Patent Publication Number: US-2022216549-A1

Title: Pouched metal-air battery cells

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 17/520,304, filed Nov. 5, 2021, which claims the benefit of provisional application No. 63/110,629, filed Nov. 6, 2020, the entire contents of each are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to metal-air batteries and electrodes therein. 
     BACKGROUND 
     Electrochemical devices, such as batteries and fuel cells, typically incorporate an electrolyte source to provide the anions or cations necessary to produce an electrochemical reaction. Batteries and fuel cells operate on the electrochemical reaction of hydrogen-air, metal-air, metal-halide, metal-hydride, metal-intercalation compounds, or other materials capable of electrochemical reaction. 
     Metal-air batteries (or metal-oxygen batteries) with aqueous and non-aqueous electrolytes have attracted industry interest for many years as these reactors can have high energy densities and be relatively inexpensive to produce. Sizes can range from the small to power hearing aids or cameras to the large to power vehicles. 
     A unique property of metal-oxygen batteries compared to other batteries is that the cathode active material (i.e., oxygen) is typically not stored in the battery. When the battery is exposed to the environment, oxygen enters the cell through an oxygen diffusion membrane and porous air electrode and is reduced at the surface of a catalytic air electrode, forming peroxide ions and/or oxide ions in non-aqueous electrolytes or hydroxide anions in aqueous electrolytes. As an example, a mass of metal can form a porous anode that is saturated with an electrolyte. During discharge, oxygen reacts at a cathode to form hydroxyl ions that migrate into the metal-electrolyte to form a metal hydroxide, releasing electrons to travel to a cathode. The metal hydroxide decays into metal oxide and the resulting water returns to the electrolyte. The water and hydroxyls from the anode are recycled at the cathode, so the water is not consumed. The reverse process can also occur. During charge, electrons react with the metal oxide to reform the metal, releasing hydroxyl ions that migrate to the cathode. The hydroxyl ions are then oxidized to oxygen gas and water. 
     SUMMARY 
     A metal air battery cell has an electrode assembly including an air electrode, a negative electrode, a separator in contact with and disposed between the electrodes, and a sealed pouch that envelops the electrode assembly and contains an electrolyte therein. The pouch is defined by a gas permeable hydrophobic flexible layer in contact with the air electrode, and a gas and liquid impermeable flexible layer in contact with the negative electrode. The metal air battery cell further has a metallocene film in contact with and completely covering the gas permeable hydrophobic flexible layer such that the gas permeable hydrophobic flexible layer is between the metallocene film and air electrode. 
     A metal air battery cell has an electrode assembly including an air electrode and a gas permeable hydrophobic flexible layer in contact with the air electrode, a negative electrode, a separator in contact with and disposed between the electrodes, and a sealed pouch that envelops the electrode assembly and contains an electrolyte therein. The pouch is defined by a metallocene film that is in contact with the electrodes and completely covers the gas permeable hydrophobic flexible layer such that the gas permeable hydrophobic flexible layer is between the metallocene film and air electrode. 
     A metal air battery cell has an electrode assembly including two air electrodes and two gas permeable hydrophobic flexible layers, a negative electrode disposed between the air electrodes, at least one separator in contact with and disposed between the air electrodes and negative electrode, and a sealed pouch that envelops the electrode assembly and contains an electrolyte therein. The pouch is defined by a metallocene film in contact with the air electrodes such that the metallocene film is in contact with and completely covers the two gas permeable hydrophobic flexible layers, and each of the gas permeable hydrophobic flexible layers is between the metallocene film and one of the air electrodes. 
     A metal air battery cell has a sealed pouch defined by a metallocene film and a gas and liquid impermeable flexible layer, and an electrochemical cell contained within the pouch. The metallocene film and gas and liquid impermeable flexible layer are sealed to each other and around the electrochemical cell. 
     A metal air battery cell includes an electrochemical cell and a sealed pouch containing the electrochemical cell. The pouch is defined by a metallocene film that envelops the electrochemical cell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are side views, in cross-section, of metal-air pouch cells. 
         FIG. 3  is a plot of discharge voltage versus time for a metal-air pouch cell with a gas reduction layer. 
         FIG. 4  is a plot of discharge voltage versus time for a metal-air pouch cell without a gas reduction layer. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale. Some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     Containment of a metal-air battery usually requires complex ridged structures with pressure seals or adhesives to contain moisture, while also allowing the passage of air to the positive electrode. Here, metal-air pouch cells are described that can contain moisture and also allow the access of needed air by, for example, sealing a gas permeable and hydrophobic material to a gas and liquid impermeable material and/or a gas reduction material. The gas permeable and hydrophobic material may allow gas flow to the air electrode or electrodes while deterring the escape of moisture due to its hydrophobic nature. The gas reduction material may limit the gas flow. These materials can be heat sealed, at ends of the pouch, to a gas and liquid impermeable material. Such a pouch may be simple, light weight, thin, easily manufactured, and cost effective, while providing all of the necessary containment functions for a metal-air cell. 
     Referring to  FIG. 1 , a metal-air battery cell  10  (e.g., an electrochemically rechargeable battery cell, a primary battery cell, etc.) includes an electrode assembly  12  and a pouch  14 . The electrode assembly  12  includes an air electrode (e.g., a bi-directional air electrode)  16 , a negative electrode (e.g., zinc electrode)  18 , and a separator (or membrane)  20  in contact with and between the air electrode  16  and negative electrode  18 . 
     The pouch  14  includes a gas permeable hydrophobic flexible layer  22  in contact with the side of the air electrode  16  opposite the separator  20 , and a gas and liquid impermeable flexible layer  24  in contact with the negative electrode  18  such that the gas permeable hydrophobic flexible layer  22  is not in contact with the negative electrode  18 , and the gas and liquid impermeable flexible layer  24  is not in contact with the air electrode  16 . The gas permeable hydrophobic flexible layer  22  can be non-sintered polytetrafluoroethylene. It can also be polymeric and chemically inert in the electrolyte environment. The pouch  14  further includes a gas reduction layer  26  in contact with the side of the gas permeable hydrophobic flexible layer  22  opposite the air electrode  16 . In other examples, the gas reduction layer  26  is not part of the pouch  14 , but instead heat sealed or otherwise bonded to it. The gas reduction layer  26  can be metallocene, have a thickness in the approximate range of 1 to 30 microns, and/or may have a Gurley air permeability of 10,000 to 50,000 seconds or more. Without the gas reduction layer  26 , the pouch  14  may have a Gurley air permeability in the range of 100 to 500 Gurley seconds. 
     The gas permeable hydrophobic flexible layer  22  (or gas reduction layer  26 ) and the gas and liquid impermeable flexible layer  24  are sealed (e.g., heat sealed) to each other around a perimeter of the pouch  14 . A thermoplastic hot melt or other adhesive can further define a seam for the pouch  14 . As a result, the pouch  14  envelops the electrode assembly  12  and contains an electrolyte  28  within which the electrode assembly  12  is immersed, in contact with, or wetted. The electrolyte  28  may be acidic, alkaline, or neutral. And, it may be a gel, an ionic liquid, a liquid, or a solid. 
     Referring to  FIG. 2 , a metal-air battery cell  110  includes an electrode assembly  112  and a pouch  114 . The electrode assembly  112  includes an air electrode  116 , a negative electrode  118 , and a separator  120  in contact with and between the air electrode  116  and negative electrode  118 . 
     The pouch  114  includes a gas permeable hydrophobic flexible layer  122  in contact with the side of the air electrode  116  opposite the separator  120 , and a gas reduction layer  125  in contact with the negative electrode  118  such that the gas permeable hydrophobic flexible layer  122  is not in contact with the negative electrode  118 , and the gas reduction layer  125  is not in contact with the air electrode  116 . The pouch  114  further includes a gas reduction layer  126  in contact with the side of the gas permeable hydrophobic flexible layer  122  opposite the air electrode  116 . The gas reduction layers  125 ,  126  may be distinct components or portions of one continuous component. 
     The gas permeable hydrophobic flexible layer  122  (or the gas reduction layer  126 ) and the gas reduction layer  125  are sealed to each other around a perimeter of the pouch  114 . A thermoplastic hot melt or other adhesive can further define a seam for the pouch  114 . As a result, the pouch  114  envelops the electrode assembly  112  and contains an electrolyte  128  within which the electrode assembly  112  is immersed, in contact with, or wetted. 
     Other contemplated pouch configurations include a gas reduction layer or layers in contact with and enveloping two gas permeable hydrophobic flexible layers, which are in contact with sides of two air electrodes opposite the separators. The separators are also in contact with one negative electrode. The gas reduction layer or layers may be distinct components or portions of one continuous component. 
     Referring to  FIGS. 3 and 4 , the performance of metal-air pouch cells, of the types contemplated herein, with and without gas reduction layers is noticeably different when tested with a pulse discharge followed by standby current.  FIG. 3  shows that the discharge voltage of a metal-air pouch cell with a gas reduction layer remains relatively consistent well past 2,000 hours of operation.  FIG. 4  shows that the discharge voltage of a metal-air pouch cell without a gas reduction layer significantly degrades after a mere 70 hours. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.