Current sulfide solid-state electrolyte (SE) membranes utilized in all-solid-state lithium batteries (ASLBs) have a high thickness (0.5˜1.0 mm) and low ion conductance (<25 mS), which limit the cell-level energy and power densities. Based on ethyl cellulose's unique amphipathic molecular structure, superior thermal stability, and excellent binding capability, this work fabricated a freestanding SE membrane with an ultralow thickness of 47 μm. With ethyl cellulose as an effective disperser and binder, the Li.sub.6PS.sub.5Cl is uniformly dispersed in toluene and possesses superior film formability. In addition, ultralow areal resistance of 5.10 Ωcm.sup.−2 and remarkable ion conductance of 190.11 mS (one order higher than the conventional sulfide SE layer) have been achieved. The ASLB assembled with this SE membrane delivers cell-level high gravimetric and volumetric energy densities of 175 Wh kg.sup.−1 and 675 Wh L.sup.−1, individually.

A method for producing a sulfide solid electrolyte, wherein lithium sulfide and a compound represented by the following formula (1) are used as raw materials: PSX.sub.3 (1) (wherein, X is an element selected from F, CI, Br and I.).

An object of the present invention is to provide semiconductor nanoparticles having high quantum efficiency (QY) and a narrow full width at half maximum (FWHM). Semiconductor nanoparticles according to an embodiment of the present invention are semiconductor nanoparticles including at least, In, P, Zn and S, wherein the semiconductor nanoparticles include the components other than In in the following ranges: 0.50 to 0.95 for P, 0.30 to 1.00 for Zn, 0.10 to 0.50 for S, and 0 to 0.30 for halogen, in terms of molar ratio with respect to In.

A sulfide solid electrolyte that can suppress the generation of hydrogen sulfide gas while maintaining the lithium ion conductivity; and an electrode composite material, a slurry and a battery, in each of which the sulfide solid electrolyte is used, are provided. The sulfide solid electrolyte contains lithium (Li), phosphorus (P) and sulfur (S) elements; at least one halogen (X) element; and at least one metal (M) element having a first ionization energy of more than 520.2 KJ/mol and less than 1007.3 KJ/mol, wherein, in an X-ray diffraction pattern measured with CuKα1 radiation, peaks are present at positions of 2θ=25.19°±1.00° and 29.62°±1.00°.

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 main object of the present disclosure is to provide a sulfide solid electrolyte with high ion conductivity. In the present disclosure, the above object is achieved by providing a sulfide solid electrolyte comprising: a Li element, an M element (M is at least one kind of P, Ge, Si and Sn), and a S element, and the sulfide solid electrolyte has an argyrodite type crystal phase, in .sup.31P-MAS-NMR, the sulfide solid electrolyte has peak A at 82.1 ppm±0.5 ppm and peak B at 86.1 ppm±0.5 ppm, and when an area ratio of the peak A is regarded as S.sub.A, and an area ratio of the peak B is regarded as S.sub.B, a proportion of the S.sub.B to the S.sub.A, that is S.sub.B/S.sub.A, is 0.23 or less.

An object is to provide an electrode active material having a novel structure, said electrode active material enabling Li.sub.2S to be used as an electrode. The problem is solved by a solid solution with an antifluorite crystal structure comprising Li, Cu, and S as main constituents.

A negative electrode active material of the present disclosure includes: a graphite particle having a void inside; and a first solid electrolyte. The void has a void size of 1 nm or more and 300 nm or less. The first solid electrolyte is present in the void. The graphite particle has, for example, a plurality of voids inside. The graphite particle has an average void size, determined by a mercury intrusion method, of, for example, 1 nm or more and 300 nm or less.

A method for producing an LGPS-type solid electrolyte can be provided, the method includes preparing a homogeneous solution by mixing and reacting Li.sub.2S and P.sub.2S.sub.5 in an organic solution such that the molar ratio of Li.sub.2S/P.sub.2S.sub.5 is 1.0-1.85; forming a precipitate by adding, to the homogeneous solution, at least one MS.sub.2 (M is selected from the group consisting of Ge, Si, and Sn) and Li.sub.2S and then mixing; obtaining a precursor by removing the organic solution from the precipitate; and obtaining the LGPS-type solid electrolyte by heating the precursor at 200-700° C.

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.