Sulfide-based solid electrolyte, all-solid secondary battery including the same, and method of preparing the sulfide-based solid electrolyte
A sulfide solid electrolyte includes: an ionic conductor including a PS 4 3− unit, a P 2 S 6 4− unit, and a P 2 S 7 4− unit; and a lithium compound containing a halogen element, wherein a molar ratio of the P 2 S 6 4− unit to the PS 4 3− unit is about 1:1 to about 5:1, and a molar amount of the P 2 S 7 4− unit with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit is greater than 0 to about 60%.
1. A sulfide solid electrolyte comprising:
an ionic conductor comprising a PS 4 3− unit, a P 2 S 6 4− unit, and a P 2 S 7 4− unit; and
a lithium compound comprising a LiCl,
wherein
a molar ratio of the P 2 S 6 4− unit to the PS 4 3− unit is 1:1 to 5:1,
a molar amount of the P 2 S 7 4− unit is greater than 0 to 60% or less, with respect to a total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit,
a molar amount of the PS 4 3− unit is 5% to 30%, with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit, and
wherein the sulfide solid electrolyte is amorphous and has an ionic conductivity at room temperature of 1×10 −3 Siemens per centimeter to 1×10 −1 Siemens per centimeter.
2. The sulfide-based solid electrolyte of claim 1 , wherein
the molar ratio of the P 2 S 6 4− unit to the PS 4 3− unit is 2:1 to 5:1, and
the molar amount of the P 2 S 7 4− unit with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit is greater than 0 to 40%.
3. The sulfide solid electrolyte of claim 1 , wherein, with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit, the proportion of the P 2 S 6 4− unit is 40% to 80%, and the proportion of the P 2 S 7 4− unit is greater than the proportion of the PS 4 3− unit.
4. The sulfide solid electrolyte of claim 1 , wherein the ionic conductor comprises Li 3 PS 4 , Li 4 P 2 S 6 , and Li 7 P 3 S 11 .
5. The sulfide solid electrolyte of claim 4 , further comprising a crystalline phase comprising at least one of Li 3 PS 4 , Li 4 P 2 S 6 , or Li 7 P 3 S 11 .
6. The sulfide solid electrolyte of claim 4 , wherein, in an X-ray diffraction spectrum of the ionic conductor,
a first peak corresponding to Li 7 P 3 S 11 appears at a diffraction angle of 29.8°±0.5° 2θ, and
a second peak corresponding to Li 4 P 2 S 6 appears at a diffraction angle of 32.5°±0.5° 2θ.
7. The sulfide solid electrolyte of claim 1 , wherein the lithium compound further comprises LiI, LiF, LiBr, or a combination thereof.
8. The sulfide solid electrolyte of claim 1 , wherein the amount of the lithium compound is about 3 weight percent to about 22 weight percent, with respect to the total weight of the sulfide solid electrolyte.
9. The sulfide solid electrolyte of claim 1 , wherein the sulfide solid electrolyte is a reaction product of a starting material composition comprising the elements P, S, and Li, and
the lithium compound containing the halogen element.
10. The sulfide solid electrolyte of claim 9 , wherein the starting material composition comprises Li 2 S and P 2 S 5 .
11. The sulfide solid electrolyte of claim 9 , wherein the starting material composition comprises Li 2 S and P 2 S 5 in a molar ratio of about 1:1 to about 9:1.
12. The sulfide solid electrolyte of claim 9 , wherein an amount of the lithium compound is about 3 weight percent to about 22 weight percent, with respect to the total weight of the starting material composition and the lithium compound.
13. The sulfide solid electrolyte of claim 1 , wherein the sulfide solid electrolyte has an elastic modulus which is less than an elastic modulus of a crystalline argyrodite-type solid electrolyte having a same composition.
14. An all-solid secondary battery comprising:
a cathode layer;
an anode layer; and
a solid electrolyte layer disposed between the cathode layer and the anode layer,
wherein the solid electrolyte layer comprises the sulfide solid electrolyte according to claim 1 .
15. The all-solid secondary battery of claim 14 , wherein the all-solid secondary battery has a charge-discharge efficiency of about 50% or greater at a first cycle.
16. A method of preparing a sulfide solid electrolyte, the method comprising:
providing a mixture comprising
a starting material composition comprising elements P, S, and Li, and
a lithium compound comprising a LiCl; and
treating the mixture to prepare the sulfide solid electrolyte,
wherein the sulfide solid electrolyte comprises
an ionic conductor comprising a PS 4 3− unit, a P 2 S 6 4− unit, and a P 2 S 7 4− unit, and
the lithium compound containing a LiCl,
wherein a molar ratio of the P 2 S 6 4− unit to the PS 4 3− unit is 1:1 to 5:1,
wherein a molar amount of the P 2 S 7 4− unit is greater than 0 to 60%, with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit,
a molar amount of the PS 4 3− unit is 5% to 30%, with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit, and
wherein the sulfide solid electrolyte is amorphous and has an ionic conductivity at room temperature of 1×10 −3 Siemens per centimeter to 1×10 −1 Siemens per centimeter.
17. The method of claim 16 , wherein the mixture is prepared by mixing the starting material composition and the lithium compound.
18. The method of claim 16 , wherein the treating of the mixture comprises:
contacting the mixture to prepare a solid electrolyte precursor; and
thermally treating the solid electrolyte precursor at a temperature of about 150° C. to about 350° C. to prepare the sulfide solid electrolyte.
19. A sulfide solid electrolyte, comprising:
an ionic conductor comprising a PS 4 3− unit, a P 2 S 6 4− unit, and a P 2 S 7 4− unit; and
a lithium compound comprising a LiCl, wherein an amount of the lithium compound is about 3 weight percent to about 22 weight percent with respect to the total weight of the sulfide solid electrolyte,
wherein a molar ratio of the P 2 S 6 4− unit to the PS 4 3− unit is 1:1 to 5:1,
a molar amount of the P 2 S 7 4− unit is greater than 0 to 60%, with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit,
a molar amount of the PS 4 3− unit is 5% to 30%, with respect to the total molar amount of the PS 4 3− unit, the P 2 S 6 4− unit, and the P 2 S 7 4− unit, and
wherein the sulfide solid electrolyte is amorphous and has an ionic conductivity at room temperature of 1×10 −3 Siemens per centimeter to 1×10 −1 Siemens per centimeter, and
wherein the sulfide solid electrolyte is a reaction product of a starting material composition comprising the elements P, S, and Li, and the lithium compound containing the halogen element.
20. The sulfide solid electrolyte of claim 13 , wherein the sulfide solid electrolyte has an elastic modulus of about 10 gigapascals to about 30 gigapascals.