Patent Publication Number: US-3879219-A

Title: Sealed primary sodium-halogen cell

Description:
United States Patent 1 Farrington Apr. 22, 1975 SEALED PRIMARY SODIUM-HALOGEN CELL [75] inventor: Gregory C. Farrington, Clifton Park, NY.  
 [73] Assignee: General Electric Company,  
 Schenectady, NY.  
 [22] Filed: Mar. 18, 1974 [21] Appl. No.: 451,964  
 [52] US. Cl 136/83 R [51] Int. Cl. l-l0lm 13/00 [58] Field of Search 136/83 R, 20. 100, 6 LN, 136/6 FS, 153  
 [56] References Cited UNITED STATES PATENTS 3.703.415 11/1972 Mitoffctal. 136/83 R 3,730,771 5/1973 Tanncnbcrger ct al... 3.762.955 10/1973 Dubin 136/83 R 3.773.558 11/1973 Charbonnier ct al. 136/100 R 2/1974 Hess 136/83 R 6/1974 Mitoff 136/83 R Primary E.\&#39;aminer.lohn H. Mack Assistant Examiner-C. F. Lefevour Attorney, Agent, or FirntPaul R. Webb, ll; Joseph T. Cohen; Jerome C. Squillaro [57] ABSTRACT 4 Claims, 1 Drawing Figure SEALED PRIMARY SODIUM-HALOGEN CELL This invention relates to sealed primary sodiumhalogen cells and. more particularly. to such cells employing a cathode of an anhydrous mixture of bromine and a specific salt.  
  Sodium-halogen cells are known in the prior art as. for example, described in Hess US. Pat. No. 3.793.080 issued Feb. 19. I974 under the title Sealed Primary Sodium-Halogen Battery With Bromine-Iodine Mixture. This patent describes and claims such a battery in which the cathode comprises a mixture of bromine and from 5.0 to 60 weight percent of iodine with specific conductive material, additives or both. The subject patent is assigned to the same assignee as the present application.  
  The primary object of my invention is to provide a primary battery which has a near zero self-discharge rate, high cell voltage and high energy density.  
  In accordance with one aspect of my invention, a sealed primary sodium-halogen cell comprises a casing. an anode positioned in the casing, the anode selected from the class consisting of sodium. sodium as an amalgam. and sodium in a nonaqueous electrolyte. a solid sodium ion-conductive electrolyte positioned in the casing adjacent the anode, and a cathode positioned adjacent the opposite side of the electrolyte, the cathode comprising an anhydrous mixture of a salt selected from the class consisting of triand tetraalkylammonium chlorides and bromides. and bromine.  
  These and various other objects, features and advantages of the invention will be better understood from the following description taken in connection with the accompanying drawing in which:  
  The single FIGURE is a sectional view of a battery made in accordance with my invention.  
  In the single FlGURE of the drawing, there is shown generally at a sealed primary sodium-halogen cell embodying our invention which has a metallic casing 11 including an anode portion 12 and a cathode por tion 13. An anode 14 of sodium as an amalgam is shown positioned within anode portion 12. A cathode 15 comprising an anhydrous mixture of a specific salt and bromine positioned within cathode portion 13. A solid sodium ion-conductive electrolyte 16 is positioned between and adjacent anode l4 and cathode 15. Electrical leads (not shown) are affixed to the respective casing portions. Closed fill tubes 17 and 18 are associated with the respective portions 12 and 13. Electrolyte 16 is secured on opposite sides to portions 12 and 13 by identical glass seals 19.  
  A sealed primary sodium-bromine cell is formed by providing a metallic casing, providing an anode within the casing, the anode selected from the class consisting of sodium, sodium as an amalgam, and sodium in a nonaqueous electrolyte. providing a solid sodium ionconductive electrolyte adjacent the anode, and providing a cathode adjacent the opposite side of the electrolyte. the cathode comprising an anhydrous mixture of a salt selected from the class consisting of triand tetraalkylammonium chlorides and bromides, and bromine. We found that such cells have an open circuit voltage of from 3.25 to 3.6 volts.  
  The anode may consist of sodium, a sodium amalgam or sodium in a nonaqueous solvent. The sodium amalgam can be in the range of compositions from about 95% sodium and 5% mercury by weight to about sodium and 65% mercury. For the fully charged state of the cell. the amalgam composition is preferably high in sodium. Cells using sodium amalgams cannot be used efficiently at temperatures below 21.5C due to complete freezing of the amalgam.  
  The use of nonaqueous electrolytes permits cell operation to much lower temperatures as determined by the freezing point of the electrolyte. A preferred electrolyte is propylene carbonate in which a sodium halide salt is dissolved. This electrolyte permits cell operation down to 0C.  
  The cathode somprises an anhydrous mixture of a salt selected from the class consisting of triand tetraalkylammonium chlorides and bromides. and bromine. Such a solution can contain bromine from 1.0 weight percent to 99.0 weight percent. and the salt from 1.0 weight percent to 99.0 weight percent. While various triand tetralkylammonium chlorides and bromides are suitable, I prefer to employ tetrabutylammonium bromide or tetraethylammonium chloride.  
  Bromine has an exceedingly low ionic conductivity for use as a cathode. I found unexpectedly that I could form a desirable cathode by forming an anhydrous mixture of a salt selected from the class consisting of triand tetraalkylammonium chlorides and bromides and bromine. Such solutions exhibit a conductivity in the range of l0&#39;-mho/cm at concentrations of approximately one molar. These cathodes are stable and do not appear to have any deleterious effect on the solid electrolyte.  
  The anode casing portion can be made of nickel. Kovar alloy, niobium or tantalum, while the cathode casing portion should preferably be niobium or tantalum. These metals have been shown to be chemically stable in their respective environments.  
  A method of hermetically sealing the anode and cathode portions of the casing to opposite sides of the solid electrolyte is described and claimed in copending patent application Ser. No. 148,793, filed June l, 1971, under the title Method of Forming a Metallic Battery Casing in the name of Stephan P. Mitoff. This copending application is assigned to the same assignee as the present application.  
  In the above method. a disc of solid sodium ionconductive electrolyte, for example, sodium betaalumina, has stacked thereon a ring of General Electric Company 1013 glass cut from tubing. The glass ring has approximately the inside and outside diameter of the cup lip of casing portion. On the glass ring is stacked the nickel anode portion in cup form with its lip adjacent the ring. The three components are positioned on a supporting jig and lowered into an inert atmosphere furnace at l,00OC for about one minute. The resulting seal is helium leaktight. The process is repeated to seal the cathode portion to the opposite surface of the solid electrolyte. Both anode and cathode portions can also be sealed simultaneously to the disc in the above manner. It will be appreciated that other cell configurations can be employed.  
  The anode portion can be filled with sodium, sodium as an amalgam or sodium in a nonaqueous electrolyte through tube 17 after which the tube is sealed, as for example, by welding. The cathode portion is filled with an anhydrous mixture of tetrabutylammonium bromide and bromine through tube 18, after which the tube is similarly sealed. The resulting device is a sealed, primary sodium-halogen cell. Leads (not shown) are attached to the respective casing portions for operation of the cell.  
  Examples of primary sodium-halogen cells made in accordance with my invention are set forth below:  
 EXAMPLES 1 AND 2 Two vented cells were constructed each of which employed a glass casing consisting of an anode portion and a cathode portion. A platinum wire extended into each casing portion. The portions were separated by a solid sodium beta-alumina electrolyte disc. The anode portion of each cell was then filled with a sodium amalgam of a composition of 70 weight percent of sodium and 30 weight percent of mercury. An anhydrous mixture of tetrabutylammonium bromide and bromine was added to the cathode portion of Cell I. An anhydrous mixture of tetraethylammonium chloride and bromine was added to the cathode portion of Cell II. The resulting devices were primary sodium-halogen cells. Open circuit voltages of 3.25 and 3.6 volts, respectively, were obtained.  
 EXAMPLE 3 The cells of Examples 1 and 2 exhibited at C the following polarization behavior which is shown below in Table I.  
 &#39; Cell ll Voltage- Current Density- Volts ma/cm While other modifications of the invention and variations thereof which may be employed within the scope of the invention have not been described, the invention is intended to include such as may be embraced within the following claims.  
  What I claim as new and desire to secure by Letters Patent of the United States is:  
  l. A sealed primary sodium-halogen cell comprising a casing, an anode positioned in the casing, the anode selected from the class consisting of sodium, sodium as an amalgam, and sodium in a nonaqueous electrolyte, a solid sodium beta-alumina ion-conductive electrolyte positioned in the casing adjacent the anode, and a cathode positioned adjacent the opposite side of the electrolyte, the cathode comprising an anhydrous mixture of a salt selected from the class consisting of triand tetraalkylammonium chlorides and bromides, and bromine.  
  2. A sealed primary sodium-halogen cell as in claim 1, in which the bromine is present from 1.0 weight percent to 99.0 weight percent, and the organic salt is present from 1.0 weight percent to 99.0 weight percent.  
  3. A sealed primary sodium-halogen cell as in claim 1, in which the salt is tetrabutylammonium bromide.  
 4. A sealed primary sodium-halogen cell as in claim 1, in which the salt is tetraethylammonium chloride.