The present invention is to provide a heteroatom-doped nanodiamond, the heteroatom-doped nanodiamond being doped with at least one heteroatom, the heteroatom-doped nanodiamond satisfying criteria (i) and/or (ii) below: (i) a BET specific surface area being from 20 to 900 m.sup.2/g, and (ii) an average size of primary particles being from 2 to 70 nm.

An inorganic solid electrolyte-containing composition contains an inorganic solid electrolyte having an ion conductivity of a metal belonging to Group 1 or Group 2 in the periodic table, a polymer binder, and a dispersion medium, where the polymer binder includes a polymer binder of which an adsorption rate with respect to the inorganic solid electrolyte in the dispersion medium is less than 60%.

A sulfide solid electrolyte particles comprising lithium, phosphorus and sulfur, having a volume-based average particle size measured by laser diffraction particle size distribution measurement of 0.1 μm to 10 μm, having a diffraction peak having 2θ of 29.0 to 31.0 deg in powder X-ray diffraction measurement using CuKα ray, and an intensity ratio (Ib/Ip) of a peak intensity Ib at a high angle-side low part of the diffraction peak to a peak intensity Ip of the diffraction peak is less than 0.09.

The solid electrolyte of the present disclosure includes at least one compound selected from a group including (A) a compound in which a part of Li atom in Li.sub.3PS.sub.4 is substituted with a polyvalent atom (provided that Mg is excluded); (B) a compound in which a part of Li atom in Li.sub.6PS.sub.5X (X: Cl, Br or I) is substituted with a polyvalent atom; and (C) a compound in which a part of Li atom in Li.sub.7P.sub.3S.sub.11 is substituted with a polyvalent atom.

Provided is a material which can be used in a catalyst layer for a fuel cell and exhibits proton conductive properties. The present invention is directed to a carbon-based solid acid comprising a carbon material having a sulfonic acid group through a linker.

A sulfide solid electrolyte contains elemental lithium (Li), elemental phosphorus (P), and elemental sulfur (S). The sulfide solid electrolyte has at least one peak observed in the chemical shift range of 3.4 ppm to 4.8 ppm in a spectrum obtained by .sup.1H-NMR measurement. It is preferable that the sulfide solid electrolyte has an argyrodite-type crystal structure. It is also preferable that the sulfide solid electrolyte contains an ester compound of a carboxylic acid and an alcohol.

An all-solid lithium ion secondary battery has a pair of electrode layers and a solid electrolyte layer between the pair of electrode layers. In the all-solid lithium ion secondary battery, at least one electrode of the pair of electrodes has an active material layer and an intermediate layer on the surface of the active material layer on the side of the solid electrolyte layer, and each of the solid electrolyte layer, the intermediate layer, and the active material layer includes a compound containing Li and two or more shared types of metal elements other than Li, the two or more shared types of metal elements in the solid electrolyte layer, the intermediate layer, and the active material layer are identical between the solid electrolyte layer, the intermediate layer, and the active material layer.

Provided is a high-quality lithium phosphorus complex oxide powder. The lithium phosphorus complex oxide powder comprises Li.sub.1+xM.sup.III.sub.xM.sup.IV.sub.2−x(PO.sub.4).sub.3 (0≤x≤1, M.sup.III represents an element selected from Al, Sc, Cr, Fe, Ga, and In, and M.sup.IV represents an element selected from Si, Ti, Ge, and Zr) and has a concentration of Zn as an impurity of less than 100 ppm.

There is provided an inorganic solid electrolyte-containing composition containing an inorganic solid electrolyte, a polymer binder, and a dispersion medium, where the polymer binder has a constitutional component (X) derived from a polycondensable compound having a polycondensable group and a polymerized chain and has a constitutional component (A) derived from a polycondensable compound having a specific functional group, and the inorganic solid electrolyte-containing composition contains a polymer having a constitutional component (N) containing a nitrogen atom, the polymer having a content of less than 10% by mole in all constitutional components and is dissolved in a dispersion medium. There are also provided a sheet for an all-solid state secondary battery and an all-solid state secondary battery, in which this inorganic solid electrolyte-containing composition is used, and manufacturing methods for a sheet for an all-solid state secondary battery, and an all-solid state secondary battery.

A solid electrolyte for all-solid sodium battery expressed by Na.sub.3-xSbS.sub.4-xA.sub.x, wherein A is selected from F, Cl, Br, I, NO.sub.3, BH.sub.4, BF.sub.4, PF.sub.6, ClO.sub.4, BH.sub.4, CF.sub.3SO.sub.3, (CF.sub.3SO.sub.2).sub.2N, (C.sub.2F.sub.5SO.sub.2).sub.2N, (FSO.sub.2).sub.2N, and [B(C.sub.2O.sub.4).sub.2]; and x is 0<x<3.