Mitigation of electrolyte mist and gases in electrochemical cells

Abstract

A lid for an electrochemical cell has at least one through-opening connecting a headspace of the cell with an external environment when the lid covers the cell. The at least one through-opening is blocked by at least one hydrophobic, non-electrolyte-absorbing semi-permeable membrane. The semi-permeable membrane is substantially impermeable to electrolyte (e.g., potassium hydroxide) mist while permitting diffusion of hydrogen gas and air therethrough. The semi-permeable membrane has a total permeable surface area in a range of 1-15% of a total surface area of the lid between the headspace of the cell and the external environment. Gases diffuse through the semi-permeable membrane at a rate to maintain a total pressure in the headspace greater than ambient air pressure in the external environment and less than about 0.5 kPa above the ambient air pressure in the external environment. The lid mitigates electrolyte mist venting from and H2 gas accumulation in the cell.

Description

[0001] MITIGATION OF ELECTROLYTE MIST AND GASES IN ELECTROCHEMICAL CELLS

[0002] Cross-reference to Related Applications

[0003] This application claims the benefit of USSN 63 / 730,498 filed December 11 , 2024, the entire contents of which are herein incorporated by reference.

[0004] Field

[0005] This application relates to electrochemical cells, in particular to apparatuses and methods for mitigating electrolyte mist (e.g., potassium hydroxide (KOH) mist) and gases (e.g., hydrogen (H2) and oxygen O2) in electrochemical cells, for example metal-air batteries such as zinc-air batteries.

[0006] Background

[0007] In many electrochemical cells, for example metal-air batteries, hydrogen gas and / or oxygen gas evolves during cell charge, discharge, or during idle due to parasitic discharge of the cell. Further, the evolution of such gases during charge, discharge or idle causes an electrolyte mist (e.g., KOH mist when KOH in water is the electrolyte) to form in the headspace of the cell. It is desirable to be able to remove evolved gases from the headspace of the cell to prevent pressure buildup in the cell, but it is undesirable to permit escape of the electrolyte mist (e.g., KOH + water) from the cell and it is undesirable to allow hydrogen to accumulate in the cell headspace to form explosive mixtures. Without a solution to the above problems, an electrochemical cell would be unsafe and would not pass relevant regulatory certification processes.

[0008] Vents and hydrogen recombinators are the primary methods by which hydrogen and oxygen gas evolution is mitigated. Hydrogen recombinators involve a catalyst material that causes the evolved hydrogen gas to react with the evolved oxygen gas to form water. However, the reaction to recombine hydrogen with oxygen is too slow and the gas evolution rates are too high in some instances for the hydrogen recombinatorto successfully prevent pressure buildup in the headspace. Additionally, hydrogen recombinators protrude from the cell lid, which decreases the overall packing density of cells. In cells where a large amount of hydrogen is produced, recombinators are insufficient to handle the hydrogen effectively without causing the recombinators to heat to temperatures that melt plastic components on which the recombinators are supported. Furthermore, vents are not generally large enough to provide sufficient gas flow through to prevent pressure buildup in the cell. However, simply increasing the size of the vents results in localized influx of unwanted environmental air that can cause failure of battery components and increased loss of water due to evaporation and diffusion through the vent.

[0009] There remains a need for a simple and effective way of preventing buildup of gas pressure in the cell while preventing escape of electrolyte mist and localized influx of unwanted environmental air.

[0010] A lid for an electrochemical cell comprises at least one through-opening connecting a headspace of the electrochemical cell with an external environment when the lid covers the electrochemical cell, the at least one through-opening blocked by at least one hydrophobic, non-electrolyte-absorbing semi-permeable membrane, wherein the at least one semi-permeable membrane is substantially impermeable to an electrolyte mist while permitting diffusion of hydrogen gas and air therethrough, wherein the at least one semi- permeable membrane has a total permeable surface area in a range of 1-15% of a total surface area of the lid between the headspace of the cell and the external environment, wherein gases diffuse through the at least one semi-permeable membrane at a rate to maintain a total pressure in the headspace greater than ambient air pressure in the external environment and less than about 0.5 kPa above the ambient air pressure in the external environment.

[0011] It has now been found that by utilizing one or more hydrophobic, non-electrolyte- absorbing semi-permeable membranes to block one or more carefully sized through- openings in a lid of an electrochemical cell, for example a metal-air electrochemical cell such as a zinc-air battery, it is possible control the total pressure in the headspace of the cell to a pressure that is greater than ambient air pressure in the external environment and less than about 0.5 kPa above the ambient air pressure in the external environment thereby ensuring that hydrogen and other gases in the headspace of the cell can escape at a rate that both prevents pressure buildup in the cell and does not exchange air or moisture too rapidly with the environment, while simultaneously preventing escape of the electrolyte mist from the cell through the through-openings into the external environment. The lid does not require a hydrogen gas management structure that comprises a hydrogen recombinator catalyst to achieve a suitable balance between total pressure in the headspace of the cell and ambient air pressure or to maintain appropriate hydrogen concentrations in the headspace of the cell and in the external environment around the cell. 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.

[0012] Brief of the

[0013] For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which:

[0014] Fig. 1A depicts a top view of a lid for a zinc-air battery showing locations of membrane-covered through-openings.

[0015] Fig. 1 B depicts a side view of Fig. 1 A.

[0016] Fig. 2A is a schematic diagram depicting a lid for a zinc-air battery showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0017] Fig. 2B is a schematic diagram depicting a lid for a zinc-air battery showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0018] Fig. 2C is a schematic diagram depicting a lid for a zinc-air battery showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0019] Fig. 2D is a schematic diagram depicting a lid for a zinc-air battery showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0020] Fig. 2E is a schematic diagram depicting a lid for a zinc-air battery showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0021] Fig. 2F is a schematic diagram depicting a lid for a zinc-air battery showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0022] Fig. 2G is a schematic diagram depicting a lid for a zinc-air battery showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0023] Fig. 3A is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid. Fig. 3B is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0024] Fig. 3C is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0025] Fig. 3D is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0026] Fig. 3E is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0027] Fig. 3F is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0028] Fig. 3G is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0029] Fig. 3H is a schematic diagram depicting an embodiment of a lid for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing another embodiment of a configuration for membrane-covered through-openings in the lid.

[0030] Fig. 4 depicts a graph (left panel) of hydrogen concentration (ppm) in a headspace of an electrochemical cell vs. time (hr) over 10 discharge cycles showing the buildup of hydrogen gas at various locations in the headspace as measured by an array of individual sensors in the lid (right panel).

[0031] Detailed Description

[0032] The electrochemical cell lid described herein provides for dilution of hydrogen gas (H2) in the headspace of the cell by permitting diffusion of the H2 out of the cell through at least one through-opening in the lid while preventing electrolyte mist (e.g., potassium or sodium hydroxide (KOH or NaOH) mist comprising KOH or NaOH, and water) from escaping the cell by virtue of the at least one hydrophobic, non-electrolyte-absorbing semi- permeable membrane blocking (e.g., covering) the at least one through-opening. The semi- permeable membrane is impermeable to water and electrolyte liquid and droplets, while being permeable to hydrogen, oxygen and other atmospheric gases. Important for the dual result is that the at least one semi-permeable membrane has a total permeable surface area in a range of 1-15% of a total surface area of the lid between the headspace of the cell and the external environment. Because the at least one semi-permeable membrane blocks the at least one through-opening, control of the area of the at least one through- opening can be used to control the total permeable surface area of the at least one semi- permeable membrane in the lid. In some embodiments, the total permeable surface area of the at least one semi-permeable membrane within a range of 1-5% of a total surface area of the lid between the headspace of the cell and the external environment. In some embodiments, the range is 2-4%.

[0033] The range of 1-15% for the total permeable surface area of the at least one semi- permeable membrane strikes an optimal balance between the diffusion of hydrogen out of the cell and diffusion of air into the cell so that the concentration of hydrogen in the headspace of the cell is maintained at a level of less than about 10,000 ppm and the total pressure in the headspace of the cell is maintained at an amount greater than the ambient air pressure in the external environment and less than about 0.5 kPa above the ambient air pressure in the external environment. By maintaining the total pressure in the headspace in this pressure range, a continuous diffusion of hydrogen out of the cell is maintained at a high enough rate to prevent buildup of pressure in the cell and to keep hydrogen concentration in the cell below about 10,000 ppm while not imposing stress on the other cell components that can be susceptible to creep, leakage, and flooding. Thus, the various conflicting requirements are kept within the desired ranges. If the total permeable surface area of the at least one semi-permeable membrane is less than 1%, hydrogen and oxygen will not diffuse quickly enough to the external environment to prevent pressure buildup in the cell and hydrogen will not diffuse quickly enough to keep the hydrogen concentration in the cell below about 10,000 ppm. Further, if the total permeable surface area of the at least one semi-permeable membrane is more than 15%, unwanted gaseous species in the environment may come into the headspace of the cell at an unacceptable rate and water loss of the cell through the membrane will be increased. Further, a pressure difference above 0.5 kPa between the cell’s head space and ambient pressure can cause accelerated degradation of cell components, including increased creep of the cell materials as well as additional stress on air cathodes which can cause leakage in the cell. Furthermore, it is desirable to prevent the cell’s external environment from reaching electrolyte (e.g., KOH or NaOH) concentrations of greater than or equal to 2 mg / m3. Thus, in some embodiments, the at least one semi-permeable membrane prevents diffusion of the electrolyte mist therethrough so that an electrolyte concentration in the external environment adjacent the lid remains less than 2 mg / m3, as measured by NIOSH Method 7401), during operation of the electrochemical cell. If the total permeable surface area of the at least one semi-permeable membrane is more than 15%, there is a greater rate of water evaporative loss in the cell.

[0034] While a single through-opening is possible, a plurality of through-openings is preferable, while still limiting the total permeable surface area of the at least one semi- permeable membrane within a range of 1-15% of a total surface area of the lid between the headspace of the cell and the external environment. The plurality of through-openings could be blocked by a single semi-permeable membrane or by a plurality of individual semi- permeable membranes. Blocking the plurality of through-openings with a single semi- permeable membrane would result in some portions of the semi-permeable membrane not being utilized and can be more difficult to implement. For this reason, providing each through-opening with its own semi-permeable membrane is preferred. In some embodiments, the lid is provided with 2-10 through-openings. In some embodiments, the lid is provided with 2-5 through-openings.

[0035] The use of a plurality of membrane-blocked through-openings is beneficial for at least two reasons. First, ingress of carbon dioxide (CO2) gas into the cell can lead to electrolyte poisoning thereby reducing efficiency of the cell. Smaller individual through- openings reduces the amount of CO2ingress. Second, hydrogen distribution in the cell is not necessarily homogeneous throughout the cell causing hydrogen ‘hot spots’ in the headspace depending on the individual cell. Configuring the size, location and spacing of a plurality of membrane-blocked through-openings in the lid leads to more efficient hydrogen mitigation in the cell. Thus, strategic placement of multiple semi-permeable membranes in the lid can help prevent dead zones in the headspace where hydrogen can accumulate.

[0036] The at least one semi-permeable membrane is hydrophobic to prevent passage of liquid water molecules and other dissolved ionic or polar molecules therethrough and non- electrolyte-absorbing to prevent swelling of the membrane. In some embodiments, the at least one semi-permeable membrane has no appreciable weight gain or loss after 1 week of submersion in the electrolyte. A non-absorbing semi-permeable membrane is defined as a membrane that exhibits a weight change of less than 5% wt% after being soaked in the electrolyte for 1 week, in accordance with ASTM D570-98 standard test. As a result, the electrolyte mist (e.g., KOH or NaOH mist) beads on an inner surface of the membrane to eventually fall back into the bulk electrolyte reservoir once a droplet of sufficient mass has formed. Each semi-permeable membrane is thus impermeable to the electrolyte mist while being permeable to hydrogen, oxygen and other atmospheric gases. This has the added advantage of recycling electrolyte into the bulk electrolyte reservoir, thereby maintaining electrolyte levels in cell leading to less requirement for water balancing systems in the cell. Each semi-permeable membrane is also preferably chemically compatible with the electrolyte (e.g., KOH or NaOH) so that the electrolyte does not chemically degrade the membrane.

[0037] In some embodiments, each semi-permeable membrane comprises a fluoropolymer (for example, a polytetrafluoroethylene (PTFE), a polyvinylidene difluoride (PVDF) or a perfluoroalkoxy alkane (PFA)), a polyolefin (for example, polypropylene (PP) or polyethylene (PE)), copolymers of the above, or the like. An example of a suitable semi- permeable membrane is Porous PTFE PMV30 from POREX™. In some embodiments, each semi-permeable membrane comprises a single layer of material, although multilayered structures are possible. However, use of a single layer reduces complexity and cost over the use of multilayer stacks of material.

[0038] In some embodiments, the at least one semi-permeable membrane has a thickness in a range of 50-1000 microns. In some embodiments, the thickness is in a range of 100- 400 microns.

[0039] In some embodiments, the at least one semi-permeable membrane has an air permeability in a range of 0.5 x 10-14m2to 1 1 x 10-14m2. In some embodiments, the air permeability in a range of 1 x 10-14m2to 5 x 10-14m2. Air permeability of the semi-permeable membrane is determined in accordance with the following procedure:

[0040] An 8 cm x 4 cm sample of the membrane is placed between two halves of a sample holder that has two cavities on either side, each having a port that connects the cavity to the environment and one side having an additional port that connects to the environment. The two halves of the sample holder form an airtight seal around the sample. To the sample holder with two ports (inlet chamber) is connected an air cylinder with a pressure gauge and rotameter in line to one port. To the sample holder with one port (outlet chamber), a mass flow meter is connected. Add 6 inches of water of pressure to the one side of the sample. Record the volumetric flow rate and temperature from the mass flow meter on the outlet chamber. Increase the pressure value by 6 inches of water and record the volumetric flow rate and temperature from the mass flow meter on the outlet chamber. Repeat this step to a maximum pressure differential of 30 inches of water. Calculate the permeability using Daryl’s law: where, Qg= outlet air volumetric flow rate (m3.s-1), kp= membrane’s air permeability (m2), Pi= gauge pressure of inlet chamber (Pa), Pa= atmospheric pressure (Pa), A = membrane’s exposed area to air flow (i.e. chamber’s cross-sectional area) 10-3(m2), 5 = thickness of the membrane (m), and = air viscosity (Pa.s); which can be calculated at a specific temperature: p = (0.048 x T + 17.166) x 10-6.

[0041] In some embodiments, the at least one semi-permeable membrane has a mean pore size in a range of 0.1-5 microns. In some embodiments, the mean pore size in a range of 0.5-2 microns.

[0042] In some embodiments, the at least one semi-permeable membrane has a water entry pressure of 100 mBar or greater. In some embodiments, the water entry pressure is 500 mBar or greater. In some embodiments, the water entry pressure is in a range of 100- 1 ,500 mBar. In some embodiments, the water entry pressure is in a range of 500-1 ,000 mBar. The water entry pressure is preferably sufficiently high to ensure that no bulk electrolyte flows through the at least one semi-permeable membrane during transport and handling of the electrochemical cell.

[0043] In some embodiments, the at least one semi-permeable membrane is integrated into the lid such that the at least one semi-permeable membrane does not significantly extend above a top surface of the lid adjacent the at least one semi-permeable membrane, for example, does not extend more than 1.5 cm above the lid adjacent the at least one semi-permeable membrane. Integration of the at least one semi-permeable membrane into the cell lid allows for closer packing of the cells, which results in increased energy density. Having a plurality of through-openings and / or integrating structural features in the lid also helps prevent bursting of the at least one semi-permeable membrane if the cell were to tip over. In some embodiments, the at least one semi-permeable membrane comprises a support structure to provide greater mechanical strength to the membrane, thereby further reducing the chance of the at least one semi-permeable membrane being damaged under pressure. In some embodiments, the support structure reduces tension on seals between the at least one membrane and the lid, which further helps prevent damage to the membranes and electrolyte spill in case of turnovers of the cell. In some embodiments, the at least one semi-permeable membrane is flat across a length and width of the at least one semi-permeable membrane. In some embodiments the at least one semi-permeable membrane is associated with an adjustable feature to provide further control over the the total permeable surface area of the at least one semi-permeable membrane.

[0044] Fig. 1 A and Fig. 1 B depict one embodiment of a lid 1 for a zinc-air battery comprising four through-openings 3 each covered by a semi-permeable membrane 5. The semi- permeable membranes 5 are integrated into the lid 1 and supported in frames 7 to provide extra mechanical strength for the membranes 5. Other features of the lid 1 include a filling port 11 , electrical terminal connections 13, air ports 15 for a discharge section of the battery, electrolyte recirculation inlets 17, bolt holes 19 (only one labeled) around a perimeter of the lid 1 for bolting the lid 1 to a tank of the battery, a mezzanine 21 for housing a cathode wiper system, and a wiper motor 23 for operating the wiper system.

[0045] Fig. 2A to Fig. 2G depict schematic diagrams of the lid 1 showing seven different configurations for the through-openings 3 covered by the semi-permeable membranes 5. Only the through-openings 3 covered by the membranes 5 are depicted. Other features of the lid 1 are omitted for simplicity.

[0046] Fig. 2A depicts four rectangular through-openings 3 covered by semi-permeable membranes 5, the through-openings configured in a longitudinal line along a longitudinal centerline of the lid 1 with the lengths of the through-openings aligned with the longitudinal centerline. Two of the through-openings are located in the mezzanine 21 and the other two through-openings are located proximate opposite ends of the lid 1. All the through-openings have the same size.

[0047] Fig. 2B depicts six rectangular through-openings 3 covered by semi-permeable membranes 5. Two of the through-openings are located proximate opposite ends of the lid 1 , the same as in Fig. 2A, while four of the through-openings are located in the mezzanine 21 and are spaced apart in a rectangular configuration where the center of the rectangle and the center of the lid 1 are the same location on the lid 1. The four through-openings in the mezzanine 21 are smaller than the two rectangular through-openings proximate the ends of the lid 1.

[0048] Fig. 2C depicts four rectangular through-openings 3 covered by semi-permeable membranes 5 as seen in Fig. 2A, except that the two rectangular through-openings proximate the ends of the lid 1 are rotated so that the lengths of the two rectangular through- openings proximate the ends of the lid 1 are perpendicular to the longitudinal centerline of the lid 1.

[0049] Fig. 2D depicts three rectangular through-openings 3 covered by semi-permeable membranes 5, the through-openings configured on a longitudinal line along a longitudinal centerline of the lid 1 with the lengths of the through-openings parallel with the longitudinal centerline. One of the through-openings is located in the mezzanine 21 at a center-point of the lid 1 and the other two through-openings are located proximate opposite ends of the lid 1. The through-opening located in the mezzanine 21 is larger than the other two through- openings.

[0050] Fig. 2E depicts four rectangular through-openings 3 covered by semi-permeable membranes 5. The configuration of the through-openings is similar to Fig. 2D except that there are two smaller through-openings located proximate one end of the lid 1 instead of one large through-opening and that the two smaller through-openings are not located on the longitudinal centerline of the lid 1 but are located closer to the long edges of the lid 1.

[0051] Fig. 2F depicts five rectangular through-openings 3 covered by semi-permeable membranes 5. A central larger through-opening is located in the mezzanine 21 at a center of the lid 1 with a length of the through-opening parallel with the longitudinal centerline of the lid 1. Four smaller through-openings are located proximate opposite ends of the lid 1 but not on the longitudinal centerline, the four smaller through-openings spaced apart in a rectangular configuration where the center of the rectangle and the center of the lid 1 are the same.

[0052] Fig. 2G depicts eight rectangular through-openings 3 covered by semi-permeable membranes 5. Four through-openings are located in the mezzanine 21 and are spaced apart in a rectangular configuration where the center of the rectangle and the center of the lid 1 are the same. The other four through-openings are located at opposite ends of the lid 1 and are spaced apart in a rectangular configuration where the center of the rectangle and the center of the lid 1 are the same. None of the through-openings are located on the longitudinal centerline of the lid 1.

[0053] Fig. 3A to Fig. 3H depict schematic diagrams of a lid 31 for a zinc-air battery without a mezzanine for a charge cathode wiper system but showing eight different configurations for the through-openings 33 covered by semi-permeable membranes 35. Only the through- openings 33 covered by the membranes 35 are depicted. Other features of the lid 31 are omitted for simplicity.

[0054] Fig. 3A depicts the through-openings configured in the same manner as Fig. 2F. Fig. 3B depicts the through-openings configured in the same manner as Fig. 2B. Fig. 3C depicts the through-openings configured in the same manner as Fig. 2A. Fig. 3D depicts the through-openings configured in the same manner as Fig. 2D. Fig. 3E depicts the through-openings configured in the same manner as Fig. 2E. Fig. 3F depicts the through- openings configured in the same manner as Fig. 2C. Fig. 3G depicts the through-openings configured in the same manner as Fig. 2G.

[0055] Fig. 3H depicts two rectangular through-openings 33 covered by semi-permeable membranes 35, the through-openings configured in a longitudinal line along a longitudinal centerline of the lid 31 symmetrically disposed on each side of the center of the lid 31 with the lengths of the through-openings aligned with the longitudinal centerline. The through- openings have the same size.

[0056] Fig. 4 depicts a graph (left panel) of hydrogen concentration (ppm) in a headspace of an electrochemical cell vs. time (hr) as the cell is operated. The graph shows the buildup of hydrogen gas at various locations in the headspace as measured by an array of individual sensors in the lid (right panel). The graph shows that hydrogen gas accumulates more towards the longitudinal ends of the cell over time and that the greatest concentration of hydrogen gas occurs at opposite longitudinal ends of the cell. For this reason, when designing a configuration of semi-permeable membranes for use in this cell for hydrogen mitigation, the lid should be equipped with a plurality of membrane-covered through- openings ensuring that there are through-openings proximate the longitudinal ends. Different cells have different patterns of hydrogen gas accumulation so the most effective configuration of semi-permeable membranes will vary from cell to cell.

[0057] 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 lid for an electrochemical cell, the lid comprising at least one through-opening connecting a headspace of the electrochemical cell with an external environment when the lid covers the electrochemical cell, the at least one through-opening blocked by at least one hydrophobic, non-electrolyte absorbing semi-permeable membrane, wherein the at least one semi-permeable membrane is substantially impermeable to an electrolyte mist while permitting diffusion of hydrogen gas and air therethrough, wherein the at least one semi-permeable membrane has a total permeable surface area in a range of 1-15% of a total surface area of the lid between the headspace of the cell and the external environment, wherein gases diffuse through the at least one semi-permeable membrane at a rate to maintain a total pressure in the headspace greater than ambient air pressure in the external environment and less than about 0.5 kPa above the ambient air pressure in the external environment.

2. The lid of claim 1 , wherein the electrolyte mist comprises potassium or sodium hydroxide electrolyte.

3. The lid of claim 1 or claim 2, wherein the at least one through-opening comprises a plurality of through-openings blocked by the at least one semi-permeable.

4. The lid of claim 3, wherein the plurality of through-openings comprises 2-5 through- openings.

5. The lid of any one of claims 1 to 4, wherein the total permeable surface area of the semi-permeable membrane in contact with headspace is in a range of 1-5% of the total surface area of the lid between the headspace of the cell and the external environment.

6. The lid of any one of claims 1 to 5, wherein the at least one semi-permeable membrane maintains a hydrogen gas concentration in the headspace of the cell of less than about 10,000 ppm.

7. The lid of any one of claims 1 to 6, wherein the at least one semi-permeable membrane prevents diffusion of the electrolyte mist therethrough so that an electrolyte concentration in the external environment adjacent the lid remains less than 2 mg / m3during operation of the electrochemical cell.

8. The lid of any one of claims 1 to 7, wherein the at least one semi-permeable membrane comprises polytetrafluoroethylene.

9. The lid of any one of claims 1 to 8, wherein the at least one semi-permeable membrane has a thickness in a range of 100-400 microns, an air permeability in a range of 1 x 10-14m2to 5 x 10-14m2, a mean pore size in a range of 0.1-5 microns, or any combination thereof.

10. The lid of any one of claims 1 to 9, wherein the lid does not comprise a hydrogen gas management structure that comprises a hydrogen recombinator catalyst.1 1 . The lid of any one of claims 1 to 10, further comprising structural supports for the at least one semi-permeable membrane, the structural supports reducing a chance of the at least one semi-permeable membrane being damaged under pressure.

12. The lid of any one of claims 1 to 1 1 , wherein the at least one semi-permeable membrane is integrated into the lid.

13. The lid of any one of claims 1 to 12, wherein the at least one semi-permeable membrane is flat across a length and width of the at least one semi-permeable membrane.

14. The lid of any one of claims 1 to 13, wherein each semi-permeable membrane comprises a single layer of material.

15. The lid of any one of claims 1 to 14, wherein, the at least one semi-permeable membrane prevents diffusion of the electrolyte mist therethrough so that an electrolyte concentration in the external environment adjacent the lid remains less than 2 mg / m3, as measured by NIOSH Method 7401 ,

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