LITHIUM ION CONDUCTING SOLID MATERIALS

Abstract

Described are a solid material which has ionic conductivity for lithium ions, a process for preparing said solid material, a use of said solid material as a solid electrolyte for an electrochemical cell, a solid structure selected from the group consisting of a cathode, an anode and a separator for an electrochemical cell comprising the solid material, and an electrochemical cell comprising such solid structure.

Claims

1. A solid material having a composition according to general formula (I) Li.sub.7+x−yM.sub.xSb.sub.1−xS.sub.6−yX.sub.y wherein M is one or more selected from the group consisting of Si, Ge and Sn; 0≤x<1; X is one or more selected from the group consisting of Cl, Br and I; 0.05≤y<2.

2. The solid material according to claim 1, wherein 0.05≤x<1 and/or 0.5≤y<1.5.

3. The solid material according to claim 2, wherein M is Si; 0.1<x<0.8; 0.5<y<1.5.

4. The solid material according to claim 2, wherein M is Ge; 0.1<x<0.5; 0.5<y<1.5.

5. The solid material according to claim 2, wherein M is Sn; 0.1<x<0.3; 0.5<y<1.5.

6. The solid material according to claim 1, wherein X is I.

7. The solid material according to claim 1, wherein the solid material comprises a crystalline phase having the argyrodite structure.

8. A process for preparing a solid material as defined in claim 1, comprising a) preparing or providing a reaction mixture comprising the precursors (1) Li.sub.2S (2) one or both of Sb.sub.2S.sub.3 and elemental Sb (3) one or more compounds LiX wherein X is selected from the group consisting of Cl, Br and I (4) elemental S (5) optionally one or more species selected from the group consisting of M in elemental form and sulfides of M, wherein in each case M is selected from the group consisting of Si, Ge and Sn wherein in the reaction mixture the molar ratio of the elements Li, M, Sb, S and X matches general formula (I) b) heat-treating the reaction mixture in a temperature range of from 400° C. to 600° C. for a total duration of 40 hours to 200 to obtain a reaction product c) cooling the reaction product obtained in step b) so that a solid material having a composition according to general formula (I) is obtained.

9. The process according to claim 8, further comprising d) annealing the solid material obtained in step c) in a temperature range of from 400° C. to 600° C. for a duration of 40 hours to 200 hours.

10. The process according to claim 8, wherein the precursors are (1) Li.sub.2S, (2) Sb.sub.2S.sub.3, (3) LiI, (4) S and (5) one of elemental Si, elemental Ge, elemental Sn, SiS.sub.2, GeS.sub.2 and SnS.sub.2.

11. A solid electrolyte for an electrochemical cell comprising the solid material according to claim 1, wherein preferably the solid electrolyte is a component of a solid structure for an electrochemical cell selected from the group consisting of cathode, anode and separator.

12. A solid structure for an electrochemical cell, wherein the solid structure is selected from the group consisting of cathode, anode and separator, wherein the solid structure for an electrochemical cell comprises a solid material according to claim 1.

13. An electrochemical cell comprising a solid material according to claim 1.

14. The electrochemical cell according to claim 13, wherein the solid material is a component of a solid structure, and wherein the solid structure is selected from the group consisting of cathode, anode and separator.

Description

[0191] For the evaluation of the stability of the solid electrolyte Li.sub.6.7Si.sub.0.7Sb.sub.0.3S.sub.5I, the solid state LilLi.sub.6.7Si.sub.0.7Sb.sub.0.3S.sub.5IlLi symmetric cell was cycled at different current and capacity (0.3 mA/cm.sup.2 and 0.3 mAh/cm.sup.2 for 600 h; and then 0.6 mA/cm.sup.2, 0.6 mAh/cm.sup.2 for another 430 hours). As evident from FIG. 1, a substantially steady voltage profile was obtained. This indicates electrochemical stability of the studied solid electrolyte in direct contact with lithium metal over a duration of at least about 1,000 hours under conditions of stripping and plating in a symmetric cell as described above.

[0192] 4. Structure Analysis

[0193] Powder X-ray diffraction (XRD) measurements were conducted at room temperature using a PANalytical Empyrean diffractometer with Cu-Kα radiation equipped with a PIXcel bidimensional detector. XRD patterns for phase identification were obtained in Debye-Scherrer geometry, with samples sealed in sealed in 0.3 mm glass capillaries under argon.

[0194] XRD patterns of several solid materials having a composition according to formula (I) with M=Si, Ge or Sn, resp., are shown in FIGS. 2a and 2b. In each case, the cubic space group F-43m was indexed that is adopted by most other argyrodites.

[0195] The XRD patterns in FIG. 2a show that the solid materials having a composition according to formula (I) with M=Si are polycrystalline powders, and very minor fractions of Lil and Li.sub.2S are present beside the material having a composition according to formula (I). Increasing the amount of Si (parameter x) results in an increasing fraction of said secondary phases (mainly originating from the precursors Lil and Li.sub.2S).

[0196] In the XRD patterns of the solid materials with M=Si, the argyrodite peaks shift to smaller d-spacing (smaller distance between the crystal planes) with increasing Si.sup.4+content (see enlarged part of FIG. 2a). This indicates successful substitution of Sb.sup.5+with the smaller Si.sup.4+ion.

[0197] The XRD patterns in FIG. 2b show that the materials having a composition according to formula (I) with M=Ge are phase-pure polycrystalline powders and the material having a composition according to formula (I) with M=Sn is accompanied by trace amounts of unknown impurity and Lil in the XRD pattern.