A positive electrode material for a secondary battery, wherein the positive electrode material includes a triclinic crystal structure.

A positive electrode material for a secondary battery, wherein the positive electrode material includes a triclinic crystal structure.

A method of restoring the proton conductivity of a sintered pyrophosphate membrane of intermediate temperature fuel cells (IT-FCs) by introducing phosphoric acid into the sintered SnP.sub.2O.sub.7 membrane to react with the degraded SnP.sub.2O.sub.7 species and thus restore the membrane pyrophosphate and proton conductivity. Such cells operate with low external humidification, and the active area of the cells may be fabricated up to 100 cm.sup.2 in size.

A method of restoring the proton conductivity of a sintered pyrophosphate membrane of intermediate temperature fuel cells (IT-FCs) by introducing phosphoric acid into the sintered SnP.sub.2O.sub.7 membrane to react with the degraded SnP.sub.2O.sub.7 species and thus restore the membrane pyrophosphate and proton conductivity. Such cells operate with low external humidification, and the active area of the cells may be fabricated up to 100 cm.sup.2 in size.

A positive electrode material for a secondary battery, wherein the positive electrode material includes a triclinic crystal structure and is represented by Li.sub.4+x(Fe.sub.1zM.sub.z).sub.40.5x(P.sub.2O.sub.7).sub.3, where 0.65x0.75, 0.0<z0.7, and M represents a divalent metal other than Fe.

A positive electrode material for a secondary battery, wherein the positive electrode material includes a triclinic crystal structure and is represented by Li.sub.4+x(Fe.sub.1zM.sub.z).sub.40.5x(P.sub.2O.sub.7).sub.3, where 0.65x0.75, 0.0<z0.7, and M represents a divalent metal other than Fe.

A positive electrode (21) includes a positive electrode current collector (21A), and a positive electrode mixture layer (21B) which is formed on the positive electrode current collector (21A) and contains a positive electrode active material. The positive electrode mixture layer (21B) includes a first positive electrode active material (21B-1) composed of LiVPO.sub.4F and a second positive electrode active material (21B-2) composed of LiVP.sub.2O.sub.7. In addition, a mixing ratio of the first positive electrode active material (21B-1) and the second positive electrode active material (21B-2) contained in the positive electrode mixture layer (21B) is represented by (1x)LiVPO.sub.4F+xLiVP.sub.2O.sub.7 (x is a mass ratio, 0<x0.21).

A method for the manufacture of crystal water-free iron(II) orthophosphate of the general formula Fe.sub.3(PO.sub.4).sub.2 or crystal water-free iron(II) metal orthophosphate, iron(II) metal pyrophosphate or iron(II) metal metaphosphate of the general formula Fe.sub.aMet.sub.b(PO.sub.c).sub.d, where a is a number from 1 to 5, b is a number from >0 to 5, c is a number from 2.5 to 5, d is a number from 0.5 to 3 and Met represents one or more metals selected from the group consisting of K, Rb, Cs, Mg, Ca, Sr, Ba, the transition metals (d block), in particular Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Mn, Cu, Zn and the metals and semimetals of the third, fourth and fifth main groups, in particular B, Al, Ga, In, Si, Sn, Sb, Bi and the lanthanoids.

A method for the manufacture of crystal water-free iron(II) orthophosphate of the general formula Fe.sub.3(PO.sub.4).sub.2 or crystal water-free iron(II) metal orthophosphate, iron(II) metal pyrophosphate or iron(II) metal metaphosphate of the general formula Fe.sub.aMet.sub.b(PO.sub.c).sub.d, where a is a number from 1 to 5, b is a number from >0 to 5, c is a number from 2.5 to 5, d is a number from 0.5 to 3 and Met represents one or more metals selected from the group consisting of K, Rb, Cs, Mg, Ca, Sr, Ba, the transition metals (d block), in particular Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Mn, Cu, Zn and the metals and semimetals of the third, fourth and fifth main groups, in particular B, Al, Ga, In, Si, Sn, Sb, Bi and the lanthanoids.

The present invention relates to a positive electrode active material for a potassium secondary battery, the positive electrode active material according to the present invention is a crystalline material comprising: K; a transition metal; P; and O, and comprises, as a main image, an image indicating a diffraction peak having a relative intensity of 5% or more in a range of Bragg angles (2) of a X-ray diffraction pattern of 14.7 to 15.7, 22.1 to 23.1, 25.5 to 26.5, and 29.7 to 30.8, when the relative intensity of the diffraction peak having the highest intensity is taken as 100% in the powder X-ray diffraction pattern of the material.