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J»JEuropaisches European Patent Office (jî) Publication number: 0 065 821 Office européen des brevets B 1

© EUROPEAN PATENT SPECIFICATION

® Date of publication of patent spécification: 10.07.85 (§) Int. Cl.4: C 01 D 15/04, H 01 M 6/18, H 01 G 9/02 (2J)rth Applicationa r ♦@ number:u 82302087.0mMM„„ (22) Date offiling: 23.04.82

® Lithium compounds.

(§) Priority: 27.04.81JP 62381/81 ® Proprietor: Hitachi Maxell Ltd. No 1-1-88, Ushitora Ibaraki-shi Osaka-fu(JP) @ Date of publication of application: 01.12.82 Bulletin 82/48 @ Inventor: Gotoh,Akira Misuzuso 5-go, 1 8-5 Masashidai-2-chome (§) Publication of the grant of the patent: Fuchu-shi (JP) 10.07.85 Bulletin 85/28 Inventor: Obayashi, Hidehito 8-24, Shimoshakujii-6-chome Nerima-ku Tokyo (JP) (M) Designated Contracting States: Inventor: Nagai, Ryo CHDEFRGBLINL 171, Kitanagaicho Nara-shi (JP) Inventor: Mochizuki, Shouji (a) References cited: Senrigarden-Haitsu 1420, 6-1 Yamadanishi-4- DE-A-2901303 chome GB-A-2 048 839 Suita-shi (JP) GB-A-2 062345 Inventor: Kudo, Tetsuichi 17-5, Oyamadai-2-chome m Setagaya-ku Tokyo (JP)

CM (7?) Representative: Ford, Michael Frederick et al CO MEWBURN ELLIS & CO. 2/3 Cursitor Street London EC4A1BQ (GB) m (0 o o Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall CL be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been LU paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. halide) and lithium imide, and is produced by mixing specified amounts of the two component This invention relates to lithium compounds, substances with each other and heating the and particularly to lithium compounds which resulting mixture at at least 300°C in an inert gas have high lithium ionic conductivity and are or hydrogen atmosphere. useful as lithium ionic conductive solid elec- Lithium imide, Li2NH, can be prepared by the trolytes. method reported by B. A. Boukamp et al (Phys. A variety of lithium compound have been Lett. 72A, 464 (1979)). considered as highly promising materials for use In this method, lithium nitride (Li3N) is heated, as lithium ionic conductors on an industrial basis. for example, at 500°C for about 30 min in a Thus, when a solid lithium ionic conductor is used gaseous 50/50 mixture of nitrogen and hydrogen, in various types of electrochemical devices, there to obtain Li2NH by the following reactions (1) and may be obtained following several characteristic (2). features that could not be attained in the past. For example, there will be no fear of leak or salting of electrolyte, the device can be used for a longer period of time and can have a much smaller and thinner configuration. Therefore, solid lithium ionic conductors are expected to have a number To bring the reaction (2) to completion, it is of applications such as very thin type cells and useful to conduct further heating in nitrogen at electrochromic displays. about 600°C for about 3 hours. When such a solid electrolyte is used for a cell A product obtained in this way was filled in or the like, it must meet several requirements. glass capillaries and the product was identified by However, hitherto there have not feen found any the X-ray powder diffraction method (the Debye- lithium compound that can meet all these require- Scherrer method) to confirm the formation of ments, and there is a keen demand for the Li2NH. availability of a lithium compound which has a Each of predetermined amounts of the thus sufficient lithium ionic conductivity at room obtained LiZNH was intimately mixed with a temperature. predetermined amount of LiCI, LiBr or Lil to form GB-A-2048839 describes lithium ionic a number of different mixtures. Each of the conductive solid electrolytes formed by reacting mixtures was pressure-molded into a disk-shaped together two or more binary lithium compounds, pellet using a die of 15 mm in diameter and a in particlular lithium nitride and lithium halide, at molding force of 2 tons. All the operations such as elevated temperatures. mixing of raw materials and molding of each This invention provides a novel lithium com- mixture were carried out in a nitrogen atmos- pound and solid electrolyte which have an phere. In addition, since LiBr contained water, it improve lithium ionic conductivity, which we was previously dehydrated by a prethermal treat- regard as sufficient. This invention is set out in the ment carried out in nitrogen gas at 400°C for 15 claims. hours. The invention will be further explained and Then, the resulting pellets were heat-treated in illustrative embodiments thereof given by way of a nitrogen atmosphere at 400-5000C for 30 hours example with reference to the drawings, in which to produce six kinds of compounds. Figures 1, 2 and 3 are diagrams each showing Each of the compounds thus obtained was the relationship between the species of the analyzed by the X-ray powder diffraction method compound of this invention and the term "y" to determine the d-value (interplanar spacing) which denotes the molar fraction of lithium imide and the relative intensity I/lo. The results are present in the compound. shown in Table 1, in which X represents the Figure 4 is a diagram showing the Arrhenius species of halogen in the lithium halide used as plots for the ionic conductivity of the compounds raw material, and y denotes the molar fraction of of this invention. lithium imide in the general formula The compound according to this invention is yLi2NH . (1-y)LiX which represents the composed of a lithium halide (herein LiCI, LiBr compound of this invention. and Lil are generically referred to as lithium

The d-values and relative intensities for Li2NH, unidentified crystal structure was from about 0.25 LiCI, LiBr and Lil used as raw materials are to about 0.55. When y was decreased to 0.15, an reported respectively on ASTM Cards 6-0417, LiBr phase appeared and, on the other hand, 4-0664, 6-0319 and 1-0592. However, the when y was 0.6 or larger, a phase of Li2NH results shown in Table 1 are entirely different coexisted with the matrix. from the values listed on the ASTM Cards. This Figure 3 shows the results for the case of X=I, difference confirms that novel compounds were in which the symbols 0 and• indicate that the formed by the process described above. compound yLi2NH. (1-y)Lil could exist stably When the d-values for the compounds 2, 3, @ with face centered cubic (fcc) structure having a and @ in Table 1 were calculated assuming the lattice constant of 9.45 A and of 10.36 A, respec- compounds to be of cubic lattice types having the tively. The symbol indicates that one lattice lattice constant a of 5.16, 8.86, 9.45 and 10.36 A type predominated over the other. respectively, the resulting d-values agreed very It was recognized that the compound closely with the measured values shown in Table yLi2NH . (1-y)Lil could exist stably as one having 1 and, moreover, the Miller indices obtained by face centered cubic (fcc) structure when y was in indexing showed a common regularity in all cases the range of about 0.33 to about 0.75. When y was of the compounds. 0.25 and when it was 0.85, a small but appreciable Namely, each of the diffraction lines for the amount of Lil and Li2NH, respectively, were found compounds 2, 3, @ and @ shown in Table 1 had to coexist with the matrix. the Miller indices h, k, I that were either all even or As described above, the lithium compound of all odd (in no case, an even number and an odd this invention is produced by mixing specified number were coexistent in a single set of the amounts of a lithium halide and lithium imide Miller indices). with each other and heating the resulting mixture. Accordingly, it was recognized that the lattice This reaction proceeds at a temperature of at types of the compounds 2, 3, @ and @ were all least about 300°C, and the reaction rate becomes face-centered cubic (fcc) and the values of the very high at temperatures of 350°C or higher. lattice constant a were 5.16 A, 8.86 A, 9.45 A and However, at a temperature of about 750- 10.36 A respectively. 800°C, although the lithium halide remains stable, On the other hand, the compounds 1 and @ in Li2NH will decompose. Therefore, it should be Table 1 had such complicated crystal structures avoided to heat the mixture to a temperature of that their lattice types could not be identified. 700-800°C or higher. Next, the above procedure was repeated while In addition, the reaction is carried out in an inert changing the values of X and y in the general gas such as nitrogen, argon and helium or in a formula set forth above, to ascertain the com- hydrogen atmosphere. When the reaction is con- positional ranges in which the compounds can ducted in a vacuum or at a reduced pressure, raw exist as stable ones. The results are shown in materials or reaction products will be more likely Figures 1, 2 and 3. In these Figures, the symbols to decompose. Therefore, it is preferable to carry C, B, I and N represent LiCI, LiBr, Lil and Li2NH, out the reaction at an atmospheric pressure or at respectively. a pressure approximate to it. Figure 1 shows the results for the case of X=CI, The compound of the above-mentioned general in which the symbols A and A indicate that the formula in which X is CI has a melting point compound yLi2NH . (I-y)LiCI was able to exist slightly varying in accordance with the value of y stably as single phase of unidentified structure but substantially within the range of about 490 to and as a single phase face-centered cubic (fcc), 600°C. Similarly, the melting points of the com- respectively. The symbol indicates that one pounds corresponding to X=Br and X=I, respec- crystal type phase predominated over the other. tively, are 450-460°C and 410-550°C. As is clear from Figure 1, when X is Cl, the When the compounds are heated to these compound can exist as a stable one, if y is in the respective temperatures, they are melted, and yet range of about 0.35 to about 0.98. they remain stable without decomposing. When y became 0.30, a considerable amount of However, when the temperature is raised to about LiCI was found to coexist and, on the other hand, 750-800°C or higher, the compounds will decom- when y exceeded 0.98, Li2NH was found to pose, which is considered to arise from the coexist. Therefore, the range of y in which the decomposition and the resulting escape or eva- compound can exist as a single one is about 0.35 poration of NH present in the ionic crystals to about 0.98, when X is Cl. constituting the compounds. Figure 2 shows the results for the case of X=Br, in which the symbols D and@ indicate that the Example 1 compound yLi2NH - (1-y)LiBr could exist stably Each of the above mentioned compounds 1 to with the crystal structure of face-centered cubic @ was molded into a disk-shaped pellet of 2 to 3 (fcc) lattice and of unidentified type, respectively. mm in thickness using a die of 10 mm in diameter The symbol + indicates that both types of crystal and a molding face of 2 tons. An electrode was were present in similar amounts. formed by uniformly dispersing Pb-added Pbl2 on As is clear from Figure 2, when X is Br, the one side of the disk-shaped compound, and the range of y in which the compound can exist stably whole was pressure-molded at a molding with face centered cubic (fcc) lattice or with an pressure of 2 tons to obtain a disk-shaped double- layer pellet consisting of a layer of the compound chlorine, about 0.25 to about 0.55 when X is and a layer of Pb-added Pb12. bromine, and about 0.33 to about 0.75 when X is A piece of metallic lithium was pressure- iodine. bonded to the other side of the pellet to form 2. A lithium compound according to claim 1 anode, whereby a cell having a structure of wherein X in said general formula is Cl. Pbl2(Pb) the above compound Li was obtained. 3. A lithium compound according to claim 1 When the e.m.f. of each of the cells thus wherein X in said general formula is Br. obtained was measured at room temperature, an 4. A lithium compound according to claim 1, e.m.f. of 1.90 V was obtained, which was coin- wherein X in said general formula is I. cident with the theoretical value. Thus, it was 5. Use of a lithium compound according to any confirmed that the compounds 1 to @ are lithium one of claims 1 to 4 as an ionic conductive solid ionic conductors useful as solid electrolytes. electrolyte. 6. A cell comprising a lithium ionic conductive Example 2 solid electrolyte with electrodes provided respec- Each of the compounds 1 to @ was molded tively on two sides thereof, said solid electrolyte into a disk-shaped pellet of 2 to 3 mm in thickness consisting of a lithium compound according to using a die of 10 mm in diameter and a molding any one of claims 1 to 4. force of 1 ton. The disk-shaped pellets thus obtained were then provided with silver electrodes respectively on both sides thereof. The resulting assemblies 1. Lithiumverbindung, gebildet durch Raktion were used in AC-impedance measurements in an von Lithiumhalogenid und Lithiumimid, wobei electric furnace provided with temperature con- die Reaktion durch Erwärmung eines Gemisches trol means, to determine the temperature depen- dieses Komponenten bei einer Temperatur von dence of the lithium ionic conductivity of each of mindestens 300°C in einer Inertgas- oder the compounds 1 to @. Wasserstoffatmosphäre erfolgt, wobei die Ver- The measurements were carried out under the bindung eine Zusammensetzung der generellen conditions of a frequency 1 KHz, a loaded voltage Formel of 100 mV rms and an atmosphere of nitrogen. Figure 4 shows the temperature dependence of ionic conductivity of the compounds 1 to @ which had been sintered at 300 to 500°C for 10 aufweist, wobei X Chlor, Brom oder Jod ist und y min. den Molanteil von Lithiumimid bedeutet und im In Figure 4, the lines 1 to 6 indicate the Bereich von etwa 0,35 bis etwa 0,98 liegt, wenn X Arrhenius plots for the ionic conductivity of the Chlor ist, im Bereich von 0,25 bis etwa 0,55, wenn compounds 1 to @, respectively. X Brom ist, und im Bereich von etwa 0,33 bis etwa 0,75, wenn X Jod ist. As is clear from 4, the Figure among com- 2. Lithiumverbindung nach Anspruch 1, wobei pounds to this invention, the according com- X in der generellen Formel CI ist. @ and have ionic conductivities of pounds @ high 3. Lithiumverbindung nach Anspruch 1, wobei 1.0x10-1 Sm-1 and 6.0x1-3 Sm-1, respectively, X in der generellen Formel Br ist. and in of they are superior respect temperature 4. Lithiumverbindung nach 1, wobei of ionic Anspruch dependence conductivity. X in der generellen Formel J ist. Accordingly, the compounds of this among 5. Verwendung einer nach invention, those containing iodine as halogen X in Lithiumverbindung einem der Ansprüche 1 bis 4 als ionenleitender the general formula are particularly suitable for fester Elektrolyte. various applications such as room-temperature types of solid state battery, electrochromic dis- 6. Zelle mit einem lithiumionenleitenden festen play, voltameter, capacitor, alkaline ion selective Elektrolyt und an dessen beiden Seiten jeweils film and coulometer. vorgesehenen Elektroden, wobei der feste Elek- trolyt aus einer Lithiumverbindung nach einem der Ansprüche 1 bis 4 besteht.

1. A lithium compound formed by reaction of a lithium halide and lithium imide effected by heating a mixture thereof at a temperature of at 1. Composés de lithium formés par réaction least 300°C in an inert gas or hydrogen atmos- d'un halogénure de lithium et d'une imide de phere, the compound having a composition lithium, mise en oeuvre par chauffage d'un represented by the general formula mélange de ces éléments à une température d'au moins 300°C dans une atmosphère formée d'un gaz inerte ou d'hydrogène, le composé possédant la composition représentée par la formule where X is chlorine, bromine or iodine, and y générale being the molar fraction of lithium imide is in the range of about 0.35 to about 0.98 when X is dans laquelle X est du chlore, du brome ou de 4. Composé de lithium selon la revendication 1, l'iode, et y, qui est la fraction molaire de l'imide de dans lequel X de ladite formule générale est du I. lithium, se situe dans la gamme comprise entre 5. Utilisation d'un composé de lithium con- environ 0,35 et environ 0,98 lorsque X est du formément à l'une quelconque des reven- chlore, entre environ 0,25 et environ 0,55 lorsque dications 1 à 4 entant qu'électrolyte solide four- X est du brome, et entre environ 0,33 et environ nissant une conduction ionique. 0,75 lorsque X est de l'iode. 6. Pile comportant un électrolyte solide pré- 2. Composé de lithium selon la revendication 1, sentant une conduction pour les ions de lithium, dans lequel X de ladite formule générale est du CI. et qui est munie d'électrodes prévues respec- 3. Composé de lithium selon la revendication 1, tivement sur ses deux faces, ledit électrolyte dans lequel X de ladite formule générale est du solide étant constitué par un composé de lithium Br. conformément à l'une des revendications 1 à 4.