Bilayer electrolyte membrane and a redox flow battery comprising a bilayer electrolyte membrane

Patent metadata

Field	Value
Publication number	US-2021075030-A1
Application number	US-201816962392-A
Country	US
Kind code	A1
Filing date	Dec 5, 2018
Priority date	Jan 15, 2018
Publication date	Mar 11, 2021
Grant date	—

Abstract

An electrolyte membrane and method for generating the membrane provide a resistance as low as possible to minimize ohmic losses. The membrane has a low permeability for redox-active species. If redox-active species still cross the membrane, this transport is balanced during charge and discharge preventing a net vanadium flux and associated capacity fading. The membrane is mechanically robust, chemically stable in electrolyte solution, and low cost. A family of ion exchange membranes including a bilayer architecture achieves these requirements. The bilayer membrane includes two polymers, i) a polymer including N-heterocycles with electron lone pairs acting as proton acceptor sites and ii) a mechanically robust polymer acting as a support, which can be a dense cation exchange membrane or porous support layer. This bilayer architecture permits a very thin polymer film on a supporting polymer to minimize ohmic resistance and tune electrolyte transport properties of the membrane.

First claim

1 - 21 . (canceled)

22 . A bilayer ion exchange membrane for use in electrochemical cells, redox flow batteries and vanadium redox flow batteries, the membrane comprising:
a) an ion exchange polymer layer including N-heterocycles with electron lone pairs acting as proton acceptor sites; b) a mechanically robust polymer substrate as a support layer; and c) a solution-coated or spray-coated attachment of said ion exchange polymer layer with said proton acceptor sites to said support layer.

23 . The membrane according to claim 22 , wherein said polymer layer with said acceptor sites is formed of a polymer including at least 50 mol % of at least one of an imidazole or benzimidazole or benzobisimidazole unit.

24 . The membrane according to claim 22 , wherein said polymer layer with said proton acceptor sites is formed of a polymer including at least one of pyridine or imidazole units in a main chain or as pendant groups with a content of less than 50 mol %.

25 . The membrane according to claim 23 , wherein said polymer layer including said proton acceptor sites is a polybenzimidazole-class polymer including one or more of the following compounds: poly(2,2′-m-phenylene-5,5′-bibenzimidazole) (meta-PBI), poly(2,2′-p-phenylene-5,5′-bibenzimidazole) (para-PBI), poly(2,5′-benzimidazole) (AB-PBI), poly(p-phenylene benzobisimidazole) (PBDI), poly-2,2-(X,Y-pyridine)-5,5′-bibenzimidazole (P—PBI) where (X,Y) is (2,5), (3,5), (2,6) or (2,4), and poly-[(1-(4,4′-diphenylether)-5-oxybenzimidazole)-benzimidazole] (PBI—OO).

26 . The membrane according to claim 25 , wherein said polybenzimidazole-class polymer is functionalized at a nitrogen-hydrogen (NH) site of at least one of said imidazole or benzimidazole or benzobisimidazole.

27 . The membrane according to claim 26 , wherein said functionalization includes a deprotonation of NH of at least one of said imidazole or benzimidazole or benzobisimidazole unit with an alkali hydride followed by an alkylation with an R—X compound, wherein X is a halogen, bromine, or a cyclic compound being opened upon reaction or 1,3-propane sultone.

28 . The membrane according to claim 27 , wherein said R—X compound used for said functionalization yields one or more of the following:
a) crosslinking (including Br—(CH2)n-Br) or Br—(CF2)n-Br);
b) cation exchange functionalities (including Br—(CH2)n-SO3-, Br—(CF2)n-SO3-);
c) Protected acid groups (including Br—CF2-P(═O)(OEt)2, which after an alkylation reaction are hydrolyzed to obtain free phosphonic acid —CF2-P(═O)(—OH)2) or their alkali salts;
d) anion exchange functionalities (including Br—(CH2)n-N+(CH3)3).

29 . The membrane according to claim 25 , wherein said polybenzimidazole-class layer has a thickness which is below 15 μm and is adjustable during preparation.

30 . The membrane according to claim 22 , wherein said support layer is a microporous polyolefin (or polypropylene (e.g. Treopore® PDA), polyethylene (or Celgard® 2500 or Solupor® 3P07A) or a combination thereof.

31 . The membrane according to claim 22 , wherein said support layer is a dense cation exchange membrane containing sulfonate exchange sites (—SO3-).

32 . The membrane according to claim 31 , wherein said cation exchange membrane is a perfluoroalkylsulfonic acid (PFSA) type membrane, or Nafion®, or Fumion®, or Aquivion®, or Flemion®.

33 . The membrane according to claim 31 , wherein said cation exchange membrane is a partially fluorinated or non-fluorinated sulfonic acid type membrane, or a polyarylene type membrane (including polysulfones, polyether ketones, polyphenylenes) or a radiation grafted membrane including styrene type sulfonic acid groups.

34 . The membrane according to claim 22 , which further comprises a proton accepting layer formed of a polybenzimidazole class polymer with a thickness of less than 15 μm, said support layer being formed of a cation exchange membrane with a thickness between 15 and 150 μm.

35 . The membrane according to claim 34 , wherein said support layer is a microporous polyolefine being modified at a surface of a film to at least one of improve wettability of a material or increase adhesion with said proton accepting layer.

36 . The membrane according to claim 35 , wherein said modification of said microporous polyolefin support includes a plasma-, corona discharge- or ionizing radiation-induced graft copolymerization introducing proton-donating- or accepting groups (including R—OH, R—PO(OH)2, R—SO3H, R—COOH, R—NH2, 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole or R—N+R3).

37 . The membrane according to claim 35 , wherein said microporous polyolefin support has a surface of ozone or corona treated or ionized with any radiation method having a surface energy of at least 0.25 mN/m−2 but not more than 8.5 mN/m−2.

38 . The membrane according to claim 34 , wherein said proton accepting polymer is formed of a polybenzimidazole class polymer with a thickness of less than 15 μm, and said support layer is formed of a microporous polymer.

39 . A method for generating a membrane or a bilayer membrane according to claim 22 , the method comprising the following steps:
dissolving a polybenzimidazole class polymer in a suitable solvent or dimethylacetamide (DMAC) to form a polymer solution at a polymer concentration between 0.5 and 35 wt-%; and: a) casting onto a flat substrate or a glass plate followed by drying and curing of a film, release of said film from said substrate and hot-pressing it together with said support layer to form the bilayer membrane, or b) casting onto said support layer, followed by drying and curing of said film to form the bilayer membrane; or c) spraying onto said support layer, followed by drying and curing of said film to form the bilayer membrane.

40 . The method according to claim 39 , wherein said polymer solution includes a mixture of a pristine polybenzimidazole class polymer and a modified polybenzimidazole class polymer yielding a polymer blend after film formation.

41 . A redox flow battery, comprising a membrane according to claim 22 forming a membrane electrolyte.

42 . The redox flow battery according to claim 41 , wherein the redox flow battery is a vanadium redox flow battery, and said proton accepting layer has a thickness determining an amount and a direction of a net vanadium flux across the bilayer membrane.

Assignees

• Scherrer Inst Paul

Inventors

• Gubler Lorenz
• Oldenburg Fabio J
• Arndt Alexander

Classifications

• H01M50/403

  Manufacturing processes of separators, membranes or diaphragms · CPC title

• H01M50/489

  Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties · CPC title

• H01M50/449

  having a layered structure · CPC title

• Y02E60/50

  Fuel cells · CPC title

• H01M8/1023

  having only carbon, e.g. polyarylenes, polystyrenes or polybutadiene-styrenes · CPC title