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(12) Patent Application Publication (10) Pub. No.: US 2010/0196768 A1 Roberts Et Al US 2010.0196768A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2010/0196768 A1 Roberts et al. (43) Pub. Date: Aug. 5,9 2010 (54) ELECTROLYTE MANAGEMENT IN Related U.S. Application Data ZNCAAR SYSTEMS (60) Provisional application No. 60/926,618, filed on Apr. (76) Inventors: Gregory Roberts, Oakland, CA 27, 2007. (US); Irfan Rehmanji, Vancouver Publication Classification (CA) (51) Int. Cl. Correspondence Address: HOLM 8/22 (2006.01) CHERNOFF, VILHAUER, MCCLUNG & STEN- (52) U.S. Cl. ........................................................ 429/406 ZEL, LLP (57) ABSTRACT 601 SW Second Avenue, Suite 1600 PORTLAND, OR 97204-3157 (US) A Zincfair system such as a fuel cell or mechanically rechargeable Zincfair battery has a Zincate-trapping material (21)21) AppAppl. No.: 12/451,1679 to extend electrolvtey life. Solid calcium hydroxidey is used as the Zincate-trapping material in some embodiments. The Zin (22)22) PCT Fled: Apr.pr 25,AS, 2008 cate-trappingpp1ng material mayy bebe pprovided in the form of ppellets, powders, or the like in assemblies that permit electrolyte to (86). PCT No.: PCT/USO8/OS334 contact the Zincate-trapping material. The assemblies may be replaceable while the system remains in operation. In some S371 (c)(1), embodiments, the assemblies are removable and may be pro (2), (4) Date: Mar. 30, 2010 cessed after use to collect Zinc for recycling. * 33 X xxi-xx-x-x-xx-xx-xxx; s: --------------------- -xxxx Patent Application Publication Aug. 5, 2010 Sheet 1 of 4 US 2010/0196768A1 8 :8 Patent Application Publication Aug. 5, 2010 Sheet 2 of 4 US 2010/0196768A1 Patent Application Publication Aug. 5, 2010 Sheet 3 of 4 US 2010/0196768A1 33A OOOOOOOOOOOOOOOOOOOOOXanxiou?ness OOOOOOOOOOOOOOOOOOOOOan data SSs SSSSSSSSSSn 5 O O OCC OOOOOO SS.CC. OOC FIGURE 2A Patent Application Publication Aug. 5, 2010 Sheet 4 of 4 US 2010/0196768A1 US 2010/0196768 A1 Aug. 5, 2010 ELECTROLYTE MANAGEMENT IN Solutions: A Structural Study, Journal of the Electrochemical ZNCAAR SYSTEMS Society, Vol. 142, No. 5, May 1995, p. 1359. 0009. The high solubility of the zincate ion in alkaline REFERENCE TO RELATED APPLICATION Solutions causes longevity and reliability problems in second 0001. This application claims priority from U.S. patent ary zincfair batteries. The issues of zinc dendrite formation, application No. 60/926,618 filed on 27 Apr. 2007 and entitled which can cause cell shorting, and anode shape change due to ELECTROLYTE REMEDIATION IN ZINC-AIR FUEL preferred locations for the deposition of zinc, are well known CELLS. For purposes of the United States of America, this in the field. One attempted solution is to use a solid-phase application claims the benefit under 35 U.S.C. S 119 of U.S. material that can remove tetrahydroxozincate ions from solu patent application No. 60/926,618 filed on 27 Apr. 2007, tion by chemical reaction. Calcium hydroxide is often pre which is hereby incorporated herein by reference. ferred as the material for scavenging Zincate ions. Calcium hydroxide can react with the soluble zincate ion to form TECHNICAL FIELD calcium Zincate, a Solid phase with low solubility in alkaline 0002. This invention relates to electrochemical cells. The electrolytes, by the following reaction: invention has particular application to Zincfair-based fuel cells and mechanically rechargeable batteries with circulat ing electrolytes. The Solid phase is also referred to as a Zincate, and it is BACKGROUND common practice to refer to the solid phase by its full name 0003 Electrochemical zincfair cells have zinc-based (e.g., calcium Zincate or magnesium Zincate from reaction negative electrodes, referred to as anodes in primary cells, and with magnesium hydroxide) to avoid confusion with the gas-diffusion positive electrodes, referred to as cathodes in soluble Zincate ion. primary cells. Such cells electro-catalytically reduce oxygen 0010 Calcium hydroxide powder is often incorporated from air. The electrolyte is typically a concentrated solution directly into the negative electrode along with Zinc, binders, of potassium hydroxide (KOH) or sodium hydroxide (NaOH) and other materials. U.S. Pat. No. 4,358,517 discusses using in liquid or gel form. a certain ratio of calcium hydroxide to Zinc active material for 0004 Zincfair batteries and fuel cells are commercially a nickel/zinc secondary battery for this purpose. U.S. Pat. No. appealing for several reasons. Zinc is an attractive anode 5,863,676 advocates using calcium Zincate, the material material because it is abundant, has a low equivalent weight, formed by the reaction of zincate ions with calcium hydrox has a low standard reduction potential in the electrochemical series, and is environmentally favorable compared to alterna ide, directly as the active material in a secondary battery. U.S. tives like cadmium. A zincfair battery or fuel cell can have a Pat. Nos. 3,873,367 and 3,516,862 describe using calcium relatively small weight and Volume because a reactant, oxy hydroxide for these purposes in sealed, electrically-recharge gen, can be obtained from atmospheric air instead of being able cells. U.S. Pat. Nos. 3,516,862; 2,180,955; 3,497.391; stored for use. and 3,873.367 discuss integrating calcium hydroxide in 0005 Zincfair fuel cells and mechanically rechargeable sealed Zinc batteries. U.S. Pat. No. 3,873,367 discusses the batteries can be replenished by adding zinc and by either use of magnesium hydroxide in addition to calcium hydrox replacing the electrolyte, which accumulates reaction prod ide. U.S. Pat. No. 4,054,725 discusses using calcium hydrox ucts during cell operation, or by removing dissolved reaction ide within a zincfair battery to remove carbonate ions intro products from the electrolyte. duced as carbon dioxide from unscrubbed air is fed through 0006. In a zinc/air cell, the anodic reaction is commonly the air cathode and dissolved into the electrolyte. written as: 0011 Zincfair fuel cells and mechanically rechargeable batteries have electrolyte-related challenges. If the Zinc and air reactants can be Supplied continuously to a fuel cell, the 0007. In concentrated alkaline electrolytes, the tetrahy only limitation in operating time will be the degradation of droxozincate ion (Zn(OH)) is highly soluble. It is com electrolyte performance as reaction products accumulate in monly referred to as the Zincate ion. Zinc oxide can precipi the electrolyte. The reaction that generates Zincate ions from tate by the following reaction: anodically dissolved Zinc consumes hydroxide ions, which Zn(OH)2->ZnO+HO+2OH (2) adversely impacts fuel cell performance by lowering the ionic conductivity of the electrolyte and increasing concentration The cathodic reaction is given by: polarization. If the cell conditions and electrolyte chemistry 'AO+HO+2e->2OH (3) allow for Zinc oxide precipitation, the precipitation reaction 0008 Anodically dissolved zinc can form supersaturated will release hydroxide ions but may cause other problems. solutions with concentrations well beyond the equilibrium Precipitated zinc oxide can lower electrical conductivity by concentration in alkaline solutions (see e.g., F. R. McLarnon coating metallic particles and current collectors, clogging and E. J. Cairns, The Secondary Alkaline Zinc Electrode, pores in electrodes and separators, and affecting components Journal of the Electrochemical Society, Vol. 138, Issue 2, p. in systems with circulating electrolytes. The electrolyte will 645). Electrolyte additives, such as silicate salts, can be used eventually need to be replaced or regenerated because of the to stabilize the Supersaturated Solutions and retard Zinc oxide accumulation of reaction products. The electrolyte can be precipitation. Details about the differences between super regenerated by plating dissolved Zinc, but this is not possible saturated and undersaturated Zincate solutions in alkaline or desirable for all systems and applications. electrolytes are described in C. Debiemme-Chouvy, J. Vedel, 0012 Despite the work that has been done in this field, M. Bellissent-Funel, and R. Cortes, Supersaturated Zincate there remains a need for practical ways to extend the useful US 2010/0196768 A1 Aug. 5, 2010 electrolyte life and/or improve the performance characteris Accordingly, the description and drawings are to be regarded tics of zinc/air fuel cells and mechanically rechargeable bat in an illustrative, rather than a restrictive, sense. teries. 0025. Example embodiments of the invention provide ways to remove Zincate ions from the electrolyte in Zincfair SUMMARY fuel cells and mechanically rechargeable batteries that use circulating alkaline electrolytes. This description describes 0013 The present invention has a number of aspect. One example Zincate-trapping materials (which may be called aspect of the invention provides Zincfair systems such as Zincate Scavengers), example physical forms for the trap primary batteries, fuel cells, and/or mechanically recharge ping materials, example Zincfair systems and example meth able batteries that use continuously or intermittently circulat ods to incorporate Zincate-trapping materials in Zincfair sys ing alkaline solutions as an electrolyte. Other aspects of the tems having circulating electrolytes. invention relate to methods for operating and/or methods for maintaining Zincfair primary batteries, fuel cells, and/or Zincate-Trapping Materials mechanically rechargeable batteries. 0014. An example aspect of the invention provides a 0026 Calcium hydroxide is a suitable material to address
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