Patent Application
20100290969
The present invention relates to a novel class of lithium-rich solid-state compounds, a process for their preparation and their use as solid electrolytes in primary and secondary electrochemical energy stores.
Argyrodites have long been known and are derived from argyrodite Ag8GeS6, which was described for the first time in 1886 by C. Winkler and the analysis of which led to the discovery of germanium. The argyrodite family consists of more than 100 crystalline solids and includes, for example, those solid-state compounds in which the silver is replaced by copper, the germanium by gallium or phosphorus and the sulfur by selenium. Thus, Nitsche, Kuhs, Krebs, Evain, Boucher, Pfitzner and Nilges describe, inter alia, compounds such as Cu9GaS6, Ag7PSe6 and Cu8GaS5Cl, the solid-state structures of which are derived from argyrodite.
Li argyrodites were unknown for a long time, with the exception of the insufficiently characterized compound Li7PS6 (J. F. Brice, C. R. Seances in Acad. Sci. 1976, C283, 581). Recent investigations, for example by Eckert, Zhang and Kennedy in Chem. of Mat. 1990, 2, 273-279, relate to thermomechanical optimization experiments for the Li2S—P2S5 system and show as a whole samples which do not have a single phase. However, signs of high lithium mobility are found for this system in many samples.
More detailed investigations have, however, shown that the production of single-phase solids in the Li2S—P2S5 system is difficult and is greatly dependent, inter alia, on the starting materials and crucible materials used during the preparation, so that different byproducts form depending on the material used.
It is therefore an object of the present invention to provide a novel class of lithium-rich solid-state compounds which permit single-phase preparation in addition to high lithium ion mobility.
This object is achieved, according to the invention, by lithium argyrodites of the general formula (I):
Li+(12-n-x)Bn+X2−6-xY−x (I)
in which
Bn+ is selected from the group consisting of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb and Ta,
X2− is selected from the group consisting of S, Se and Te,
Y− is selected from the group consisting of Cl, Br, I, F, CN, OCN, SCN, N3, and in which 0≦x≦2.
Advantageously, the inventive class of novel lithium-rich argyrodites permits preparation of single-phase solids. In addition, the inventive compounds of the novel class have high lithium ion mobility, which can preferably be employed in a use as solid electrolyte. In contrast to known lithium electrolytes, the lithium argyrodites according to the invention can be used in a wide temperature range from −150° C. to 600° C. Thus, the temperature sensitivity of electrochemical energy stores which has been observable to date can be reduced.
The component Bn+ can preferably be selected from the group consisting of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb and Ta. P, As, Sb and Ga are particularly preferred, especially with regard to use as an electrolyte constituent of a lithium accumulator.
The component X2− can be selected from the group consisting of S, Se and Te. In particular, components X2− selected from the group consisting of S and Se are favored in a preferred configuration of the invention, owing to their easier preparation.
The component Y− can preferably be selected from the group consisting of Cl, Br, I, F, OCN, SCN, N3, CN. Cl, Br and I are particularly preferred, especially with regard to use as an electrolyte constituent of a lithium accumulator.
The lithium argyrodites according to the invention can preferably be compounds of the general formula (II):
Li6PS5Z (II),
in which the constituent Z may be a monovalent anion selected from the group consisting of the halides and the pseudohalides.
In a further preferred embodiment of the present invention, the component Z can be selected from the group consisting of Cl, Br, I.
Particularly when Z═I, these compounds show a high specific Li+ ion conductivity, in said case Z═I of about 7×103 Scm−1 at room temperature. NMR investigations on these compounds have also indicated a high specific Li+ mobility.
The compounds of the formula (II) where Z═Cl, Br or I can advantageously be prepared in a solid-state synthesis, for example according to the following reactions:
6 Li2S+2 P+½ S8+I2→2 Li6PS5I
5 Li2S+2 P+⅝ S8+2 LiBr→2 Li6PS5Br
5 Li2S+2 P+⅝ S8+2 LiCl→2 Li6PS5Cl
In a further preferred embodiment of the invention, the lithium argyrodites can be compounds of the general formula (III):
Li6B6+S5-aX2−aY− (III)
in which
B6+ is selected from the group consisting of P, As and Sb,
X2− is selected from the group consisting of Se and Te,
Y− is selected from the group consisting of Cl, Br, I, F, CN, OCN, SCN, N3, and in which 0≦a≦2.
Furthermore preferred are inventive lithium argyrodites of the general formula (IV):
Li7B6+S6-aX2−a (IV)
in which
B6+ is selected from the group consisting of P, As and Sb,
X2− is selected from the group consisting of Se and Te, and in which 0≦a≦2.
The invention moreover relates to a process for the preparation of lithium argyrodites of the general formula (I), characterized by the steps:
According to the invention, a process which permits a simple procedure in addition to a good single-phase character of the crystalline compounds can advantageously be provided.
The process according to the invention can be carried out in particular at a temperature of from 500° C. to 600° C., preferably at 550° C.
In a further advantageous embodiment of the process, a duration of from 4 days to 8 days, preferably a duration of 7 days, can be provided.
An inventive lithium argyrodite of the general formula (I) can preferably be used as a lithium ion electrolyte for primary and secondary electrochemical energy stores.
The invention is described further by the following examples without being limited thereto.
For the preparation of the compound Li6PS5I, the starting materials I2, S8, Li2S and P2S5 were weighed out in the stoichiometric ratio under an argon inert gas atmosphere, transferred to a graphitized quartz ampoule and melted in vacuo. The sample was heated in a tubular furnace at a temperature of 550° C. for 6 days and then slowly cooled. Single-phase crystals of the compound Li6PS5I were obtained as a white solid.
For the preparation of the compound Li6PS5Br, the starting materials LiBr, Li2S and P2S5 were weighed out in the stoichiometric ratio under an argon inert gas atmosphere, transferred to a graphitized quartz ampoule and melted in vacuo. The sample was heated in a tubular furnace at a temperature of 550° C. for 6 days and then slowly cooled. Single-phase crystals of the compound Li6PS5Br were obtained as a white solid.
For the preparation of the compound Li6PS5Cl, the starting materials LiCl, Li2S and P2S5 were weighed out in the stoichiometric ratio under an argon inert gas atmosphere, transferred to a graphitized quartz ampoule and melted in vacuo. The sample was heated in a tubular furnace at a temperature of 550° C. for 6 days and then slowly cooled. Single-phase crystals of the compound Li6PS5Cl were obtained as a white solid.
For the preparation of the compound Li7PS5Se, the starting materials S8, Li2S and P2Se5 were weighed out in the stoichiometric ratio under an argon inert gas atmosphere, transferred to a graphitized quartz ampoule and melted in vacuo. The sample was heated in a tubular furnace at a temperature of 500° C.-550° C. for 6 days and then slowly cooled. Single-phase crystals of the compound Li7PS5Se were obtained as a white solid.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 048 289.4 | Oct 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/063412 | 10/7/2008 | WO | 00 | 6/28/2010 |
