Solid electrolyte
Provided is a sulfide-based solid electrolyte comprising lithium, phosphorus, sulfur, and a halogen, as a novel solid electrolyte capable of suppressing generation of hydrogen sulfide and securing ionic conductivity. The solid electrolyte is characterized by comprising Li 7−a PS 6−a Ha a (wherein Ha represents a halogen, and “a” satisfies 0.2<a≤1.8) having an argyrodite-type crystal structure, and Li 3 PS 4 , wherein, in an X-ray diffraction (XRD) pattern obtained through measurement by an X-ray diffraction method, the ratio of the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=26.0° to 28.8° derived from Li 3 PS 4 , relative to the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=24.9° to 26.3° derived from the argyrodite-type crystal structure, is 0.04 to 0.3.
1. A solid electrolyte comprising Li 7−a PS 6−a Ha a , wherein Ha represents a halogen, and “a” satisfies 1.0<a≤1.8, having an argyrodite-type crystal structure, and Li 3 PS 4 ,
wherein, in an X-ray diffraction (XRD) pattern obtained through measurement by an X-ray diffraction method, the ratio of the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=26.0° to 28.8° derived from Li 3 PS 4 , relative to the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=24.9° to 26.3° derived from the argyrodite-type crystal structure, is 0.04 to 0.3.
2. The solid electrolyte according to claim 1 , comprising a compound represented by a compositional formula: Li 7−x−y PS 6−x Ha x−y , wherein Ha represents a halogen, and is Cl or Br, or a combination of both; when Ha is Cl alone, “x” satisfies 0.65<x≤1.8, and “y” satisfies −x/3+2/3<y<−x/3+1.87 and y<x−0.2; and when Ha is Br alone or a combination of Cl and Br, “x” satisfies 0.2<x≤1.8, and “y” satisfies 0<y<−x/3+1.87 and y<x−0.2.
3. A lithium secondary battery comprising the solid electrolyte according to claim 1 .
4. A lithium secondary battery comprising the solid electrolyte according to claim 1 and a negative electrode active material containing carbon or silicon.
5. A lithium secondary battery comprising the solid electrolyte according to claim 1 and a positive electrode active material containing lithium.
6. The solid electrolyte according to claim 1 , wherein, in an X-ray diffraction (XRD) pattern obtained through measurement by an X-ray diffraction method, the ratio of the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=26.0° to 28.8° derived from Li 3 PS 4 , relative to the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=24.9° to 26.3° derived from the argyrodite-type crystal structure, is 0.04 to 0.2.
7. The solid electrolyte according to claim 1 , wherein, in an X-ray diffraction (XRD) pattern obtained through measurement by an X-ray diffraction method, the ratio of the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=26.0° to 28.8° derived from Li 3 PS 4 , relative to the peak intensity of a peak appearing at a position in a range of diffraction angle 2θ=24.9° to 26.3° derived from the argyrodite-type crystal structure, is 0.04 to 0.1.
8. The solid electrolyte according to claim 1 , comprising a compound represented by a compositional formula: Li 7−x−y PS 6−x Ha x−y , wherein Ha represents a halogen, and is Br, or a combination of both Cl and Br, and when Ha is Br alone or a combination of Cl and Br, “x” satisfies 0.2<x≤1.8, and “y” satisfies 0<y<−x/3+1.87 and y<x−0.2.
9. The solid electrolyte according to claim 1 , wherein a D50 in a volume-based particle size distribution obtained via measurement by a laser diffraction scattering-type particle size distribution measurement method is 0.1 to 10 μm.
10. The solid electrolyte according to claim 1 , wherein two or three of α-Li 3 PS 4 , β-Li 3 PS 4 , and γ-Li 3 PS 4 are contained.