United States Patent [191 [11] 4,298,664 Joshi et al. [45] Nov. 3, 1981

[54] -CONTAINING SOLID STATE [56] References Cited ELECT ROLYTE U.S. PATENT DOCUMENTS [75] Inventors: Ashok V. Joshi, Fishkill; Arun D. 3,837,920 9/1974 Liang et al...... 429/191 Jatkar, Goshen, both of N.Y.; William P. Sholette, Warminster, Pa. Primary Examiner—Charles F. LeFevour [73] Assignee: Ray-O-Vac Corporation, Madison, Attorney, Agent, or Firm-Raymond J. Kenny; Francis Wis. J. Mulligan, Jr. [21] Appl. No.: 200,277 [57] ABSTRACI‘ [22] Filed: Oct. 24, 1980 An electrolyte for a solid state lithium electrochemical cell comprising an interdiffused mixture of P13 or B13 [51] Int. Cl.3 ...... H01M 6/18 and LiI and optionally A1203 and cells containing such [52] US. Cl...... 429/191; 429/ 193; 429/199; 252/ 62.2 electrolyte. ~ [58] Field of’ Search ...... 429/ 191, 193, 199; 423/300; 252/ 62.2, 182.1 11 Claims, No Drawings 4,298,664 1 2 electrolyte can contain small amounts of other materials PHOSPHORUS-CONTAINING SOLID STATE miscible with the interdiffused mass. These materials ELECT ROLYTE include impurities normally associated with commer cially available phosphorus , triiodide The present invention is concerned with solidstate and lithium . In general, however, inclusion of batteries and, more particularly, with an improved lith such materials is not desirable but rather the result of ium ion transport electrolyte for solid state batteries. inevitable contamination which occurs in manufactur HISTORY OF THE ART AND PROBLEM ing processes. It is advantageous to maintain the amount of phos In order to produce a high energy density solid state H 0 phorus triiodide in the electrolytes of the present inven battery, it is necessary to provide not only high energy tion in the range of about 2 to about 12 mole percent. density anodes and cathodes but also an effective ion The electrolyte of the present invention is made by transport electrolyte. The electrolyte mustbe an elec thoroughly blending appropriate amounts of phospho tronic insulator and an electrolytic conductor. Among rus triiodide or boron triiodide and pow the number of solids which satisfy these criteria at room 5 ders, heating the blended powders in an inert atmo temperature, solid lithium iodide is known to be advan sphere at a temperature in excess of the of tageous in that it has the capability of providing electro phosphorus triiodide (61° C.) or boron triiodide (43° C.) lytic conduction by the transport of lithium ions. This for a time sufficient to thoroughly interdiffuse the two permits lithium, the most energy dense of the alkali materials, cooling the resultant interdiffused blend and metals, to be used as an anode. However, the electro 20 grinding to form a ?ne powder product. More particu lytic conductivity of pure lithium iodide is only about larly, heating for one half hour at temperatures in the 1O~7 (ohm-cm)-1. To be useful, even in low drain mi range of 150° C. to 200° C. has been found to be ade croelectronic applications, the electrolytic conductivity quate to provide the phosphorus triiodide-containing must be increased by at least an order of magnitude. interdiffused mixture of the present invention. Without increasing the electrolytic conductivity of a 25 Table I sets forth exemplary electrolytes of the pres lithium iodide electrolyte, a cell inclusive of such an ent invention made by the process described in the electrolyte is likely to have extraordinarily high internal previous paragraph. ' resistance and a high potential drop for a given drain rate. TABLE I This problem has been recognized and solutions have Conductivity ,. been proposed. For example, in U.S. Pat. No. 3,837,920, Example No. LiI (mole %) P13 (mole %) (ohm-emfl ' it has been proposed to add to a lithium iodide matrix a I 95 s 3.5 X 10-6 material from the group of calcium iodide, oxide and II 92 2 2.6 X 10-6 chloride, barium iodide and oxide,'beryllium iodide and III 92.4 7.6 2.7~>< 10-6 chloride, magnesium iodide and chloride, barium chlo IV 85 15 9.3 >< 10~7 ride and strontium iodide and chloride. This proposal is not totally satisfactory in that the metal ions in materials In addition to phosphorus triiodide, lithium iodide mentioned in the prior art are reducible to the metallic and associated impurities and incidental ingredients, the state by lithium and thus present the possibility of pro electrolytes of the present invention can contain up to ducing electronic shorting across the electrolyte be 40 about 60 mole percent of alumina. In particular, boron tween the anode and the cathode. triiodide is a useful ingredient in compositions contain ing alumina. This alumina can be ground into the PI3- or DISCOVERY AND OBJECT OF THE BI3-LiI mixture prior to interdiffusion or the interdif INVENTION fused mass without alumina can be ground to a powder, It has now been discovered that a composition of 45 mixed and ground with alumina‘powder and subjected matter comprising an intimate, heat-treated interdif to a second interdiffusion. Considering the alumina fused mixture of lithium iodide and either boron triio content, the electrolytes of the present invention con dide or phosphorous triiodide can provide a novel elec tain, in mole percent, about 0.4% to about 16% of phos trolyte characterized by relatively high electrolytic phorus and/or boron triiodide and advantageously conductivity, very low electronic conductivity and about 0.8% to about 12% phosphorus triiodide, about freedom from the electronic shorting possibility and is 33% to about 99% lithium iodide and up to about 60% thereby suitable for use in a high energy density solid aluminum oxide. Note that although this speci?cation state cell using lithium or lithium-rich alloys as the and claims are written in terms of the electrolytes con anode and conventional materials as the cathode. taining P13, B13, A1203 and Lil, this wording is not An object of the present invention is to provide a intended to imply that during interdiffusion there may novel, solid state lithium iodide-based electrolyte. not be some interreaction among the ingredients. The Another object of the invention is to provide a novel language employed merely implies that the materials solid state electrochemical cell containing the novel used to make the electrolytes are present, albeit perhaps electrolyte of the present invention. changed in specie, in the ?nal electrolyte. Other objects and advantages will become apparent 60 Examples of alumina-containing compositions are as from the present description. follows: PARTICULAR DESCRIPTION OF THE TABLE II INVENTION LiI PI3/BI3 - Al2O3 Conductivity . EX. N0. (mole %) (mole %) (mole %) (ohm-cm)"l The novel electrolyte of the invention essentially 65 comprises an interdiffused mass of about 1 to about 16 v 88.2 1.8 P13 10 2.0 x 10~5 v1 25.5 4.5 P13 10 8.6 >< 10—6 mole percent of phosphorus triiodide or boron triiodide VII 72.4 1.6 P13 20 2.6 x 10-5 with the balance being essentially lithium iodide. The vm 76 4.0 P13 20 1.3 X 10~5 4,298,664 3 4 TABLE II-continued sidered to be within the purview and scope of the inven tion and appended claims. Lil PI3/BI3 A1203 Conductivity Ex. No. (mole %) (mole %) (mole %) (ohm-emf] We claim: 1. A solid state electrolyte comprising an interdif 1x , 68.6 1.4 PI3 30 5.0 X 10-5 x 66.5 3.5 P13 30 3.7 >< 10-5 fused mixture of, in mole percent, about 0.4% to about XI 63.2 1.3 PI3 35 5.2 >< 10—5_ 16% of a material selected from the group of boron _1.5 >< 10-“ triiodide and phosphorus triiodide, about 33% to about x11 57 3.0 P13 40 3.7 X 10-5 99% lithium iodide and up to about 60% alumina. x111 49 1.0 P13 50 5.1 >< 10—5 XIV 73.5 1.5 BI3 25 1.2 >< 10-5 2.'A solid state electrolyte as in claim 1 containing xv 63.7 1.3 B13 35 5.5 >< 1'0-5 phosphorus triiodide. XVI 53.9 1.1 1313 45 1.1 >< 10-4 3. A solid state electrolyte as in claim 1 comprising, in ‘The range represents results obtained from various samples made with H51 grade mole percent, about 0.8% to about 12% phosphorus alumina supplied by Alcoa in which ?neness of grind of the alumina granules was triiodide. varied. Higher conductivities are obtained with electrolytes made with more ?nely ground alumina. 4. A solid state electrolyte as in claim 1 containing 15 boron triiodide and alumina. . Table II shows that compositionscontaining, in mole 5. A solid state electrolyte as in claim 1 which con percent, about 35% to about 45% alumina, about 50% tains, in mole percent, about 50% to about 65% lithium to about 65% lithium iodide and about 1% to about iodide, about 1% to about 1.5% of material selected 1.5% of either boron triiodide or phosphorus triiodide from the group of boron triiodide and phosphorus triio are particularly advantageous in exhibiting high electro dide and about 35% to about 45% alumina. lytic, lithium ion transport conductivity. Examples of 6. A solid state electrolyte comprising an interdif the electrolytes of the present invention can be used in fused mixture of about 1 to about 16 mole percent phos solid state electrochemical cells using lithium metal as phorus triiodide with the balance being essentially lith the anode and a wide variety of compatible cathode ium iodide. ' materials. Suitable cathodes, mounted on a cathode ,7. A solid state electrolyte as in claim 6 wherein the current collector or packed in one portion ofa button mole percent of phosphorus triiodide is in the range of about 2% to 12%. cell, include materials such as mixtures of bismuth tri bromide, titanium disul?de and bismuth, bismuth tribro 8. A solid state electrochemical cell having a lithium mide, titanium disul?de and , and an iodine ad anode, a solid state electrolyte comprising an interdif duct with poly-2-vinylpyridine, with or without ad fused mixture of, in mole percent, about 0.4% to about 16% phosphorus triiodide, about 33% to about 99% mixed electronic conductivity enhancers. An example lithium iodide and up to about 60% alumina and a com of solid state cell using the novel, solid electrolyte of the patible cathode. present invention is now given. 9. A solid state electrochemical cell as in claim 8 EXAMPLE XIV 35 wherein the electrolyte contains, in mole percent, about 0.8% to about 12% phosphorus triiodide. A solid state cell employing the electrolyte of Exam 10. A solid state electrochemical cell as in claim 8 ple I, a lithium anode and a cathode comprising a mix wherein the electrolyte contains, in mole percent, about ture of, by weight, BiBr3, T182 and I; had an open cir 63% lithium iodide, about 1.3% phosphorus triiodide cuit potential at 37° C. of 2.81 v and an initial discharge 40 and about 35% alumina. , . voltage of 2.71 v under a 120 kilo-ohm external load. 11. A solid state electrochemical cell as in claim 8 Although the present invention has been described in wherein the electrolyte contains, in mole percent, about conjunction with preferred embodiments, it is to be 50% to about 65% lithium iodide, about 1% to about understood that modi?cations and variations may be 1.5% of a material from the group of phosphorus triio resorted to without departing from the spirit and scope 45 dide and boron triiodide and about 35% to about 45% of the invention, as those skilled in the art will readily of alumina. understand. Such modi?cations and variations are con * * * * *

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