United States Patent (15) 3,653,968 Louzos (45) Apr
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United States Patent (15) 3,653,968 Louzos (45) Apr. 4, 1972 (54) SOLID STATE ELECTROCHEMICAL 3,476,606 1 1/1969 Owens.......... ... 136/83. R CELLS 3,443,997 5/1969 Argue et al........................... 136/83 R (72) Inventor: Demetrios Vasilios Louzos, Rocky River, - FOREIGN PATENTS ORAPPLICATIONS Ohio 1,140,398 1/1969 Great Britain (73) Assignee: Union Carbide Corporation, New York, N.Y. Primary Examiner-Winston A. Douglas Assistant Examiner-C. F. Lefevour (22 Filed: May 4, 1970 Attorney-Paul A. Rose, John F. Hohmann, John R. Doherty (21) Appl. No.: 34,442 and Michael A. Caputo 57) ABSTRACT (52) U.S. Cl. ............................................ 136/83 R, 136/153 A solid state electrochemical cell having a silver or copper (5ll Int. Cl. ....................................................... H01m 21/00 anode, an iodine containing cathode and an electrolyte of the 58 Field of Search............................. 136783, 6, 20, 23, 153 general formula 56) References Cited MCN 4Ag UNITED STATES PATENTS wherein M is potassium, rubidium or cesium O a mixture 3,476,605 1 1/1969 Owens.................................. 136/83 R thereof. 19 Claims, 2 Drawing Figures Patented April 4, 1972 3,653,968 -0 a NSNZz" e 3242,SS: .264/ vote 622222r. aSilver Abazaavazoza2 Zg&4%.S. 2xxxiii.2522. SSSSKSK23S 23S 2 assassys S13 As % 27sis amoazeazaay NVENTOR Aeneas AZazzas ATToRNE 3,653,968 2 SOLID STATEELECTROCHEMICAL CELLS and electrical contact would be made to the anode and cathode at opposite ends of the stack. This invention relates to solid state electrochemical cells, as FIG. 2 shows a more refined cells construction employing well as solid state batteries comprising an assembly of such additional parts, but the basic components of this cell, cells. generally designated 20, will function in much the same The vast majority of electrochemical cells presently in use manner as the three layers of the simplified cell of FIG. i. Cell are aqueous systems and are dependent upon the flow of ions 20 comprises an electrolyte layer 22, which is identical to through an aqueous solution of metallic salts. In the so-called electrolyte layer 14 of cell 10, having an anode assembly on 'dry cell' the aqueous solution is immobilized in a paste or one side thereof and a cathode assembly on the other side gelled mixture to overcome the difficulties associated with 10 thereof. handling and packaging a liquid. However, even after immo The anode assembly comprises a disc which is a pressed bilization, the system is still subject to possible leakage, has a silver powder anode 24 adjacent the electrolyte layer 22 and limited shelf life due to drying out or crystallization of the an anode collector 26 on the outside surface of anode 24. The salts, and is suitable for use only within a limited temperature collector can be any compatible electrically conductive range corresponding to the liquid range of the electrolyte. In 15 material, e.g., silver metal foil. addition, the necessity of including a large volume of immo The cathode assembly comprises a disc which is an iodine bilizing material has hindered the aims of miniaturization. containing pressed powder cathode 28, e.g., 2 perylene 3 Solid state electrochemical devices, i.e., those comprising components which are normally solids at ambient tempera iodine complex having a metallic cathode collector 30, e.g., a ture, have been known to the art for several years. However, thin sheet of nickel, on its outer surface. these cells have not achieved widespread use either because of The entire cell assembly is compressed during manufacture their low power output or the sensitivity of the various com to establish good electrical contact and a physical bond ponents to moisture. between the various layers and the cell is thereafter encapsu The low power output of these cells is due primarily to the lated in plastic 32 to form a sealed unit cell. The layers of low specific conductances of the various components. Most 25 plastic covering the anode collector 26 and cathode collector solids have specific conductances at room temperature (20 20 may be punctured (not shown) to allow external contact to C.) in the range of 10 to 10 ohm cm as compared to be made with the cell, e.g., by filling the punctures with a con aqueous solutions of salts which nominally have a specific ductive epoxy sealer. conductance of 0.5 to 0.8 ohm cm. Each of the cell components and their method of manufac The sensitivity of the cells to moisture is due primarily to the 30 ture will be described in greater detail in the ensuing discus reactivity and degradation of the solid electrolyte in the SO1. presence of water, even the moisture contained in the at mosphere. THE ANODE U.S. Pat. application Ser. No. 805,002, filed Mar. 6, 1969, by G. W. Mellors, now abandoned, describes novel com 35 The choice of an anode for a solid state battery is dependent pounds and mixtures of compounds which are solid ionic con upon the mechanism through which the solid electrolyte ductors at room temperature and have specific conductances operates. The electrolytes of the present invention conduct sufficiently high to permit their use in practical battery appli primarily through transport of metal ions and the only metal cations. In addition, many of these compounds are less sensi 40 ions which are transported at a sufficient rate to be useful in tive to moisture than those which have previously been availa electrochemical cells are silver and copper. For this reason the ble. only anodes useful in cells of the present invention are those It has now been found that the combination of a silver or containing silver or copper. copper anode with the electrolytes of U.S. Pat. application The anode metal may be present as a thin metal foil or layer Ser. No. 805,002 and specific solid iodine containing com 45 of metal deposited on the electrolyte or may be a compressed pounds having at least a fraction of an iodine atom at a layer of the powdered metal. Preferably, the pressed powder valence of zero as a cathode yield solid state cells which dis layer is used since it provides a larger surface area at the play good shelf life stability and are powerful enough for prac anode-electrolyte interface, permits more intimate contact tical battery applications. between the anode and electrolyte layers when pressed The invention will be more particularly described with 50 together, and permits the incorporation into the anode layer reference to the accompanying drawings in which: of particles of electrolyte, binder or carbon which have all FIG. is a cross-sectional view of an idealized solid state been shown to improve cell performance. cell in accordance with the present invention; and A preferred anode mixture can be prepared from silver FIG. 2 is a cross-sectional view, partially cut-away, of a powder mixed with powdered electrolyte, acetylene black and preferred packaged solid state cell in accordance with the in 55 vention. graphite. These components are first dried over phosphorus Referring in more detail to FIG. 1, there is shown a solid pentaoxide in a nitrogen atmosphere and mixed to form a state cell, generally designated 10, formed of three layers, an uniform composition. A typical preferred formulation would anode 12, an electrolyte layer 14 and a cathode 16, each be 0.70 gram silver powder, 0.15 gram electrolyte, 0.05 gram shown in nonscaler, simplified form. The anode 12, in the sim graphite and 0.001 gram acetylene black. plest embodiment of the invention, is a layer of metallic silver It has been found that by using a fine silver powder the which may be a thin sheet of silver foil or a thin layer of silver capacity of the cell is substantially increased. This improved metal deposited on one side of electrolyte layer 14. The elec performance is probably due to the resulting increased surface trolyte layer 14 is a thin disc formed by compressing powdered area of the anode-electrolyte interface. It has been found, for electrolyte, e.g., monopotassium tetrasilver tetraiodide mono 65 example, that by using silver powder of 0.9-1.4 micron in cyanide (KAgCN). The cathode 16 is also a pressed powder diameter the capacity of the cell is 2% times greater than that disc formed from an iodine containing compound or complex, of a cell using 5-8 micron silver powder. The most preferred e.g., 2 perylene 3 iodine. The three layers of cell 10 are held silver powder has a discrete particle size in the range of together by intimate contact between the particles at the inter 0.9-1.4 micron. faces between the various layers which is achieved by com For certain applications a large cell capacity is not required pression at the time of manufacture. Thereafter, the cell will and the amount of silver or copper in the anode may be function without external pressure being applied. kept to a minimum to reduce the cost of the cell. In such To operate cell 10 it is merely necessary to make electrical instances it has been found desirable to employ an anode contact to the anode 12 and the cathode 16. If desired, several comprising a thin coat of silver or copper on a substrate. e.g. cells can be formed into a stack in the conventional manner 75 a high surface area graphite and/or acetylene black substrate. 3,653,968 3 4 The silver or copper may conveniently be adhered to the formation of the novel compounds according to the invention substrate by vacuum deposition followed by compression.