gel ion exchangers), may also be used.

[0096] 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 vessel 101, 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 reservoir 119. 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.

[0097] It should be noted that the first volume 705 does not have to exclusively contain only the remaining electrolyte components and that the second volume 707 does 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 device 703 is sufficient. Thus, the first volume 705 may contain the liquefied halogen in addition to the remaining electrolyte components and the second volume 707 may contain the remaining electrolyte components in addition to the liquefied halogen, as long as there is a higher liquefied halogen concentration in volume 707 than in volume 705, and/or as long as there is a higher remaining electrolyte components concentration in volume 705 than in volume 707. 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 device 703 can 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.

[0098] In the discharge mode of flow battery operation illustrated in FIG. 7, the feed line 607 has an inlet in the second volume 707 of the reservoir 119 below the separation device 703, 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 volume 707 into the flow loop. The inlet 605 of the discharge pump intakes the fluid from the first volume 705, which has a higher concentration of the remaining electrolyte components than volume 707. Optionally, the inlet 605 of the discharge pump may be omitted or may remain inoperative during discharge mode if sufficient electrolyte is present in the second volume 707. 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 reservoir 119. Preferably, the mixture is discharged into the first volume 705 from charge pump inlet/outlet 606. However, a different, separate outlet may be used to discharge the mixture into volume 705 from the flow loop. Unused halogen reactant selectively or preferentially permeates through the separation device 703 (i.e., halogen reactant permeates through device 703 at a higher rate than the remaining electrolyte components) and selectively or preferentially accumulates in the second volume 707. Other electrolyte components have a lower permeability through the separation device 703 than the halogen and preferentially remain in the first volume 705. A concentration difference described above is thus established and maintained with the help of the separation device 703.

[0099] In the charge mode illustrated in FIG. 8, the remaining electrolyte components in the first volume 705 are fed into the flow loop by the charge pump inlet 606 located in the first volume 705 above the separation device 703. The concentrated halogen in the second volume 707 is 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 reservoir 119. Preferably, the fluid is discharged from the discharge pump inlet / outlet 605 into the first volume 705. However, a different, separate outlet may be used to discharge the fluid into volume 705 from the flow loop. The discharged fluid is separated by the separation device 703, the halogen reactant selectively permeates into the second volume 707, leaving a higher concentration of the electrolyte component(s) in the first volume 705 than in the second volume 707.

Third Embodiment of the Separation Device

[00100] Figure 9 illustrates another embodiment of the reservoir 119 which has a separation device 903. The reservoir 119 of the embodiment of Figure 9 may be used with the system and method of any of the embodiments described above. The separation device 903 as shown is configured to separate the heavier and lighter components of the electrolyte employing a combination of mechanisms, such as mechanical separation using a meshed screen or a perforated plate, reducing the flow speed (as the separation device 903 can also act as a baffle), centrifugal force as a result of adopting an axial- symmetric geometry (e.g., a funnel or truncated cone 903 which is substantially symmetric about its axis, such as the vertical axis), and gravity.

[00101] The separation device 903 comprises a curved sheet with openings in its sidewall, such as a meshed or porous screen or a curved perforated plate. Preferably, the sheet has a truncated cone or funnel shape. A truncated cone or funnel shaped separator has a circular or oval horizontal cross sectional shape and an opening on the first end (e.g., the upper end in Figure 9) having a larger size than an opening on the opposite second end (e.g., the lower end). The truncated cone shape shown in Figure 9 may have a steady increase in cross sectional size from the second to the first end and a relatively constantly sloped sidewall (e.g., having a substantially conical shape tapered toward the lower portion of the reservoir 119). A funnel shape (not shown) may have a non-steady increase (i.e., a jump) in cross sectional size from the second to the first end and one or more curves in the sloped sidewall. The separation device 903 divides the reservoir 119 into two volumes 905, 907, with the first volume 905 provided for accumulation of lighter components of the electrolyte, and the second volume 907 provided for accumulation of heavier components, such as aqueous chlorine.

[00102] The discharge flows 909/911 , 913/915 can form a rotating flow of fluid adjacent the upper surface of the separation device 903, as facilitated by outlets 805A, 805B which are bent or curved in a direction substantially along the curved surface of the separation device 903. The outlets 805 A and 805B face into the inner volume of the truncated cone shaped sheet 903 and are curved in the direction of the curvature of the sheet 903 to provide an angular component to the outlet fluid flow, such that the fluid flow spirals around the upper surface of the sheet 903. The resulting centrifugal force together with gravity help heavier components in the fluid to settle into the second volume 907. The apertures 917 in the perforated plate, mesh or screen 903 not only let the heavier components pass into the second volume 907, but also help slow down the flow of the fluid.

[00103] The inlets / outlets 805A and 805B may function similar to the inlets and outlets 605, 606 in Figures 6-8 of the prior embodiments in a system which operates reversibly. As described with respect to the prior embodiments, when the system is operating in the discharge mode, the return (i.e., discharge or outlet) flow 913 will travel from the stack through discharge mode return conduit 822 (similar to conduit 122 in Figure 1) and exits as flow 915 from outlet 805B into the first volume 905 inside the truncated cone shape separation device 903. The chlorine feed (i.e., suction) 921 from the lower, second volume 907 is provided from the feed line 807 through discharge mode feed conduit 815 (similar to conduit 115 in Figure 1) into the stack. Likewise, the electrolyte feed (i.e., suction) from the upper, first volume 905 is provided from the inlet 805 A through conduit 815 into the stack. The chlorine and the electrolyte are mixed in conduit 815 above inlet 805 A. The pump(s) which provide the suction are not shown for clarity. In the non-limiting configuration shown in Figure 9, the discharge mode feed conduit 815 extends vertically down the central axis of the truncated cone sheet 903 and the bottom part of conduit 815 which extends below the bottom opening of truncated cone sheet 903 functions as the chlorine feed line 807. The inlet 805 A into conduit 815 is located between the top and bottom openings of the truncated cone sheet 903. The discharge mode return conduit 822 may extend vertically off the central axis of the sheet 903 and terminate at opening 805B inside the cone above the plate surface 903. When the system is operating in the charge mode, the outlet flow 909 will travel from the stack through conduit 815 (which now functions as the charge mode outlet conduit) and exit as flow 911 from outlet 805 A (which functioned as an inlet in the discharge mode) into the first volume 905 inside the truncated cone shape separation device 903. An intake opening 806 located in charge mode feed conduit 822 above separation device 903 may be used to provide the fluid 919 to the stack in the charge mode, similar to the inlet 606 in Figure 8. Opening 805B may also be used as an inlet in the charge mode. In this embodiment, the separation device 903 uses existing fluid flow dynamics and gravity to facilitate separation of the electrolyte components, and there are no additional moving parts, thereby reducing the additional fixed and operational costs.

Fourth Embodiment of the Separation Device

[00104] Figure 10 illustrates another embodiment of the reservoir 119 which has a separation device 1003. The reservoir 119 of the embodiment in Figure 10 may be used with the system and method of any of the embodiments described above. The separation device 1003 as shown is configured to separate the heavier and lighter components of the electrolyte employing mechanisms similar to those described above with respect to Figure 9, except that the truncated cone or funnel shaped plate 1003 shown in Figure 10 is turned 180 degrees (i.e., upside down) from the orientation of sheet 903 in Figure 9.

[00105] In one embodiment, the separation device 1003 comprises curved sheet, which in some configurations contains openings in its sidewall, such as a meshed or porous screen or a curved perforated plate. Preferably, the sheet has a truncated cone or funnel shape, as described above. In other configurations, the sheet 1003 lacks openings in its sidewall. As shown in Figure 10, device 1003 has a truncated cone shape tapered toward the top portion of the reservoir 119 (i.e., with the opening on the first end (e.g., the upper end in Figure 10) having a smaller size than an opening on the opposite second end (e.g., the lower end). The separation device 1003 divides the reservoir 119 into two volumes 1005, 1007, with the first volume 1005 provided for accumulation of lighter components of the electrolyte, and the second volume 1007 provided for accumulation of heavier components, such as aqueous chlorine. [00106] The discharge flows 911, 915 can form a rotating flow of fluid adjacent the lower surface of the separation device 1003, as facilitated by outlets 805 A and 805B, which are located adjacent to the bottom surface of the sheet 1003 (rather than the upper surface of the sheet 903 in Figure 9). Outlets 805A, 805B are bent or curved in a direction substantially along the curved lower surface of the separation device 1003. The resulting centrifugal force together with gravity helps heavier components in the fluid to better settle into the second volume 1007. Thus, in the embodiment of Figure 10, the separation of the electrolyte and chlorine into volumes 1005 and 1007, respectively, occurs by an upward flow of the electrolyte from volume 1007 into volume 1005. In contrast, in the embodiment of Figure 9, the separation occurs by the downward flow of the chlorine from volume 905 into volume 907.

[00107] 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.

[00108] 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.

Claims

WHAT IS CLAIMED IS:

1. An electrochemical system comprising a vessel, wherein the vessel contains:

(a) at least one cell that comprises:

a first electrode;

a second electrode; and

a reaction zone between the first and second electrodes;

(b) a reservoir containing a first volume configured to selectively accumulate metal-halide electrolyte component and a second volume configured to selectively accumulate a liquefied halogen reactant;

(c) a separation device separating the first volume from the second volume; and

(d) a flow circuit configured to deliver the halogen reactant and the metal- halide electrolyte between the reservoir and the at least one cell.

2. The system of claim 1, wherein the separation device has a higher permeability to the liquefied halogen reactant than the metal-halide electrolyte component.

3. The system of claim 2, wherein the separation device comprises a molecular sieve or a selective porous membrane.

4. The system of claim 3, wherein the molecular sieve or selective porous membrane comprises a molecular sieve selected from at least one of granular natural or synthetic silica-alumina materials or a mesoporous carbon material.

5. The system of claim 3, wherein the separation device comprises a porous container or tray having the molecular sieve therein or thereon.

6. The system of claim 2, wherein the separation device having a higher permeability to the liquefied halogen reactant than the metal-halide electrolyte component is based on at least one of a molecular size or an electrical charge.

7. The system of claim 2, further comprising electrodes or conductive plates electrically contacting the separation device to apply a voltage to the separation device to facilitate selective diffusion of the liquefied halogen reactant through the separation device.

8. The system of claim 1, wherein the separation device comprises a sump plate.

9. The system of claim 1, wherein the separation device comprise a curved sheet with at least two openings.

10. The system of claim 9, wherein:

the curved sheet comprises a truncated cone or funnel shaped curved sheet having a first opening on its upper end and a second opening on its lower end;

the curved sheet is configured to facilitate the separation using a centrifugal force;

the first volume is located above the curved sheet; and

the second volume is located below the curved sheet.

11. The system of claim 10, wherein the curved sheet is tapered toward a lower portion of the reservoir.

12. The system of claim 11, wherein the curved sheet comprises a mesh, screen or perforated plate which contains openings in its sidewall.

13. The system of claim 12, wherein the flow circuit comprises at least one outlet of a return conduit that is curved substantially along an upper surface of the curved sheet.

14. The system of claim 13, wherein:

the flow circuit further comprises at least one feed conduit which extends vertically down a central axis of the curved sheet; and a bottom part of the at least one feed conduit extends through and below the second opening of the curved sheet into the second volume to function as a halogen reactant feed line.

15. The system of claim 10, wherein the curved sheet is tapered toward an upper portion of the reservoir.

16. The system of claim 15, wherein the flow circuit comprises at least one outlet of a return conduit that is curved substantially along a lower surface of the curved sheet.

17. The system of claim 1, wherein the first volume has a higher concentration of the metal-halide electrolyte component than the second volume.

18. The system of claim 17, wherein the second volume has a higher concentration of halogen reactant than the first volume.

19. The system of claim 18, wherein the second volume is located below the first volume in the reservoir.

20. The system of claim 19, wherein the flow circuit is a loop circuit configured to deliver the metal-halide electrolyte component and the halogen reactant from the first and second volumes, respectively, to the at least one cell and from the at least one cell to the reservoir.

21. The system of claim 20, wherein the flow circuit comprises:

a feed manifold configured to deliver the metal-halide electrolyte component and the halogen reactant from the first and second volumes, respectively, to the at least one cell; and

a return manifold configured to deliver the halogen reactant and the metal- halide electrolyte component from the at least one cell to the reservoir.

22. The system of claim 21, wherein the feed manifold comprises:

a first inlet located in the first volume; and

a second inlet located in the second volume.

23. The system of claim 1, wherein a pressure in an inner volume of the vessel is above a liquefication pressure for the halogen reactant.

24. The system of claim 1, wherein the flow circuit comprises:

a first circulation pump configured to convey a flow through the flow circuit in a first direction; and

a second circulation pump configured to convey a flow through the flow circuit in a second direction that is opposite to the first direction.

25. The system of claim 1, wherein the reservoir contains one or more baffle plates configured to reduce eddy currents in the reservoir.

26. The system of claim 1, wherein the reservoir is located below the at least one cell.

27. The system of claim 1, wherein the first electrode comprises a porous material, the second electrode comprises a metal, the metal-halide electrolyte component comprises zinc chloride, the electrolyte comprises an aqueous electrolyte, the liquefied halogen reactant comprises a liquefied chlorine reactant, and the at least one cell comprises a vertical stack of horizontal cells connected in series.

28. A method of operating an electrochemical system, comprising:

(A) providing a system comprising a vessel which contains:

(a) at least one cell that comprises:

a first electrode;

a second electrode; and

a reaction zone between the first and second electrodes; and

(b) a reservoir containing a first volume and a second volume separated by a separation device;

(B) mixing a metal-halide electrolyte component from the first volume and a liquefied halogen reactant from the second volume to form an electrolyte mixture;

(C) providing the electrolyte mixture to the at least one cell in a discharge mode to generate electricity; and (D) returning the electrolyte mixture from the at least one cell to the first volume in the reservoir, such that unused liquefied halogen reactant from the returned electrolyte mixture permeates from the first volume through the separation device to the second volume.

29. The method of claim 28, wherein the first volume has a higher concentration of the metal-halide electrolyte component than the second volume and the second volume has a higher concentration of halogen reactant than the first volume.

30. The method of claim 29, further comprising:

(E) providing the metal-halide electrolyte component from the first volume to the at least one cell in a charge mode to charge the electrochemical system; and

(F) returning the electrolyte from the at least one cell to the first volume in the reservoir, such that the any liquefied halogen reactant in the returned electrolyte selectively from the first volume through the separation device to the second volume.

31. The method of claim 28, wherein the separation device comprises a molecular sieve or a selective porous membrane, the first electrode comprises a porous carbonaceous material, the second electrode comprises zinc, the metal-halide electrolyte component comprises zinc chloride, the electrolyte mixture comprises an aqueous electrolyte mixture, the liquefied halogen reactant comprises a liquefied chlorine reactant, and the at least one cell comprises a vertical stack of horizontal cells connected in series.

32. The method of claim 31, wherein the liquefied halogen reactant selectively permeates from the first volume through the separation device to the second volume based on at least one of having a molecular size smaller than that of the metal-halide electrolyte component or an electrical charge which is different than that of the metal-halide electrolyte component.

33. The method of claim 28, wherein the separation device comprises a sump plate.

34. The method of claim 28, wherein the separation device comprise a curved sheet with at least two openings.

35. The method of claim 34, wherein:

the first volume is located above the curved sheet; and

the second volume is located below the curved sheet.

36. An electrochemical system comprising a vessel, wherein the vessel contains:

(a) at least one cell that comprises:

a first electrode;

a second electrode; and

a reaction zone between the first and second electrodes;

(b) a reservoir containing a first volume configured to selectively accumulate a metal-halide electrolyte component and a second volume configured to selectively accumulate a liquefied halogen reactant; and

(c) flow circuit configured to deliver the halogen reactant and the metal-halide electrolyte between the reservoir and the at least one cell, wherein the flow circuit comprises:

(i) a feed manifold configured to deliver the metal-halide electrolyte component and the halogen reactant from the first and second volumes, respectively, to the at least one cell, the feed manifold comprising a first inlet located in the first volume, and a second inlet located in the second volume; and

(ii) a return manifold configured to deliver the halogen reactant and the metal-halide electrolyte component from the at least one cell to the reservoir.

37. The system of claim 36, wherein the first volume is located above the second volume in the reservoir, the first electrode comprises a porous material, the second electrode comprises a metal, the metal-halide electrolyte component comprises zinc chloride, the electrolyte comprises an aqueous electrolyte, the liquefied halogen reactant comprises a liquefied chlorine reactant, the at least one cell comprises a vertical stack of horizontal cells connected in series, and the stack is located above the reservoir in the vessel.

38. An electrochemical system comprising a sealed vessel that contains:

(a) at least one cell that comprises:

a first metal electrode;

a second porous electrode; and

a reaction zone between the first and second electrodes;

(b) a liquefied chlorine reactant;

(c) at least one metal-chloride electrolyte; and

(d) a closed loop flow circuit configured to deliver the chlorine reactant and the at least one metal-chloride electrolyte to and from the reaction zone, wherein the chlorine reactant and the metal-halide reactant have the same flow path in the closed loop flow circuit in the at least one cell.

39. A metal halogen electrochemical system, comprising:

(A) a pressure containment vessel that contains:

(a) a vertical stack of horizontally positioned cells, wherein each cell of the stack comprises:

at least one positive electrode;

at least one negative electrode; and

a reaction zone between the positive electrode and the negative electrode; and

(b) an electrolyte mixture comprising (i) at least one aqueous electrolyte comprising a metal and a halogen and (ii) a pressurized halogen reactant; and (B) a circulation pump that is configured to convey a flow of the electrolyte mixture through the reaction zone so that the halogen reactant is reduced at the positive electrode to form a halogen ion rich electrolyte mixture, which passes by the negative electrode.

40. An electrochemical system, comprising:

a pressurized sealed vessel that has an inner volume that comprises a first pressure zone and a second pressure zone that surrounds the first pressure zone, wherein:

A) the first pressure zone contains:

(a) at least one cell that comprises:

a first electrode;

a second electrode; and

a reaction zone between the first and second electrodes;

(b) a liquefied halogen reactant;

(c) at least one metal-halide electrolyte; and

(d) a flow circuit configured to deliver the halogen reactant and the at least one electrolyte to the at least one cell; and

B) a pressure in the first pressure zone is above a liquefication pressure for the halogen reactant, while a pressure in the second pressure zone is above the pressure in the first pressure zone.

41. An electrochemical system, comprising:

a pressurized sealed vessel that contains:

(a) at least one cell that comprises:

a first electrode;

a second electrode; and

a reaction zone between the first and second electrodes;

(b) a liquefied halogen reactant;

(c) at least one metal-halide electrolyte; (d) a reservoir containing the at least one metal-halide electrolyte and the liquefied halogen reactant; and

(e) a flow circuit configured to deliver the halogen reactant and the metal- halide electrolyte between the reservoir and the at least one cell;

wherein a pressure in an inner volume of the vessel is above a liquefication pressure for the halogen reactant; and

wherein the reaction zone of the cell does not contain a membrane or a separator that is impermeable to the halogen reactant.

42. The system of claim 41, wherein the system does not comprise a compressor.

43. The system of claim 41, wherein the halogen reactant is located below the at least one metal-halide electrolyte in the reservoir.

44. The system of claim 41, wherein the flow circuit is a loop circuit configured to deliver the halogen reactant and the at least one electrolyte from the reservoir to the at least one cell and from the at least one cell to the reservoir.

45. The system of claim 44, wherein the flow circuit comprises a feed manifold configured to deliver the halogen reactant and the at least one electrolyte from the reservoir to the at least one cell and a return manifold configured to deliver the halogen reactant and the at least one electrolyte from the at least one cell to the reservoir.

46. The system of claim 45, wherein the feed manifold comprises a first intake line and a second intake line, which is separate from the first intake line, wherein the first intake line is configured to intake the metal-halide electrolyte and the second intake line is configured to intake the halogen reactant.

47. The system of claim 46, wherein the halogen reactant is at least partially separated by gravity below the at least one metal-halide electrolyte in the reservoir.

48. The system of claim 47, wherein the second intake line extends below the first intake line in the reservoir.

49. The system of claim 46, wherein the return manifold is an upward flowing return manifold.

50. The system of claim 44, wherein the flow circuit comprises at least one circulation pump configured to convey the halogen reactant and the at least one electrolyte through the reaction zone of the cell.

51. The system of claim 50, wherein the flow circuit comprises a first circulation pump, that is configured to convey a flow through the flow circuit in a first direction and a second circulation pump, that is configured to convey a flow through the flow circuit in a second direction that is opposite to the first direction.

52. The system of claim 50, wherein an inlet of the at least one circulation pump is a horizontal inlet protruding a wall of the reservoir.

53. The system of claim 44, wherein the reservoir contains at least one horizontal sump plate that separates the halogen reactant from the electrolyte in the reservoir.

54. The system of claim 44, wherein the reservoir contains one or more baffle plates configured to reduce eddy currents in the reservoir.

55. The system of claim 43, wherein the reservoir is located below the at least one cell.

56. The system of claim 43, wherein the sealed vessel has a first pressure zone, that contains the reservoir and the at least one cell, and a second pressure zone, enveloping the first pressure zone, wherein a pressure in the second zone is higher than a pressure in the first zone.

57. The system of claim 56, wherein the pressure in the first pressure zone ranges from 75 to 400 psi and the pressure in the second pressure zone ranges from 100 to 600 psi.

58. The system of claim 56, wherein the second pressure zone contains at least one of an inert gas or a neutralizer for the halogen reactant.

59. The system of claim 41, wherein the first electrode comprises a porous carbonaceous material.

60. The system of claim 59, wherein the at least one cell comprises a horizontal cell and wherein an inlet for the halogen reactant and the at least one electrolyte is located above the first electrode and an outlet for the halogen reactant and the at least one electrolyte is located below the first electrode.

61. The system of claim 59, wherein the first electrode further comprises one or more conductive spacers.

62. The system of claim 59, wherein the second electrode comprises zinc, wherein the electrolyte comprises zinc chloride; and wherein the halogen reactant comprises a liquefied chlorine reactant.

63. The system of claim 62, wherein the electrolyte further comprises at least one of sodium chloride and potassium chloride.

64. The system of claim 41, wherein the at least one cell comprises a plurality of cells.

65. The system of claim 64, wherein the at least one cell comprises a plurality of cells connected in series.

66. The system of claim 64, wherein the at least one cell comprises a vertical stack of horizontal cells connected in series.

67. An electrochemical system, comprising a vessel, wherein the vessel contains:

(a) a vertical stack of horizontal cells connected in series;

(b) a reservoir configured to accumulate a metal-halide electrolyte component and a liquefied halogen reactant; and

(c) a flow circuit configured to deliver the halogen reactant and the metal- halide electrolyte between the reservoir and the stack;

wherein:

(i) a first cell in the stack comprises:

a porous electrode;

a metal electrode; and

a reaction zone between the porous and metal electrodes;

(ii) a second cell in the stack comprises:

a porous electrode;

a metal electrode; and

a reaction zone between the porous and metal electrodes;

(iii) electrically conductive spacers electrically contact the porous electrode of the first cell and the metal electrode of the second cell; and (iv) the electrically conductive spacers are configured such that the halogen reactant and the metal-halide electrolyte flow in a space between the electrically conductive spacers, through the porous electrode of the first cell and into the reaction zone of the first cell.

68. The system of claim 67, wherein the reaction zones of the first and the second cells do not contain a membrane or a separator that is impermeable to the liquefied halogen reactant, the metal-halide electrolyte component comprises zinc chloride, the electrolyte comprises an aqueous electrolyte, the liquefied halogen reactant comprises a liquefied chlorine reactant.

69. The system of claim 67, wherein a cell to cell distance between the first cell and the second cell is at least three times greater than an interelectrode distance between the porous electrode of the first cell and the metal electrode of the first cell.