Provide is a solid electrolyte material consisting of Li, M, X, and F, wherein M is Y, or includes Y and at least one kind selected from the group consisting of metalloid elements and metal elements other than Li; X is at least one kind selected from the group consisting of Cl, Br, and I; two or more peaks are present within a range where a value of a diffraction angle 2 is not less than 24 and not more than 35 in an X-ray diffraction pattern of the solid electrolyte material using Cu-K as a radiation source; one or more peaks are present within a range where the value of the diffraction angle 2 is not less than 40 and less than 48 in the X-ray diffraction pattern of the solid electrolyte material using Cu-K as the radiation source; and two or more peaks are present within a range where the value of the diffraction angle 2 is not less than 48 and not more than 59 in the X-ray diffraction pattern of the solid electrolyte material using Cu-K as the radiation source.

Methods to fabricate tightly packed arrays of nanoparticles are disclosed, without relying on organic ligands or a substrate. In some variations, a method of assembling particles into an array comprises dispersing particles in a liquid solution; introducing a triggerable pH-control substance capable of generating an acid or a base; and triggering the pH-control substance to generate an acid or a base within the liquid solution, thereby titrating the pH. During pH titration, the particle-surface charge magnitude is reduced, causing the particles to assemble into a particle array. Other variations provide a device for assembling particles into particle arrays, comprising a droplet-generating microfluidic region; a first-fluid inlet port; a second-fluid inlet port; a reaction microfluidic region, disposed in fluid communication with the droplet-generating microfluidic region; and a trigger source configured to trigger generation of an acid or a base from at least one pH-control substance contained within the reaction microfluidic region.

A solid electrolyte material contains Li, M, and X. M is at least one selected from metallic elements, and X is at least one selected from the group consisting of Cl, Br, and I. A plurality of atoms of X form a sublattice having a closest packed structure. An average distance between two adjacent atoms of X among the plurality of atoms of X is 1.8% or more larger than a distance between two adjacent atoms of X in a rock-salt structure composed only of Li and X.

A solid electrolyte material contains Li, M, and X. M is at least one selected from metallic elements, and X is at least one selected from the group consisting of Cl, Br, and I. A plurality of atoms of X form a sublattice having a closest packed structure. An average distance between two adjacent atoms of X among the plurality of atoms of X is 1.8% or more larger than a distance between two adjacent atoms of X in a rock-salt structure composed only of Li and X.

A solid electrolyte material is represented by the following compositional formula (1): Li.sub.33+aY.sub.1+aM.sub.aCl.sub.6xyBr.sub.xI.sub.y where, M is at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn; and 1<<2, 0<a<3, 0<(33+a), 0<(1+a), 0x6, 0y6, and (x+y)6 are satisfied.

A solid electrolyte material includes a first crystal phase. The first crystal phase has a composition that is deficient in Li as compared with a composition represented by the following composition formula (1).

Li.sub.3Y.sub.1Cl.sub.6formula (1)

A positive electrode material contains a positive electrode active material and a first solid electrolyte material. The first solid electrolyte material contains Li, M, and X; M at least contains yttrium; and X is at least one selected from the group consisting of Cl, Br, and I.

A solid electrolyte material includes a first crystal phase. The first crystal phase has a composition that is deficient in Li as compared with a composition represented by the following composition formula (1).

Li.sub.3Y.sub.1Br.sub.6formula (1)

A solid electrolyte material includes a first crystal phase. The first crystal phase has a composition that is deficient in Li as compared with a composition represented by the following composition formula (1).

Li.sub.3Y.sub.1Br.sub.6formula (1)

Provided is a solid electrolyte material represented by a composition formula Li.sub.3-3Y.sub.1+-aM.sub.aCl.sub.6-x-yBr.sub.xI.sub.y, where M is at least one element selected from the group consisting of Al, Sc, Ga, and Bi; 1<<1; 0<a<2; 0<(1+-a); 0x6; 0y6; and (x+y)6.