A solid electrolyte material is made of Li, Ca, Y, Gd, X, O, and H, where X is at least one selected from the group consisting of F, Cl, Br, and I; and the molar ratio of O to the sum of Y and Gd is greater than 0 and less than 0.82.

The solid electrolyte material of the present disclosure is a solid electrolyte material made of Li, Ca, Y, Gd, X, and O, where X is at least one selected from the group consisting of F, Cl, Br, and I; the molar ratio of O to the sum of Y and Gd in the entire solid electrolyte material is greater than 0 and 0.42 or less; and O is present in a surface region of the solid electrolyte material.

The production method of the present disclosure includes heat-treating a material mixture containing a compound containing Y, a compound containing Sm, NH.sub.4α, Liβ, and Caγ.sub.2 in an inert gas atmosphere. The compound containing Y is at least one selected from the group consisting of Y.sub.2O.sub.3 and Yδ.sub.3, and the compound containing Sm is at least one selected from the group consisting of Sm.sub.2O.sub.3 and Smε.sub.3. The material mixture contains at least one selected from the group consisting of Y.sub.2O.sub.3 and Sm.sub.2O.sub.3, and α, β, γ, δ, and ε are each independently at least one selected from the group consisting of F, Cl, Br, and I.

A positive-electrode material according to the present disclosure includes a positive-electrode active material and a cover layer 111 containing a first solid electrolyte and covering at least partially the surface of the positive-electrode active material. The positive-electrode active material and the cover layer constitute a covered active material; the positive-electrode active material has a pore volume V.sub.α, the covered active material has a pore volume V.sub.β, the positive-electrode active material has a specific surface area Sa, the covered active material has a specific surface area Sp, and at least one selected from the group consisting of 0.20<V.sub.β/V.sub.α<0.88 and 0.81<S.sub.β/S.sub.α<0.97 is satisfied.

A solid state battery is described, which has a negative electrode having a negative electrode active material layer including silicon (Si) as a negative electrode active material. The Si may be present as particles, e.g., microparticles, having an average particle size (D50) of 0.1 μm to 10 μm. The negative electrode active material layer may include the silicon (Si) in an amount of 75 wt % or more, 95 wt % or more, 99 wt % or more, or 99.9 wt % or more, based on 100 wt % of the negative electrode active material layer. The negative electrode active material layer can be free or substantially free of conductive material, carbon, solid state electrolyte, and/or binder. Preferably, after charge/discharge cycles, the negative electrode active material layer forms densified and interconnected large particles of Li—Si alloy, e.g., the Li—Si alloy may have at least one columnar structure and at least one void.

A sulfide solid electrolyte for an all-solid secondary battery includes lithium, phosphorus, sulfur, oxygen, and halogen atoms, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure, the halogen atoms includes chlorine and at least two of bromine, iodine, and fluorine, an atomic ratio of sulfur to oxygen in the sulfide solid electrolyte is about 4 or higher, and an atomic ratio of chlorine to the at least two of bromine, iodine, and fluorine is about 9 or higher.

A sulfide solid electrolyte, which is able to adjust the morphology unavailable traditionally, or is readily adjusted so as to have a desired morphology, the sulfide solid electrolyte having a volume-based average particle diameter measured by laser diffraction particle size distribution measurement of 3 μm or more and a specific surface area measured by the BET method of 20 m.sup.2/g or more; and a method of treating a sulfide solid electrolyte including the sulfide solid electrolyte being subjected to at least one mechanical treatment selected from disintegration and granulation.

There is provided a solid electrolyte production method which can provide a solid electrolyte having a high ion conductivity at low cost with high productivity using a liquid-phase method. The method comprises drying a slurry by fluidized drying using media particles as a medium. The slurry includes a solid electrolyte comprising at least an alkali metal, sulfur atoms and phosphorus atoms as constituent atoms, or a precursor of the solid electrolyte, and a polar solvent.

Provided is a sulfide-based solid electrolyte which is capable of suppressing the generation of hydrogen sulfide caused by reaction with moisture even when in contact with dry air in a dry room or the like, and capable of maintaining lithium ion conductivity. Proposed is a sulfide-based solid electrolyte for a lithium secondary battery, wherein the surface of a compound containing lithium, phosphorus, sulfur, and halogen, and having a cubic argyrodite-type crystal structure is coated with a compound containing lithium, phosphorus, and sulfur, and having a non-argyrodite-type crystal structure.

A production method for producing a halide, the method includes a heat treatment step of heat-treating a mixed material containing (NH.sub.4).sub.aYα.sub.3+a, (NH.sub.4).sub.bGdβ.sub.3+b, Liγ, and Caδ.sub.2 in an inert gas atmosphere, wherein α, β, γ, and δ are each independently at least one selected from the group consisting of F, Cl, Br, and I, and the formulas: 0≤a≤3, 0≤b≤3, and 0<a+b≤6, are satisfied.