The invention relates to a highly reactive, high-purity, free-flowing and dust-free lithium sulfide powder having an average particle size between 250 and 1,500 μm and BET surface areas between 1 and 100 m.sup.2/g. The invention, furthermore, relates to a process for its preparation, wherein in a first step, lithium hydroxide monohydrate is heated in a temperature-controlled unit to a reaction temperature between 150° C. and 450° C. in the absence of air, and an inert gas is passed over or through it, until the residual water of crystallization content of the formed lithium hydroxide is less than 5 wt. % and in a second step, the anhydrous lithium hydroxide formed in the first step is mixed, overflowed or traversed by a gaseous sulfur source from the group consisting of hydrogen sulfide, elemental sulfur, carbon disulfide, mercaptans or sulfur nitrides.

A solid electrolyte contains a compound that has a crystal phase having an argyrodite-type crystal structure and that is represented by Li.sub.aPS.sub.bX.sub.c, where X is at least one elemental halogen, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less. The proportion of the crystal phase with an argyrodite-type structure relative to all crystal phases constituting the solid electrolyte is 97.0 wt % or more. The compound has a lattice strain of less than 0.10%. The solid electrolyte preferably exhibits a lithium ion conductivity of 4.0 mS/cm or more.

An electrolytic solution comprising N-(fluorosulfonyl)-N-(fluoroalkylsulfonyl)imide or di(fluorosulfonyl)imide, from which a residual solvent that affects the properties of the electrolyte solution material is reduced, is provided. A method for producing an electrolyte solution material containing fluorosulfonyl imide salt represented by the following general formula (1) and an electrolyte solution preparation solvent comprises decompressing and/or heating a solution containing the fluorosulfonyl imide salt and the electrolyte solution preparation solvent to volatilize a production solvent for the fluorosulfonyl imide salt. ##STR00001## In general formula (1), R.sub.1 represents a fluorine atom or a fluorinated alkyl group having 1 to 6 carbon atoms, R.sub.2 represents an alkali metal ion.

This invention concerns an electrochemical element, in particular a sulphurous solid electrolyte element, comprising a protective casing, as well as modules and batteries comprising such elements.

A solid electrolyte: (compound A) a compound that has a crystal phase having an argyrodite-type crystal structure and that is represented by Li.sub.aPS.sub.bX.sub.c, where X is at least one elemental halogen, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less; and (compound B) a compound that is represented by LiX, where X is as defined above. The compound B has a crystallite size of 25 nm or more. The solid electrolyte preferably has a BET specific surface area of 14.0 m.sup.2/g or less.

A battery includes an anode having an alkali metal as the active material, a cathode having, for example, iron disulfide as the active material, and an increased electrolyte volume.

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 main object of the present disclosure is to provide an all solid state battery wherein interface resistance between a current collector and an active material layer is low. In the present disclosure, the above object is achieved by providing an all solid state battery comprising: an electrode including a current collector, an electron conductive layer, and an active material layer, in this order, and a solid electrolyte layer formed on the active material layer side of the electrode, and the electron conductive layer is an agglutinate of metal particles or a metal foil, and electron conductivity of the electron conductive layer is 1×10.sup.3 S/cm or more at 25° C.

A solid electrolyte includes: (compound A) a compound that has a crystal phase having an argyrodite-type crystal structure and that is represented by Li.sub.aPS.sub.bX.sub.c, where X is at least one elemental halogen, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less; and (compound B) a compound that is represented by LiX, where X is as defined above. The compound B has a crystallite size of 60 nm or less. The solid electrolyte according to the present invention preferably exhibits a lithium ion conductivity at 25° C. of 4.0 mS/cm or more.

A battery includes an anode having an alkali metal as the active material, a cathode having, for example, iron disulfide as the active material, and an increased electrolyte volume.