A solid electrolyte contains a compound that has a crystal phase having an argyrodite-type crystal structure and that is represented by Li.sub.aPS.sub.bX.sub.c, where X is at least one elemental halogen, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less. The proportion of the crystal phase with an argyrodite-type structure relative to all crystal phases constituting the solid electrolyte is 97.0 wt % or more. The compound has a lattice strain of less than 0.10%. The solid electrolyte preferably exhibits a lithium ion conductivity of 4.0 mS/cm or more.

One aspect of the present invention is a solid electrolyte which has a crystal structure attributable to a space group F-43m and contains lithium, phosphorus, sulfur, and an element A, in which the element A is a metal element having an ionic radius of more than 59 pm and 120 pm or less in 4-fold coordination and 6-fold coordination in an ion crystal.

A solid electrolyte: (compound A) a compound that has a crystal phase having an argyrodite-type crystal structure and that is represented by Li.sub.aPS.sub.bX.sub.c, where X is at least one elemental halogen, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less; and (compound B) a compound that is represented by LiX, where X is as defined above. The compound B has a crystallite size of 25 nm or more. The solid electrolyte preferably has a BET specific surface area of 14.0 m.sup.2/g or less.

A sulfide solid electrolyte is provided having peak A at 2θ=20.7°±0.5° in an X-ray diffraction pattern obtained by performing X-ray diffraction measurement using CuKα1 radiation. It is preferable that the sulfide solid electrolyte has peak B at 2θ=25.4°±1.0° in the X-ray diffraction pattern obtained by performing X-ray diffraction measurement using CuKα1 radiation. It is also preferable that the value of the ratio of I.sub.A to I.sub.B, I.sub.A/I.sub.B, is more than 0 and 0.7 or less, where I.sub.A is the intensity of peak A and I.sub.B is the intensity of peak B. It is also preferable that the sulfide solid electrolyte has peak C at 2θ=22.0°±0.5° in the X-ray diffraction pattern obtained by performing X-ray diffraction measurement using CuKα1 radiation.

A solid electrolyte composition containing an inorganic solid electrolyte having conductivity of an ion of a metal belonging to Group I or II of the periodic table and an acid-modified cellulose nanofiber, a solid electrolyte-containing sheet and a manufacturing method therefor, and an all-solid state secondary battery having an inorganic solid electrolyte layer containing the inorganic solid electrolyte having conductivity of an ion of a metal belonging to Group I or II of the periodic table and an acid-modified cellulose nanofiber and a manufacturing method therefor.

Provided is a phosphorus sulfide composition for a sulfide-based inorganic solid electrolyte material, the phosphorus sulfide composition including P.sub.4S.sub.10 and P.sub.4S.sub.5, in which when a total content of P.sub.4S.sub.10, P.sub.4S.sub.5, P.sub.4S.sub.7, and P.sub.4S.sub.3 in the phosphorus sulfide composition is represented by 100 mass %, a content of P.sub.4S.sub.10 calculated from a solid .sup.31P-NMR spectrum is 70 mass % or more and 99 mass % or less.

A method of manufacturing an inorganic material includes: a step (A) of preparing a first inorganic material as a raw material; and a step (B) of obtaining a second inorganic material by crushing the first inorganic material using a ball mill to obtain fine particles of the first inorganic material, the ball mill including a cylindrical container and crushing balls, in which the step (B) includes a step (B1) of putting the first inorganic material and the crushing balls into the cylindrical container and subsequently rotating the cylindrical container about a cylindrical shaft and a step (B2) of moving the cylindrical container such that the first inorganic material moves in the cylindrical shaft direction.

A method of production of a solid electrolyte having an Argyrodite-type crystal structure, including steps of mixing raw materials such that lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (X) satisfy the following formulas (11) to (14) to obtain a mixture; and heating the mixture:

4.8≤Li/P≤5.3  (11)

3.8≤S/P≤4.4  (12)

0<O/P≤0.8  (13)

1.0<X/P≤2.0  (14) wherein the formula (11) represents a molar ratio of Li to P, the formula (12) represents a molar ratio of S to P, the formula (13) represents a molar ratio of O to P, and the formula (14) represents a molar ratio of halogen (X) to P.

A solid electrolyte includes: (compound A) a compound that has a crystal phase having an argyrodite-type crystal structure and that is represented by Li.sub.aPS.sub.bX.sub.c, where X is at least one elemental halogen, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less; and (compound B) a compound that is represented by LiX, where X is as defined above. The compound B has a crystallite size of 60 nm or less. The solid electrolyte according to the present invention preferably exhibits a lithium ion conductivity at 25° C. of 4.0 mS/cm or more.

An inorganic solid electrolyte-containing composition is an inorganic solid electrolyte-containing composition for an all-solid state secondary battery, containing an inorganic solid electrolyte, a polymer binder, a metal element-containing compound, and a dispersion medium, in which the metal element-containing compound is a compound that is capable of supplying, as an ion, a metal element constituting a molecule to a polymer that forms the polymer binder, and the polymer binder is dissolved in the dispersion medium, where the metal element-containing compound is present in a solid state.