A solid electrolyte material contains Li, M, and X. M contains Y, and X is at least one selected from the group consisting of Cl, Br, and I. A first converted pattern, which is obtained by converting the X-ray diffraction pattern of the solid electrolyte material to change its horizontal axis from the diffraction angle to q, includes its base peak within the range in which q is 2.109 Å.sup.−1 or more and 2.315 Å.sup.−1 or less. A second converted pattern, which is obtained by converting the X-ray diffraction pattern to change its horizontal axis from the diffraction angle to q/q.sub.0, where q.sub.0 is the q corresponding to the base peak in the first converted pattern, includes a peak within each of the range in which q/q.sub.0 is 1.28 or more and 1.30 or less and the range in which q/q.sub.0 is 1.51 or more and 1.54 or less.

A solid electrolyte material contains Li, M, and X. M contains Y, and X is at least one selected from the group consisting of Cl, Br, and I. A first converted pattern, which is obtained by converting the X-ray diffraction pattern of the solid electrolyte material to change its horizontal axis from the diffraction angle to q, includes its base peak within the range in which q is 2.109 Å.sup.−1 or more and 2.315 Å.sup.−1 or less. A second converted pattern, which is obtained by converting the X-ray diffraction pattern to change its horizontal axis from the diffraction angle to q/q.sub.0, where q.sub.0 is the q corresponding to the base peak in the first converted pattern, includes a peak within each of the range in which q/q.sub.0 is 1.28 or more and 1.30 or less and the range in which q/q.sub.0 is 1.51 or more and 1.54 or less.

According to one embodiment, a separator is provided. The separator includes a composite membrane. The composite membrane includes a substrate layer, a first composite layer, and a second composite layer. The first composite layer is located on one surface of the substrate layer. The second composite layer is located on the other surface of the substrate layer. The composite membrane has a coefficient of air permeability of 1×10.sup.−14 m.sup.2 or less. The first composite layer has a first surface and a second surface. The first surface is in contact with the substrate layer. The second surface is located on an opposite side to the first surface. Denseness of a portion including the first surface is lower than denseness of a portion including the second surface in the first composite layer.

According to one embodiment, a separator is provided. The separator includes a composite membrane. The composite membrane includes a substrate layer, a first composite layer, and a second composite layer. The first composite layer is located on one surface of the substrate layer. The second composite layer is located on the other surface of the substrate layer. The composite membrane has a coefficient of air permeability of 1×10.sup.−14 m.sup.2 or less. The first composite layer has a first surface and a second surface. The first surface is in contact with the substrate layer. The second surface is located on an opposite side to the first surface. Denseness of a portion including the first surface is lower than denseness of a portion including the second surface in the first composite layer.

This solid electrolyte is a zirconium phosphate-based solid electrolyte in which a part of phosphorous or zirconium that is contained in the solid electrolyte is substituted with an element with a variable valence.

This solid electrolyte is a zirconium phosphate-based solid electrolyte in which a part of phosphorous or zirconium that is contained in the solid electrolyte is substituted with an element with a variable valence.

Setter plates are fabricated from Li-stuffed garnet materials having the same, or substantially similar, compositions as a garnet Li-stuffed solid electrolyte. The Li-stuffed garnet setter plates, set forth herein, reduce the evaporation of Li during a sintering treatment step and/or reduce the loss of Li caused by diffusion out of the sintering electrolyte. Li-stuffed garnet setter plates, set forth herein, maintain compositional control over the solid electrolyte during sintering when, upon heating, lithium is prone to diffuse out of the solid electrolyte.

Setter plates are fabricated from Li-stuffed garnet materials having the same, or substantially similar, compositions as a garnet Li-stuffed solid electrolyte. The Li-stuffed garnet setter plates, set forth herein, reduce the evaporation of Li during a sintering treatment step and/or reduce the loss of Li caused by diffusion out of the sintering electrolyte. Li-stuffed garnet setter plates, set forth herein, maintain compositional control over the solid electrolyte during sintering when, upon heating, lithium is prone to diffuse out of the solid electrolyte.

A composite containing phosphorus, lithium, iron, sulfur, and carbon as constituent elements wherein lithium sulfide (Li.sub.2S) is present in an amount of 90 mol % or more, and wherein the crystallite size calculated from the half-width of a diffraction peak based on the (111) plane of Li.sub.2S as determined by X-ray powder diffraction measurement is 80 nm or less. The composite exhibits a high capacity (in particular, a high discharge capacity) useful as an electrode active material for a lithium-ion secondary battery (in particular, a cathode active material for a lithium-ion secondary battery), without the need for stepwise pre-cycling treatment.

Transition-metal doped Li-rich anti-perovskite cathode compositions are provided herein. The Li-rich anti-perovskite cathode compositions have a chemical formula of Li.sub.(3-δ)M5/.sub.mBA, wherein 0<δ<3m/(m+1) and δ=3m/(m+1) is the maximum value for the transition metals doping, a chemical formula of Li.sub.4-δMs.sub.δ/mPC.sub.4A, wherein 0<δ≦4m/(m+1) and δ=4m/(m+1) is the maximum value for the transition metals doping, or a combination thereof, wherein M is a transition metal, B is a divalent anion, and A is a monovalent anion. Also provided herein, are methods of making the Li-rich anti-perovskite cathode compositions, and uses of the Li-rich anti-perovskite cathode compositions.