Composite air electrode and associated manufacturing method

Abstract

A method for manufacturing a composite electrode for a metal-air electrochemical cell with a liquid electrolyte of basic pH. A liquid solution comprising a fluoropolymer suspended in a solvent is synthesized, then deposited on the outer surface of a porous structure forming an air electrode. The fluoropolymer comprises SO 2 N groups suitable for conducting hydroxyl ions and is capable of forming a membrane impermeable to at least the liquid electrolyte of basic pH. When the liquid solution is applied to the porous structure, the solvent flows through the porous structure and the fluoropolymer is deposited by aggregating into a layer on the outer surface of the porous structure.

1 : A method for manufacturing a composite electrode configured to be used in a metal-air electrochemical cell with a liquid electrolyte of basic pH, the method comprising:
 obtaining an air electrode porous structure comprising an outer surface, the porous structure being configured to facilitate an oxygen reduction reaction into hydroxyl ions in the presence of an electric current;   synthesizing a first liquid solution comprising a fluoropolymer suspended in a solvent, the fluoropolymer being capable of forming a membrane impermeable to at least the liquid electrolyte of basic pH, the fluoropolymer comprising SO 2 N groups capable of conducting hydroxyl ions;   applying the first liquid solution at least once onto the outer surface of the porous structure, the solvent flowing through the porous structure and the fluoropolymer being deposited by aggregating into a layer on the outer surface of the porous structure, thereby forming said membrane impermeable to at least the liquid electrolyte of basic pH and conductive to hydroxyl ions.   
     
     
         2 : The method according to  claim 1 , further comprising:
 applying the first liquid solution a second time onto the outer surface of the porous structure,   evaporating the solvent of the first liquid solution applied a second time onto the outer surface of the porous structure.   
     
     
         3 : The method according to  claim 1 , further comprising, during the obtaining of the porous structure:
 incorporating the fluoropolymer comprising SO 2 N groups capable of conducting hydroxyl ions and capable of forming a membrane impermeable to at least the liquid electrolyte of basic pH, into a carbon powder used to prepare the porous structure,   obtaining the porous structure from the carbon powder mixed with the fluoropolymer.   
     
     
         4 : The method according to  claim 1 , wherein the electrode is configured as a positive electrode of a metal-air battery, the pH of the liquid electrolyte being about 14 or higher. 
     
     
         5 : A composite electrode configured to be used in a metal-air electrochemical cell with a liquid electrolyte of basic pH, the composite electrode comprising:
 an air electrode porous structure comprising an outer surface, the porous structure being configured to facilitate an oxygen reduction reaction into hydroxyl ions in the presence of an electric current;   an impermeable membrane of fluoropolymer, the fluoropolymer comprising SO 2 N groups capable of conducting hydroxyl ions, the membrane being impermeable to the liquid electrolyte of basic pH, the membrane being arranged on the outer surface of the porous structure in the form of a layer, the fluoropolymer having a polymerized structure adapted to prevent penetration of said fluoropolymer into the porous structure.   
     
     
         6 : The composite electrode according to  claim 5 , wherein the SO 2 N group is part of a SO 2 NRQ +  group where:
 Q +  is a group comprising at least one quaternary nitrogen atom, 
 R is selected from the group consisting of: hydrogen, an alkyl of the C 1 -C 20  group, a cyclic compound comprising the Q+ group and between 2 and 20 carbon atoms, a cyclic compound comprising the Q+ group, between 2 and 20 carbon atoms, and up to 4 heteroatoms. 
 
     
     
         7 : The composite electrode according to  claim 5 , wherein the fluoropolymer comprises a fluorinated backbone chain with polar groups that are at least partially hydrogenated. 
     
     
         8 : The composite electrode according to  claim 7 , wherein the fluoropolymer further comprises at least one quaternary ammonium group with no hydrogen in a beta-position of the at least one quaternary ammonium group. 
     
     
         9 : The composite electrode according to  claim 5 , wherein the fluoropolymer comprises groups belonging to the family of tetrafluoroethylene and sulfur groups. 
     
     
         10 : The composite electrode according to  claim 5 , wherein a thickness of the protective membrane is between 10 μm and 100 μm. 
     
     
         11 : The composite electrode according to  claim 5 , wherein the porous structure comprises a polymer-based material optimizing the conduction of hydroxyl ions. 
     
     
         12 : The composite electrode according to  claim 11 , wherein the polymer-based material of the porous structure forms an interpenetrating polymer network or a semi-interpenetrating polymer network. 
     
     
         13 : A metal-air battery comprising the composite electrode according to  claim 5 . 
     
     
         14 : The metal-air battery according to  claim 13 , further comprising a metal negative electrode of zinc and a liquid electrolyte of a basic pH of about 14 or higher.