IRON SODIUM HYDROXYSULPHIDE COMPOUND, PROCESS FOR PREPARING SUCH A COMPOUND, ACTIVE MATERIAL COMPRISING SUCH A COMPOUND AND ELECTROCHEMICAL ELECTRODE PRODUCED OF SUCH AN ACTIVE MATERIAL

A process for preparing a compound of formula (NaOH)[Fe(OH)]FeS, may include: (a) mixing iron and sodium sulfide in equimolar amounts, in an NaOH aqueous solution; (b) heating the obtained mixture up to a temperature in a range of from 110 to 210° C. for a duration in a range of from 1 hour to 1 week; and (c) recovering the active material by filtering and drying in a neutral atmosphere.