Electrochemical cell with horizontal air cathode

Abstract

An electrochemical cell includes a cathode subassembly having a housing for a gas volume. The housing has a cathode, a cathode frame for the cathode, and a gas manifold sealed to the cathode frame. The gas manifold has a plurality of gas flow channels defined by a plurality of transversely spaced-apart longitudinally extending rows of baffles protruding therefrom. The baffles both distribute gas flow in the manifold and support the cathode from below. The volume of the incoming gas is larger than the volume of the outgoing gas in the gas manifold. By assembling an upper part of the cell including a tank, an electrolyte recirculation manifold, an anode subassembly and a separator and a lower part of the cell including a cathode subassembly, and then assembling the upper and lower parts together, the gap between the anode and cathode can be optimized for better regularity and efficiency.

Description

[0001] ELECTROCHEMICAL CELL WITH HORIZONTAL AIR CATHODE

[0002] Cross-reference to Related

[0003] This application claims the benefit of USSN 63 / 736,409 filed December 19, 2024, the entire contents of which is herein incorporated by reference.

[0004] Field

[0005] This application relates to electrochemical cells.

[0006] Typical charge / discharge type electrochemical cells comprise a tank containing a reservoir of liquid electrolyte in which electrodes (cathodes and anodes) are situated, the tank housing a discharging section generally located at or near a bottom of the tank and a charging section generally located at or near a top of the tank, with a storage section for liquid electrolyte located in between the charging and discharging sections. The charging section operates to store electrical energy in the electrochemical cell and the discharging section operates to deliver the stored electrical energy to operate an electrical device. The charging and discharging sections are generally not operated at the same time.

[0007] Charge / discharge type electrochemical cells can utilize Zn / Zn2+half-cell reactions in a basic aqueous electrolyte. The charging section comprises charge anodes and charge cathodes at which the following chemical reactions occur during a charging operation:

[0008] Charge anode: 4OH- - O2+ 2H2O + 4e_

[0009] Charge cathode: Zn(OH)42-+ 2e - Zn(s)+ 4OH-

[0010] The discharging section comprises discharge anodes and discharge cathodes at which the following chemical reactions occur during a discharging operation:

[0011] Discharge anode: Zn(s)+ 4OH- —» Zn(OH)42-+ 2e

[0012] Discharge cathode: O2+ 2H2O + 4e_- 4OH-

[0013] Elemental zinc solid formed at the charge cathode falls to the bottom of the electrochemical cell under the influence of gravity to collect on a metal current collector, which carries current to operate electrical devices when the solid zinc is converted back to Zn(OH)42-during the discharging operation of the electrochemical cell. The discharge cathodes are typically vertically oriented in the tank. A bed of zinc solid builds up around the discharge cathodes during the charging operation and is depleted from around the discharge cathodes during the discharging operation. There are a number of problems with this arrangement. Zinc bed depletion from around the discharge cathodes increases the distance between the discharge cathode and the zinc and therefore reduces cell efficiency and shortens the life of the discharge cathode especially when the discharge cathode is an air cathode. The vertically oriented discharge cathodes act as baffles to prevent side-to-side movement of the solid zinc and the electrolyte in the cell during the discharging operation causing differential depletion of the zinc bed. The differential depletion of the zinc bed is also exacerbated by varying discharge cathode performance in the vertical discharge cathode orientation which inherently depletes zinc within the zinc bed at different rates. An additional consequence of the above is the formation of differential concentrations of zinc salt in different regions of the electrolyte in the cell thereby causing voltage differentials at each discharge cathode, worsening the differential depletion of zinc problem. In another problem associated with vertical discharge cathodes, during the charging operation, solid zinc is inhibited from falling down to the bottom of the cell by the discharge cathodes with some solid zinc accumulating on upper edges of the vertically oriented discharge cathodes, which are not electrochemically active portions of the discharge cathodes. All these problems lead to inefficient zinc usage and unreacted solid zinc during the discharging operation.

[0014] WO 2023 / 245276 published December 28, 2023, the entire contents of which is herein incorporated by reference, describes an electrochemical cell having a horizontally oriented discharge cathode. While the electrochemical cell described therein has significant advantages over previously developed air cathode cells, there still remains a need for an electrochemical cell design, and a discharging section therefor, which provides for simpler liquid electrolyte recirculation, better distribution of air across the cathode and greater efficiency and regularity of half-cell reactions across the interface between the cathode and anode.

[0015] An electrochemical cell comprises: a tank configured to contain a liquid electrolyte; an anode subassembly situated in the tank in a discharging section of the tank, the anode subassembly comprising: an anode comprising a solid anode material in physical contact with the liquid electrolyte when the liquid electrolyte is in the tank; a horizontally oriented cathode subassembly situated in the tank in the discharging section of the tank and below the anode subassembly, the cathode subassembly comprising: a cathode comprising a gaseous oxygen (O2) cathode material housed in a gas volume, the cathode subassembly configured to separate the gas volume from the liquid electrolyte above the gas volume, the gaseous oxygen cathode material capable of diffusing out of the gas volume into an interface region where the gaseous oxygen contacts the liquid electrolyte; and, a housing for the gas volume, the housing defined by a cathode in which oxygen gas is diffusible, a cathode frame bounding and sealing edges of the cathode, and a gas manifold sealed to the cathode frame below the cathode; and, a separator comprising an electrically insulating material, the separator separating the cathode from the anode, the separator permeable to the liquid electrolyte, the separator impermeable to the solid anode material.

[0016] A cathode subassembly for an electrochemical cell comprises a housing for a gas volume for a gaseous oxygen (O2) cathode material, the housing comprising: a cathode in which oxygen gas is diffusible; a cathode frame bounding and sealing edges of the cathode; and, a gas manifold sealed to the cathode frame below the cathode to form the gas volume defined by the cathode at a top of the housing, the gas manifold at a bottom of the housing and the cathode frame at sides of the housing.

[0017] A gas manifold for a cathode subassembly comprises a plate comprising a face, a first end, and a second end longitudinally spaced-apart from the first end, the face comprising a plurality of gas flow channels therein defined by a plurality of transversely spaced-apart longitudinally extending rows of gas-flow-distributing baffles protruding from the face, each baffle spaced-apart longitudinally from neighboring baffles in a given row, the first end of the plate comprising a gas inlet whereby incoming gas enters the gas inlet and flows longitudinally in the gas manifold before flowing transversely toward a first side of the plate, the first end comprising a gas outlet whereby outgoing gas from a second side of the plate, transversely opposed to the first side of the plate, flows longitudinally out of the gas manifold at the gas outlet at the first end of the plate, wherein a volume of the incoming gas flowing in the gas manifold is largerthan a volume of the outgoing gas flowing in the gas manifold.

[0018] A method of assembling a discharging section of an electrochemical cell comprises: assembling a liquid electrolyte tank together with an electrolyte recirculation manifold, an anode subassembly and a separator to form an upper cell subassembly; assembling a cathode subassembly comprising a housing for a gas volume, the housing defined by a cathode in which oxygen gas is diffusible, a cathode frame bounding and sealing edges of the cathode, and a gas manifold sealed to the cathode frame below the cathode together with a bleeder mesh to form a lower cell subassembly; and, assembling the upper cell subassembly together with the lower cell subassembly thereby forming a gap separating the cathode from the separator with the bleeder mesh in the gap, such that an average separation between the cathode and the separator is in a range of 0.7-1.1 mm and the separation varies no more than 10% from the average across an entire area of the gap.

[0019] Especially in metal-air electrochemical cells, the cathode has a relatively large surface area, providing a challenge to ensuring uniform gas distribution across the entire surface of the cathode. Traditional airboxes are often large to accommodate this need, but their size complicates airflow balancing and results in uneven gas supply across the cathode, creating performance-degrading dead zones. In contrast, the gas manifold described herein is more compact and efficient than previous gas manifolds, achieving uniform air flow distribution across the cell’s large cathode surface while minimizing the airbox’s size. By maintaining a smaller, optimized volume, the gas manifold described herein efficiently supplies gas to all parts of the cathode, which boosts the cell’s performance and prevents dead zones. Additionally, the compact design enhances the cell’s volumetric energy density, enabling greater energy storage in the same physical space.

[0020] Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art.

[0021] Brief Description of the Drawings

[0022] For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which:

[0023] Fig. 1 depicts a perspective view of an assembled electrochemical cell.

[0024] Fig. 2A depicts a perspective view of a cathode and a cathode frame therefor for use in a cathode subassembly for the electrochemical cell of Fig. 1.

[0025] Fig. 2B depicts an exploded view of Fig. 2A.

[0026] Fig. 2C depicts a top perspective view of an end of the cathode frame shown in Fig. 2A.

[0027] Fig. 2D depicts an end cross-sectional view at a corner of the cathode frame shown in Fig. 2A. Fig. 2E depicts a magnified view of an exploded portion of the cathode frame shown in Fig. 2A.

[0028] Fig. 3A depicts an exploded view of a cathode subassembly including the cathode frame and cathode of Fig. 2A and a gas manifold.

[0029] Fig. 3B depicts a top view of the gas manifold shown in Fig. 3A.

[0030] Fig. 3C depicts a cross-sectional view at a corner of the cathode subassembly of Fig. 3A.

[0031] Fig. 3D depicts a cross-sectional perspective view near an end of the cathode subassembly shown in Fig. 3A when assembled.

[0032] Fig. 3E depicts a cross-sectional end view near an end of the cathode subassembly shown in Fig. 3A when assembled.

[0033] Fig. 3F depicts a cross-sectional end view of a corner near an end of the cathode subassembly shown in Fig. 3A when assembled.

[0034] Fig. 4A depicts an exploded view of the cathode subassembly of Fig. 3A together with an electrolyte recirculation manifold and including an electrically insulating separator and an electrolyte bleeder mesh, the electrolyte bleeder mesh located between the electrically insulating separator and the cathode.

[0035] Fig. 4B depicts a perspective view of the cathode subassembly assembled with the electrolyte recirculation manifold, electrically insulating separator and electrolyte bleeder mesh.

[0036] Fig. 4C depicts a magnified cross-sectional end perspective view of the cathode subassembly assembled with the electrolyte recirculation manifold shown in Fig. 4B.

[0037] Fig. 4D depicts a magnified cross-sectional perspective view of a corner of the cathode subassembly assembled with the electrolyte recirculation manifold shown in Fig. 4B where the cross-section is taken closer to the end than the cross-section in Fig. 4C.

[0038] Fig. 4E depicts a top view of an end of the electrolyte recirculation manifold where plumbing for the electrolyte recirculation manifold is located.

[0039] Fig. 5A depicts a cross-sectional perspective view of a lower corner of an electrochemical cell comprising the assembled cathode subassembly of Fig. 3A. Fig. 5B depicts an end view of Fig. 5A.

[0040] Fig. 5C depicts a magnified view of a portion of Fig. 5A.

[0041] Fig. 6 depicts a perspective view of an anode subassembly for the electrochemical cell of Fig. 1.

[0042] Fig. 7A depicts a perspective view of an inner tank for the electrochemical cell of Fig. 1.

[0043] Fig. 7B depicts a perspective view of the inner tank of Fig. 7A assembled with the electrolyte recirculation manifold and the anode subassembly.

[0044] Fig. 7C depicts a top perspective view of the inner tank of Fig. 7A assembled with the electrolyte recirculation manifold, including the plumbing for the electrolyte recirculation manifold and the anode subassembly, to form an upper part of a discharging section of the electrochemical cell.

[0045] Fig. 7D depicts a perspective view of the upper part shown in Fig. 7C being mounted to a lower part of the discharging section of the electrochemical cell, which comprises the cathode frame of Fig. 2A and Fig. 3A.

[0046] Fig. 7E depicts a perspective view of discharging section assembly in which the upper part shown in Fig. 7C is assembled with the lower part, the lower part comprising the cathode subassembly.

[0047] Fig. 7F depicts placement of busbars and cables in the assembly shown in Fig. 7E.

[0048] Fig. 7G depicts how the electrolyte exits an outer tank by way of a triple sealed combiner fitting.

[0049] Detailed Description

[0050] An electrochemical cell (e.g., a metal-air battery such as a zinc-air battery) is provided having a discharge cathode that is substantially horizontally oriented so that a bed of solid anode material settles above the discharge cathode, not beside the discharge cathodes, during a charging operation to cover the entire discharge cathode. During a discharging operation, the bed of anode material is depleted but substantially the entire surface of the discharge cathode remains covered with the bed of anode material throughout the discharging operation because the anode material is depleted from the bottom and depleted anode material is continuously replaced by more anode material in the bed by the action of gravity. Thus, gravity keeps the bed of anode material evenly distributed over an anode current collector and over the discharge cathode.

[0051] As used herein, an anode material is a chemical species that is oxidized (i.e., loses electrons) in a half-cell reaction. The anode material in the discharging section of the electrochemical cell preferably comprises a metal, for example metallic zinc, copper, lead, iron or the like. The anode material is more preferably zinc metal. The anode material is preferably particulate, forming a bed of anode material particles above the separator. The bed of anode material particles is porous to permit flow of liquid electrolyte through the bed to the separator.

[0052] As used herein, an anode is a physical structure that comprises the anode material and is where an anodic half-cell reaction involving the anode material occurs. In the discharging section of the electrochemical cell, the anode comprises the bed of the anode material. The bed of the anode material preferably covers the separator.

[0053] As used herein, an anode current collector is a physical structure that comprises a conductive material used to transport electrons from the anode material. The electrochemical cell preferably comprises an anode current collector situated below and in physical contact with the anode material. The anode current collector is preferably a porous conductive metal mesh. The metal preferably comprises nickel or copper.

[0054] As used herein, a cathode material is a chemical species that is reduced (i.e., gains electrons) in a half-cell reaction. The cathode material in the discharging section of the electrochemical cell preferably comprises an oxidizing gas, preferably gaseous oxygen. The gaseous oxygen is preferably provided as air, more preferably as air which has been scrubbed of carbon dioxide.

[0055] As used herein, a cathode is a physical structure where a cathodic half-cell reaction involving the cathode material occurs. Where the cathode material is an oxidizing gas (e.g., gaseous oxygen), the cathode material resides in the cathode immediately before reacting and is continuously replenished in the cathode as the cathode material reacts.

[0056] As used herein, a cathode current collector is a physical structure that comprises a conductive material used to transport electrons to the cathode material. The cathode current collector is preferably a porous metal mesh. The metal preferably comprises nickel or copper. As used herein, a cathode is preferably an air cathode comprising the cathode current collector and an active layer containing an electrochemically active catalyst for the cathodic half-cell reaction. The catalyst is preferably disposed within the active layer together with conductive carbon and a binder, preferably a hydrophobic binder (e.g., polytetrafluoroethylene (PTFE)). Preferably, the active layer is laminated to the cathode current collector. In some embodiments, the cathode also comprises a backing layer of a hydrophobic material (e.g., PTFE or a mixture of PTFE and conductive carbon), which is permeable to oxygen but impermeable to water to prevent electrolyte from diffusing through the cathode into the air manifold. The cathode comprises an interface region in which the catalyst is situated. In the interface region, the liquid electrolyte and the gaseous oxygen contact each other and the cathodic half-cell reaction occurs. Thus, the liquid electrolyte, the catalyst and the gaseous oxygen form a triple phase boundary at the interface region where the gaseous oxygen reacts to form hydroxide ions.

[0057] As used herein, a separator is a physical structure that comprises a porous electrically insulating material. The separator electrically separates the cathode from the anode material. The separator preferably covers the cathode to prevent anode material from directly contacting the cathode. The separator is permeable to the liquid electrolyte but impermeable to the solid anode material. In this regard, the separator also acts as a filter. The separator preferably has a porosity that creates a pressure differential between above and below the separator to encourage more uniform permeation of the liquid electrolyte through the separator toward the cathode across an entire surface area of the separator. The separator preferably comprises a mat of polypropylene fibers. The mat preferably has a density in a range of 20-100 g / m3, for example 60 g / m3. The mat preferably has a thickness in a range of 80 to 300 microns, for example 180 microns. The mat preferably has an air permeability of 100 to 500 dm3 / second*m2.

[0058] As used herein, the liquid electrolyte is a liquid medium containing anions capable of reacting with oxidized anode material to form an anionic metal complex. Preferably, the liquid medium is an aqueous medium. Preferably, the anions are hydroxide ions, which may be present in solution in the aqueous medium, for example by dissolving an alkali metal hydroxide (e.g., NaOH, KOH) in water to form an aqueous solution of hydroxide ions. The hydroxide ions react with metal cations to form metalate complexes when the anode material is oxidized. In a Zn / Zn2+electrochemical cell, the metalate is Zn(OH)42-having Na+or K+counterions in the electrolyte solution.

[0059] The cathode subassembly is configured to house the gaseous oxygen cathode material in a housing that forms a gas volume. The cathode subassembly therefore acts as a storage unit for the gaseous oxygen cathode material. The cathode is mounted in a cathode frame of the cathode subassembly, the cathode frame bounding and sealing edges of the cathode. The cathode separates the gas volume from the liquid electrolyte above the gas volume. Gaseous oxygen diffuses out of the gas volume into the interface region of the cathode where the gaseous oxygen contacts the liquid electrolyte. The cathode subassembly also comprises a gas manifold sealed to the cathode frame below the cathode to form the gas volume housed by the cathode at a top of the housing, the gas manifold at a bottom of the housing and the cathode frame at sides of the housing.

[0060] In some embodiments of the cathode subassembly, the cathode is horizontally oriented, which is to say at an angle of 45° or less with respect to horizontal, when the cathode subassembly is in use in an electrochemical cell. Preferably, the angle is 10° or less, or 5° or less. In some embodiments, the angle is about 0°, in which case the cathode is flat and horizontally oriented. A flat, horizontally oriented cathode is easier to seal in the cathode frame.

[0061] In some embodiments, the gas manifold comprises a plate comprising a face, a first end, and a second end longitudinally spaced-apart from the first end. In some embodiments, the face comprises a plurality of gas flow channels therein defined by a plurality of transversely spaced-apart longitudinally extending rows of gas-flow-distributing baffles protruding from the face. In some embodiments, each baffle is spaced-apart longitudinally from neighboring baffles in a given row. In some embodiments, at least 90% of the baffles in a common row are longitudinally offset from the baffles in a transversely neighboring row, thereby providing an array of baffles having a staggered look when viewed transversely through the gas manifold. In some embodiments, baffles of larger size and / or different orientation are strategically placed among the plurality of baffles to further optimize gas flow distribution across the cathode. In some embodiments, the first end of the plate of the gas manifold comprises a gas inlet whereby incoming gas enters the gas inlet and flows longitudinally in the gas manifold before flowing transversely (i.e., across a short direction of the gas manifold) toward a first side of the plate. In some embodiments, the first end of the gas manifold comprises a gas outlet whereby outgoing gas from a second side of the plate, transversely opposed to the first side of the plate, flows longitudinally out of the gas manifold at the gas outlet at the first end of the plate. In some embodiments, a volume of the incoming gas flowing in the gas manifold is larger than a volume of the outgoing gas flowing in the gas manifold (i.e., the volumes of incoming gas and outgoing gas in the gas manifold are asymmetrical). In some embodiments, a ratio of the volume of the incoming gas flowing in the gas manifold to the volume of the outgoing gas flowing in the gas manifold is in a range of 2:1 to 4:1 , for example 3:1 . Thus, the gas manifold has a greater total gas volume in the gas flow channels before the gas passes across an underside surface of the cathode than the gas manifold has in the gas flow channels after the gas passes across the underside surface of the cathode. This asymmetry in the before and after total gas volumes in the gas flow channels of the gas manifold defines the asymmetrical volumes of incoming gas and outgoing gas. The gas manifold can be quite large (e.g., about 100 cm in length), which creates gas distribution problems across the entire underside surface of the cathode, which could lead to irregular distribution of electrochemistry over the entire area of the cathode thereby leading to inefficiencies in the electrochemical cell. Each of the features of the gas manifold described above contributes to providing uniform gas flow distribution across the underside surface of the cathode.

[0062] In some embodiments of the cathode subassembly, the cathode frame comprises one or more transversely oriented bridges extending between sides of the cathode frame. The one or more bridges support the cathode from below the cathode. In some embodiments, at least a portion of the baffles of the gas manifold support the one or more bridges from below the one or more bridges. In some embodiments, the one or more bridges comprise a plurality of bridges. Thus, the baffles of the gas manifold serve both to help properly distribute air flow across a lower surface of the cathode and to structurally support the cathode. In some embodiments, the cathode frame comprises a first series of apertures therein situated along the first side of the plate of the gas manifold in fluid communication with the incoming gas in the gas manifold. The first series of apertures direct the incoming gas across the underside surface of the cathode toward the second side of the plate of the gas manifold. In some embodiments, the cathode frame comprises a second series of apertures therein situated along the second side of the plate of the gas manifold in fluid communication with the gas manifold to direct the gas that crossed the underside surface of the cathode into the gas manifold as the outgoing gas. In some embodiments, the apertures in the first series and / or second series of apertures become progressively larger from the first end toward the second end of the plate of the gas manifold.

[0063] In some embodiments, the electrochemical cell comprises an electrolyte recirculation manifold that recirculates the liquid electrolyte from between the anode and cathode back into a liquid electrolyte reservoir stored in the tank above the anode. For this purpose, the electrolyte recirculation manifold comprises internal and external components. In some embodiments, the electrolyte recirculation manifold comprises a recirculation frame that is fitted and sealable to the top of the cathode frame. In some embodiments, the electrolyte recirculation manifold comprises at least one internal fluid conduit, preferably a plurality of internal fluid conduits, contained in the recirculation frame configured to collect liquid electrolyte from between the cathode and the anode. The at least one internal fluid conduit preferably directs the collected liquid electrolyte to at least one recirculation outlet through which the liquid electrolyte exits the electrolyte recirculation manifold back into the tank above the anode.

[0064] In some embodiments, the electrolyte recirculation manifold comprises a balancing cartridge insert that comprises a plurality of recirculation inlets situated between the cathode and the separator for collecting the liquid electrolyte from along edges of the cathode outside the gas volume and directing the collected liquid electrolyte to the at least one internal fluid conduit inside the electrolyte recirculation manifold, which directs the liquid electrolyte to the at least one recirculation outlet through which the liquid electrolyte is returned to the liquid electrolyte reservoir above the anode. In some embodiments, the electrolyte recirculation manifold houses the separator. In some embodiments, the electrolyte recirculation manifold is configured to recirculate the liquid electrolyte that permeates through the separator back to the liquid electrolyte above the separator through a liquid electrolyte recirculation path that is entirely above the cathode subassembly. In some embodiments, the liquid electrolyte in the recirculation path does not pass through the separator. Thus, the liquid electrolyte passes through the separator only once before being recirculated back to the storage section of the tank, which is beneficial for maintaining better control over pressure in the electrolyte recirculation manifold.

[0065] In some embodiments, the recirculation manifold comprises at least one external fluid conduit in fluid communication with the at least one internal fluid conduit. In some embodiments, the at least one external fluid conduit is connected to at least one fluid pump operative for pumping the collected liquid electrolyte through and out of the at least one external fluid conduit through the at least one recirculation outlet into the electrochemical cell at the top of the liquid electrolyte reservoir above the separator.

[0066] In some embodiments, a method of assembling a discharging section of an electrochemical cell comprises assembling an upper cell assembly and a lower cell assembly, and then assembling the upper with the lower cell to form the discharging section of the electrochemical cell. The upper cell assembly is formed by assembling the liquid electrolyte tank together with the electrolyte recirculation manifold, the anode subassembly and the separator. In some embodiments, the separator is sealed to the electrolyte recirculation manifold, preferably to cover the bottom of the electrolyte recirculation manifold. In some embodiments, the anode subassembly is housed within the recirculation frame above the separator. The lower cell assembly is formed by assembling the cathode subassembly, and then assembling the cathode subassembly together with a bleeder mesh, the bleeder mesh being placed on top of the cathode. The upper cell assembly is then assembled with the lower cell assembly thereby forming a gap separating the cathode from the anode with the bleeder mesh in the gap between the cathode and the separator. This “two-part” final assembly method provides greater control over the height and regularity of the gap between the cathode and the anode permitting optimization of the gap height for more efficient electrochemical connection between the cathode and anode. In some embodiments, the gap provides an average separation between the cathode and the anode is in a range of 0.7- 1.1 mm and the separation varies no more than 10% from the average across an entire area of the gap.

[0067] In some embodiments, the electrochemical cell comprises an outer case within which the assembled upper and lower cell assemblies is secured. In some embodiments, the case is provided with insulation to provide greater structural integrity and protection against heat, shock, and / or leakage.

[0068] The following describes an embodiment of an electrochemical cell with reference to the Figures.

[0069] Fig. 1 depicts an electrochemical cell 1 having an upper charging section 2, a middle storage section 3 and a lower discharging section 4. The cell 1 comprises an inner tank 5 in which a reservoir of liquid electrolyte is contained, the same liquid electrolyte being used in both the charging and discharging operations of the cell 1. The electrochemical cell 1 comprises a lid 6 to which many of the elements of the charging operation are connected. The discharging section 4 comprises an electrolyte recirculation manifold 10 and an air cathode subassembly 50.

[0070] Fig. 2A to Fig. 3F depict the cathode subassembly 50 comprising an air cathode 51 having edges bounded and sealed into a cathode frame 53, the cathode frame 53 comprising an upper frame 53a and a lower frame 53b between which edge portions of the cathode 51 are captured. The cathode subassembly 50 also comprises an air manifold 60 sealingly attached to a lower face of the lower frame 53b to form a gas volume defined at a top by the cathode 51 , at a bottom by the air manifold 60 and at the sides by the cathode frame 53.

[0071] The cathode 51 comprises an active layer laminated to a cathode current collector (e.g., copper mesh). The cathode 51 also comprises a hydrophobic backing layer, which is permeable to oxygen but impermeable to water to prevent electrolyte from diffusing through the cathode 51 into the air manifold 60. The cathode 51 is flat and is horizontally oriented when the cathode subassembly 50 is assembled into the cell 1. The cathode 51 extends out through an outside edge of the cathode frame 53 and is connected to bus bars 54, which are mounted on the lower face of the lower frame 53b when the cathode subassembly 50 is assembled. The bus bars 54 extend longitudinally under the lower frame 53b along a lower face of the lower frame 53b. The bus bars 54 terminate in cathode terminals 54a for electrically connecting the cathode 51 to other electrical components. The bus bars 54 are external elements of the cathode subassembly 50 and are not exposed to the electrolyte so are not potted in a sealing adhesive such as epoxy resin.

[0072] The upper frame 53a and the lower frame 53b are laminated together to capture edge portions of the cathode 51 therebetween as best seen in Fig. 2B, Fig. 2D, Fig. 3C and Fig. 3F. The upper frame 53a and the lower frame 53b each comprise a locating feature 52 for properly nesting the cathode 51 between the upper and lower frames 53a, 53b, respectively, when assembling the cathode subassembly 50. The locating feature 52 comprises protrusions in a lower face of the upper frame 53a and an upper face of the lower frame 53b, which are mated with corresponding apertures in the bus bars 54. The upper frame 53a comprises a perimetrical groove 56a in the lower face thereof and the lower frame 53b has a corresponding perimetrical groove 56b in the upper face thereof such that when the upper frame 53a and the lower frame 53b are laminated together, the grooves 56a, 56b form a perimetrical interior channel 57 in the cathode frame 53 across which the cathode 51 extends. The channel 57 is filled with an adhesive sealant (e.g., epoxy resin) to seal the cathode frame 53 around the edges of the cathode 51 to prevent gas from entering or leaving the gas volume through the cathode frame 53 and to help bond the upper and lower frames 53a, 53b together. The upper frame 53a further comprises a perimetrical groove 58 (see Fig. 3C) on an upper face thereof to assist with properly indexing and mounting the electrolyte recirculation manifold 10 on the cathode frame 53 when assembling the discharging section 4 of the cell 1. The upper frame 53a comprises two transverse bridges 59 for joining three cathode sections that make up the cathode 51 in the cathode frame 53. With specific reference to Fig. 2C, the cathode frame 53 further comprises a plurality of transversely oriented ribs 55 (only one labeled) that support the cathode 51 from below the cathode 51. The ribs 55 are connected to and extend between the longitudinal sides of the lower frame 53b as best seen in Fig. 2C. The ribs 55 are uninterrupted and chamfered and have a depth that ensures that the gaseous cathode material passes even if the weight of the electrolyte slightly deflects the cathode 51. With specific reference to Fig. 3A to Fig. 3F, the air manifold 60 is bonded, preferably permanently, to the lower face of the lower frame 53b at a contact interface 62 therebetween using an adhesive (e.g., ABS cement). The contact interface 62 comprises a locating feature 61 designed to properly nest the frame 53 with the air manifold 60. The locating feature 61 comprises complementarily mated steps between the lower face of the lower frame 53b and an upper face of the air manifold 60 at the contact interface 62 therebetween. The air manifold 60 comprises a plate 63 having a first end 64 and a second end 66 longitudinally spaced-apart from the first end 64. The plate 63 has a longer longitudinal direction L-L and a shorter transverse direction T-T. The plate 63 comprises an array of air-flow-distributing baffles 65 protruding from an upper face of the plate 63, the array of baffles 65 (only four labeled in Fig. 3B) defining a plurality of air flow channels 67 (only three labeled Fig. 3B) in the air manifold 60 to contribute to providing uniform distribution of air across an underside surface of the cathode 51. The baffles 65 form transversely spaced-apart longitudinally extending rows protruding from the upper face of the plate 63, each baffle 65 spaced-apart longitudinally from neighboring baffles 65 in a given row. Most of the baffles 65 in a common row are longitudinally offset from the baffles 65 in a transversely neighboring row. Most of the baffles 65 are short baffles 65a that help define a plurality of transverse and longitudinal air flow channels in the air manifold 60. Some of the baffles 65 are of larger size and / or different orientation than others of the baffles 65 and are strategically placed among the plurality of baffles 65 to further optimize air flow distribution in the air manifold 60. For example, baffle 65b is longer than baffles 65a and is oriented so that a length of the baffle 65b is oriented transversely. For further example, baffle 65c is very long creating a long longitudinal air flow channel 67c without many openings into transversely oriented air flow channels. Some of the baffles 65 have different shapes, for example a cross-shaped baffle 65d. Strategic placement, size and shape of the baffles 65 all contribute to providing uniform airflow rate and distribution. While the baffles 65 of the air manifold 60 serve to help properly distribute air flow across the underside surface of the cathode 51 , at least a portion of the baffles 65 are also strategically placed under the ribs 55 of the cathode frame 53 to structurally support the cathode 51 from below the cathode 51.

[0073] The first end 64 of the plate 63 comprises an air inlet 68, as best seen in Fig. 3E, whereby incoming air enters the air inlet 68 and flows longitudinally in the air manifold 60 through an incoming air volume of the air manifold 60 before flowing transversely toward a first side 71 of the plate 63. The first end 64 of the plate 63 also comprises an air outlet 69, as best seen in Fig. 3E, whereby outgoing air in an outgoing air volume from a second side 72 of the plate 63, transversely opposed to the first side 71 of the plate 63, flows longitudinally out of the air manifold 60. With specific reference to Fig. 3C, Fig. 3E and Fig. 3F, air flowing into the air manifold 60 through the inlet 68 first flows longitudinally in a longitudinal air flow channel about halfway along a length of the air manifold 60 before being distributed into transversely oriented air flow channels to flow toward the first side 71 of the plate 63. At the first side 71 of the plate 63 the air flowing in the incoming air volume is directed upward through a first series of apertures 79 in a longitudinal edge of the cathode frame 53 so that the flowing air is directed transversely along the underside surface of the cathode 51 toward the second side 72 of the plate 63 where the air flowing in the outgoing air volume is directed downward through a corresponding series of apertures in an opposite longitudinal edge of the cathode frame 53 to flow in the outgoing air volume of the air manifold 60. The apertures 79 in the first and second series of apertures become progressively larger from the first end 64 toward the second end 66 of the plate 63 of the air manifold 60 to compensate for pressure loss as the air flows through the air manifold 60 to keep the flow rate uniform across all portions of the cathode 51. Further contribution to uniform air distribution in the air manifold 60 is realized by providing asymmetrical volumes of incoming air and outgoing air. The volume of the incoming air flowing in the air manifold 60 is three times as large as the volume of the outgoing air flowing in the air manifold 60.

[0074] The air manifold 60 thus comprises a designed air flow path and structure that optimizes the flow of air in an air space 75 (see Fig. 3F) across the underside surface of the cathode 51. The air space across the underside surface of the cathode 51 is a few mm thick (e.g., 3 mm thick) and is defined at the perimeter by the lower frame 53b. The air manifold 60 provides unform air velocity (flow rate) and distribution while minimizing the height required to achieve the uniform air velocity and distribution. The baffles 65 both help support the weight of the electrolyte while not impeding air flow as well as deflecting and steering the air in a way that evens out air velocity in the air manifold 60. Combined with the asymmetrical incoming vs. outgoing air volumes and the tuned sizes of the apertures 79, a variation in flow rate (velocity) of 5% or less can be achieved.

[0075] With reference to Fig. 4Ato Fig. 5C, the discharging section 4 of the electrochemical cell 1 also comprises an electrolyte recirculation manifold 10. The recirculation manifold 10 recycles electrolyte that has collected above the cathode 51 back to the electrolyte reservoir in the storage section 3 of the electrochemical cell 1. The recirculation manifold 10 comprises a recirculation manifold frame 11 and a pair of electrolyte intake manifolds 12 located inside and at bottoms of electrolyte intakes 14 in hollow longitudinal sides of the recirculation manifold frame 11. The electrolyte intake manifolds 12 are divided into three zones along lengths thereof corresponding to three sections of the cathode 51. The electrolyte intakes 14 have a locating feature 20 in the form of a step to locate the depth to which the electrolyte intake manifolds 12 are inserted in the electrolyte intakes 14. Divider sections 21 (see Fig. 4D) in the electrolyte intakes 14 act as a load transferring feature from the unsupported lip of the outside wall of the recirculation manifold frame 11. The recirculation manifold frame 11 is nested on the upper frame 53a of the cathode frame 53 in a tongue-and-groove arrangement involving a downwardly oriented perimetrical tongue 13 around the bottom edge of the recirculation manifold frame 11 , the tongue 13 mated with the perimetrical groove 58 on the upper face of the upper frame 53a of the cathode frame 53. The seam between the tongue 13 and the groove 58 is welded so that the recirculation manifold 10 is rigidly connected to the cathode subassembly 50. When assembling the recirculation manifold 10 with the cathode subassembly 50, a separator 80 is first bonded to the recirculation manifold frame 11 and a bleeder mesh 90 is placed on the cathode 51 before the recirculation manifold 10 and the cathode subassembly 50 are assembled together.

[0076] With the recirculation manifold 10 and the cathode subassembly 50 assembled in electrochemical cell 1 , liquid electrolyte permeating through the separator 80 collects above the cathode 51. The electrolyte above the cathode 51 can flow horizontally into the electrolyte intake manifolds 12 at the bottoms of the electrolyte intakes 14 in the recirculation manifold frame 11. The electrolyte intakes 14 in the recirculation manifold frame 11 contain chambers 18 above the electrolyte intake manifolds 12 at the bottoms of the electrolyte intakes 14. The recirculation manifold 10 further comprises recirculation plumbing 15 mounted externally at an end of the recirculation manifold frame 11, the recirculation plumbing 15 comprising fluid conduits 17 connected to both longitudinal sides of the recirculation manifold frame 11 , the fluid conduits 17 combining at a combiner 16 to merge fluid flow exiting the cell 1. The combiner 16 is connected to a fluid pump (not shown) whose operation draws electrolyte evenly from the electrolyte intakes 14 in both longitudinal sides of the recirculation manifold frame 11. The fluid conduits 17 are connected to the chambers 18. Negative pressure applied in the chambers 18 by operation of the fluid pump draws the electrolyte collected from above the cathode 51 evenly into the electrolyte intake manifolds 12 along the entire lengths of the electrolyte intakes 14. The electrolyte is pumped through the chambers 18, through the fluid conduits 17 and through the combiner 16 to be ultimately returned to the tank 5 in the storage section 3.

[0077] The electrolyte recirculation manifold 10 provides a liquid electrolyte recirculation path that is entirely above the cathode subassembly 50. Therefore, the liquid electrolyte being recirculated from between the cathode 51 and the separator 80 needs to permeate through the separator 80 only once, which improves electrolyte flow efficiency by reducing pressure drops.

[0078] Fig. 6 depicts an anode subassembly 40 for the discharging section 4 of the electrochemical cell 1. The anode subassembly 40 comprises an anode current collector 41 , which is formed of an expanded mesh of indium-coated copper and on which the solid anode material (not shown) is supported. The anode current collector 41 is additionally punched to have 2 mm through apertures to allow hydrogen gas to escape if hydrogen is formed. The anode current collector 41 is connected to main anode bus bars 43 and the anode current collector 41 is further equipped with bridge anode bus bars 45 (only one labeled) to help with current collection in a central area of the anode. The main anode bus bars 43 remain in the electrolyte and are not potted in in a sealing adhesive such as epoxy resin.

[0079] Fig. 7A to Fig. 7G depict a method of assembling the discharging section 4 of the electrochemical cell 1. In Fig. 7A, the tank 5 is assembled by bonding the walls and top flange together in a sealed manner, for example by welding and cementing (e.g., with dichloromethane (DCM) adhesive and / or plastic welding). In preparation for assembling the electrolyte recirculation manifold 10 with the tank 5, the separator 80 is bonded to the electrolyte recirculation manifold 10 at a bottom thereof. The anode subassembly 40 is mounted in the electrolyte recirculation manifold 10 above the separator 80 so that the anode subassembly 40 is part of the electrolyte recirculation manifold 10, as shown in Fig. 5C. The tank 5 is assembled into the electrolyte recirculation frame 11 , which now includes the anode subassembly 40, until the tank 5 lands on a ledge 11a (see Fig. 4C and Fig. 4D) of the electrolyte recirculation frame 11. The electrolyte recirculation manifold 10 is assembled to sides of the walls of the tank 5 by welding around the perimeter where the tank 5 meets the electrolyte recirculation manifold 10 As shown in Fig. 7C, the other components of the electrolyte recirculation manifold 10 are then added, including the recirculation plumbing 15, which is also mounted on an end of the tank 5, to form an upper cell assembly 105.

[0080] With reference to Fig. 7D and Fig. 7E, a lower cell assembly 110, formed by adding the bleeder mesh 90 on to the cathode subassembly 50, is assembled with the upper cell assembly 105 by mating the tongue 13 of the recirculation manifold frame 11 with the groove 58 of the upper frame 53a of the cathode subassembly 50, and then welding around the perimeter of the tongue-in-groove connection to form the electrochemical cell 1. As shown in Fig. 7E, a liquid level sensor 106 is mounted in the tank 5, the liquid level sensor 106 triggering when liquid electrolyte level is below a minimum level, which provides information about whether there is a significant leak in the tank 5. As seen in Fig. 7F and Fig. 7G, the electrochemical cell 1 is then outfitted with additional internal bus bars 107, cables 108, and air hoses 109, the cell 1 is lowered into an outer case 115. An external fitting 19 is screwed and glued onto the combiner 16, the external fitting 19 having a fluid port for connection to the fluid pump.

[0081] The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.

Claims

Claims:1 . A gas manifold for a cathode subassembly, the gas manifold comprising a plate comprising a face, a first end, and a second end longitudinally spaced-apart from the first end, the face comprising a plurality of gas flow channels therein defined by a plurality of transversely spaced-apart longitudinally extending rows of gas-flow-distributing baffles protruding from the face, each baffle spaced-apart longitudinally from neighboring baffles in a given row, the first end of the plate comprising a gas inlet whereby incoming gas enters the gas inlet and flows longitudinally in the gas manifold before flowing transversely toward a first side of the plate, the first end comprising a gas outlet whereby outgoing gas from a second side of the plate, transversely opposed to the first side of the plate, flows longitudinally out of the gas manifold at the gas outlet at the first end of the plate, wherein a volume of the incoming gas flowing in the gas manifold is larger than a volume of the outgoing gas flowing in the gas manifold.

2. The gas manifold of claim 1 , wherein a ratio of the volume of the incoming gas flowing in the gas manifold to the volume of the outgoing gas flowing in the gas manifold is in a range of 2: 1 to 4: 1 , preferably 3:1.

3. The gas manifold of claim 1 or claim 2, wherein at least 90% of the baffles in a common row are longitudinally offset from the baffles in a transversely neighboring row.

4. A cathode subassembly for an electrochemical cell, the cathode subassembly comprising a housing for a gas volume for a gaseous oxygen (O2) cathode material, the housing comprising: a cathode in which oxygen gas is diffusible; a cathode frame bounding and sealing edges of the cathode; and, a gas manifold sealed to the cathode frame below the cathode to form the gas volume defined by the cathode at a top of the housing, the gas manifold at a bottom of the housing and the cathode frame at sides of the housing,wherein the gas manifold comprises the gas manifold as defined in any one of claims 1 to 3.

5. The cathode subassembly of claim 4, wherein the cathode frame comprises one or more transversely oriented bridges extending between sides of the cathode frame, the bridges supporting the cathode from below the cathode, and wherein at least a portion of the baffles support the one or more bridges from below the one or more bridges.

6. The cathode subassembly of claim 4 or claim 5, wherein the cathode is flat and horizontally oriented when mounted in the electrochemical cell.

7. The cathode subassembly of any one of claims 4 to 6, wherein the cathode frame comprises: a first series of apertures therein situated along the first side of the plate of the gas manifold in fluid communication with the incoming gas in the gas manifold, the first series of apertures directing the incoming gas across an underside surface of the cathode toward the second side of the plate; and, a second series of apertures therein situated along the second side of the plate of the gas manifold in fluid communication with the gas manifold to direct the gas that crossed the underside surface of the cathode into the gas manifold as the outgoing gas.

8. The cathode subassembly of claim 7, wherein the apertures in the first series and / or second series of apertures become progressively larger from the first end toward the second end of the plate of the gas manifold.

9. An electrochemical cell comprising: a tank configured to contain a liquid electrolyte; an anode subassembly situated in the tank in a discharging section of the tank, the anode subassembly comprising: an anode comprising a solid anode material in physical contact with the liquid electrolyte when the liquid electrolyte is in the tank; a horizontally oriented cathode subassembly situated in the tank in the discharging section of the tank and below the anode subassembly, the cathode subassembly comprising:a cathode comprising a gaseous oxygen (O2) cathode material housed in a gas volume, the cathode subassembly configured to separate the gas volume from the liquid electrolyte above the gas volume, the gaseous oxygen cathode material capable of diffusing out of the gas volume into an interface region where the gaseous oxygen contacts the liquid electrolyte; and, a housing for the gas volume, the housing defined by a cathode in which oxygen gas is diffusible, a cathode frame bounding and sealing edges of the cathode, and a gas manifold sealed to the cathode frame below the cathode; and, a separator comprising an electrically insulating material, the separator separating the cathode from the anode, the separator permeable to the liquid electrolyte, the separator impermeable to the solid anode material.

10. The electrochemical cell of claim 9, further comprising an electrolyte recirculation manifold housing the separator, the electrolyte recirculation configured to recirculate the liquid electrolyte that permeates through the separator back to the liquid electrolyte above the separator through a liquid electrolyte recirculation path that is entirely above the cathode subassembly.11 . The electrochemical cell of claim 9 or claim 10, wherein the liquid electrolyte passes through the separator only once before being recirculated back to the storage section of the tank.

12. The electrochemical cell of any one of claims 9 to 11 , wherein the cathode subassembly is as defined in any one of claims 4 to 8.

13. The electrochemical cell of any one of claims 9 to 12, wherein the solid anode material comprises zinc metal and the gaseous oxygen (O2) cathode material comprises air.

14. A method of assembling a discharging section of an electrochemical cell, the method comprising: assembling a liquid electrolyte tank together with an electrolyte recirculation manifold, an anode subassembly and a separator to form an upper cell assembly;assembling a cathode subassembly comprising a housing for a gas volume, the housing defined by a cathode in which oxygen gas is diffusible, a cathode frame bounding and sealing edges of the cathode, and a gas manifold sealed to the cathode frame below the cathode together with a bleeder mesh to form a lower cell assembly; and, assembling the upper cell assembly together with the lower cell assembly thereby forming a gap separating the cathode from the anode with the bleeder mesh in the gap below the separator, such that an average separation between the cathode and the anode is in a range of 0.7-1.1 mm and the separation varies no more than 10% from the average across an entire area of the gap.

15. A discharging section of an electrochemical cell assembled by the method of claim

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