Solid electrolyte including nitrogen and sulfur, electrochemical cell including solid electrolyte, and method of preparing sold electrolyte

An all-solid-state secondary battery comprising:

• a cathode layer;
• an anode layer;
• and
• a solid electrolyte layer disposed between the cathode layer and the anode layer,
• wherein, at least one of the solid electrolyte layer or the cathode layer comprises a solid electrolyte, and the solid electrolyte comprises a compound represented by Formula 1-1,
• wherein, in Formula 1-1,
• M is at least one of Na, K, Ca, Fe, Mg, Ag, Cu, Zr, or Zn,
• X is at least one of Cl, Br, F, I, or a pseudohalogen, and
• 0.1≤x≤0.125, 0<a<1, and 0<d≤1, and
• the compound of Formula 1-1 has an argyrodite crystal structure.