The present disclosure provides a solid electrolyte material having a high lithium ion conductivity. The solid electrolyte material according to the present disclosure consists essentially of Li, Zr, Y, M, and X. M is at least one element selected from the group consisting of Al, Ga, In, Sc, and Bi. X is at least one element selected from the group consisting of Cl and Br.

An ion conductor exhibiting high lithium ion conductivity in the form of a molded product without firing is provided. The ion conductor contains an ion conductive powder having lithium ion conductivity and an ionic liquid having lithium ion conductivity. The ionic liquid has an average thickness of 5 nm or more.

To provide a polymer electrolyte membrane which can be applied to a polymer electrolyte water electrolyzer, and is capable of producing a polymer electrolyte water electrolyzer having a low electrolytic voltage and excellent in hydrogen gas recovery efficiency, as well as a membrane electrode assembly and a polymer electrolyte water electrolyzer obtainable by using it.

The polymer electrolyte membrane of the present invention contains a polymer electrolyte, of which the hydrogen gas permeation coefficient under the conditions of a temperature of 80° C. and a relative humidity of 10%, is at most 2.4 x 10.sup.−9 cm.sup.3.cm/(s.cm.sup.2.cmHg), wherein the membrane resistance value under the conditions of a temperature of 80° C. and a relative humidity of 50%, is from 50 to 150 mn.cm2.

As a novel sulfide compound having a low elastic modulus while retaining the high ion conductivity, a sulfide compound for a solid electrolyte of a lithium secondary battery that includes a crystal phase of a cubic argyrodite type crystal structure, and is represented by the compositional formula: Li.sub.7−xPS.sub.6−xCl.sub.yBr.sub.z, wherein x in the compositional formula satisfies x=y+z and 1.0<x≤1.8, and a ratio (z/y) of the molar ratio of Br to the molar ratio of Cl is from 0.1 to 10.0 is proposed.

A solid electrolyte material includes Li, Ca, Y, Gd, and X wherein X is at least one element selected from the group consisting of F, Cl, Br, and I. A battery uses the solid electrolyte material.

The solid electrolyte material of the present disclosure includes Li, M, O, X, and F. M is at least one element selected from the group consisting of Ta and Nb. X is at least one element selected from the group consisting of Cl, Br, and I.

A mixed ionic-electronic conductor (MIEC) in contact with a solid electrolyte includes a material having a bandgap less than 3 eV. The material includes an end-member phase directly connected to an alkali metal by a tie-line in an equilibrium phase diagram. The material is thermodynamically stable with a solid electrolyte. The MIEC includes plurality of open pores, formed within the MIEC, to facilitate motion of the alkali metal to at least one of store the alkali metal in the plurality of open pores or release the alkali metal from the plurality of open pores. The solid electrolyte has an ionic conductivity to ions of the alkali metal greater than 1 mS cm.sup.−1, a thickness less than 100 μm, and comprises at least one of a ceramic or a polymer.

A mixed ionic-electronic conductor (MIEC) in contact with a solid electrolyte includes a material having a bandgap less than 3 eV. The material includes an end-member phase directly connected to an alkali metal by a tie-line in an equilibrium phase diagram. The material is thermodynamically stable with a solid electrolyte. The MIEC includes plurality of open pores, formed within the MIEC, to facilitate motion of the alkali metal to at least one of store the alkali metal in the plurality of open pores or release the alkali metal from the plurality of open pores. The solid electrolyte has an ionic conductivity to ions of the alkali metal greater than 1 mS cm.sup.−1, a thickness less than 100 μm, and comprises at least one of a ceramic or a polymer.

An electrochemical device has a laminated body including: a positive electrode; a negative electrode; and a solid electrolyte sandwiched between the positive electrode and the negative electrode, wherein the laminated body contains water, a content of the water contained in the laminated body is 0.001 mass % or more and less than 0.3 mass % with respect to the laminated body, a part of the water is a bound water bonding with a constituent of the laminated body, and a ratio of the bound water in the water is 50% or more and 90% or less.

An oriented apatite-type oxide ion conductor includes a composite oxide expressed as A.sub.9.33+x[T.sub.6.00−yM.sub.y]O.sub.26.0+z, where A represents one or two or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba, T represents an element including Si or Ge or both, and M represents one or two or more elements selected from the group consisting of B, Ge, Zn, Sn, W, and Mo, and where x is from −1.00 to 1.00, y is from 0.40 to less than 1.00, and z is from −3.00 to 2.00.