An all-solid state secondary battery including: a positive electrode active material layer; a solid electrolyte layer; and a negative electrode active material layer in this order. At least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is a layer including an inorganic solid electrolyte having conductivity for ions of metal elements belonging to Group I or II of the periodic table and binder particles which have an average particle diameter of 10 nm or more and 50,000 nm or less and encompass an ion-conductive substance. The binder particles are formed of the ion-conductive substance and a polymer, and the ion-conductive substance is coated with the polymer having a mass ratio of 30% or more and 100% or less of the ion-conductive substance.

Methods for wet chemical synthesis of lithium argyrodites are provided, which in some embodiments include includes dissolving a stoichiometric mixture of precursors in a small quantity of solvent in an argon atmosphere, drying the mixture under vacuum or an inert gas atmosphere to evaporate the solvent, and then annealing to obtain a final lithium argyrodite product. Further embodiments comprise synthesizing the precursors, and excess halide doping to achieve higher ionic conductivity.

The present disclosure provides a solid electrolyte material having high lithium ion conductivity. The solid electrolyte material of the present disclosure includes Li, M and X. M is at least one element selected from the group consisting of Mg, Zn and Cd. X is at least two elements selected from the group consisting of Cl, Br and I.

A solid electrolyte contains a thio-LISICON Region II-type crystal structure, where the solid electrolyte does not contain P.sub.2S.sub.6.sup.4− structure. A solid electrolyte, where:

(1) a signal of a thio-LISICON Region II-type crystal structure is observed in the solid .sup.31P-NMR spectrometry, and

(2) a signal of a P.sub.2S.sub.6.sup.4− structure is not observed in the solid .sup.31P-NMR spectrometry.

The invention is to provide a novel method for producing a solid electrolyte having a high ionic conductivity according to a liquid-phase method. The production method for a solid electrolyte includes mixing a raw material inclusion containing a lithium atom, a sulfur atom, a phosphorus atom and a halogen atom with a complexing agent and a solvent, wherein the amount of the complexing agent is 0.1 mL or more and 4.0 mL or less relative to 1 g of the total mass of the raw material inclusion.

A solid electrolyte includes a compound having an argyrodite crystal structure represented by Formula 1,

Li.sub.aM.sub.xPS.sub.bBr.sub.cX.sub.d.  Formula 1

wherein Formula 1, M is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof; X is Cl, I, or a combination thereof; and 0≤x<1, 5≤(a+x)<7, 5≤a≤6, 4≤b≤6, 0<(c+d)≤2, and (c/d)>4.

A solid electrolyte includes a compound having an argyrodite crystal structure represented by Formula 1,

Li.sub.aM.sub.xPS.sub.bBr.sub.cX.sub.d.  Formula 1

wherein Formula 1, M is Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof; X is Cl, I, or a combination thereof; and 0≤x<1, 5≤(a+x)<7, 5≤a≤6, 4≤b≤6, 0<(c+d)≤2, and (c/d)>4.

Aspects of the present disclosure involve a plasma system for practicing various methods of synthesizing solid-state electrolyte materials and precursors for solid-state electrolyte materials.

Aspects of the present disclosure involve a plasma system for practicing various methods of synthesizing solid-state electrolyte materials and precursors for solid-state electrolyte materials.

A compound according to an embodiment of the present disclosure is represented by Formula 1. An electrolyte for a lithium secondary battery according to an embodiment of the present disclosure may include the compound, and a lithium secondary battery according to an embodiment of the present disclosure may include the electrolyte.