Polyazopyridine of formula (I) is prepd. by oxidisng 2,5-diaminopyridine hydrochloride salt in H2O and/or an alcohol in the presence of an oxidising agent (n = 5 - 10000).    Also claimed is polyazopyridine doped with a cation and having formula (II) and prepd. by reducing such a polyazopyridine of formula (I) (n = 5 - 10000m n = 0.01 - 2, a = 1, 2 or 3 and X+a is a cation).    The polyazopyridine is prepd. by polymerising chemically 2,5-daminopyridine dissolved in a solvent (pref. H2O) at a concn. of 0.01 - 1 mol/lit. at 20 - 50 deg.C for 0.5 - 16 hrs. in the presence of an oxidising agent (e.g. Na peroxoborate or a mixt. of Na peroxoborate and H3BO3 in a mol. ratio/aminopyridine of 2 - 10. The doped polyazopyridine is formed by pelletising such polyazopyridine, attaching a lead wire to form an electrode and reducing electrolytically the electrode in a soln. contg. a supporting electrolyte contg. an anion (e.g. Na+, Li+, tetraethylammonium ion or tetrabutylammonium ion) and a solvent (e.g. methanol, ethanol, isopropanol, FHF, dioxan, dimethylethylene glycol, propylene carbonate, ethylene carbonate, diethylene carbonate, nitrobenzene, nitromethane, acetonitrile, DMF, DMSO, dimethylphosphoramide, etc.) at a concn. of 0.01 - 1 mol/lit. by constant current process at a current density of -0.01 - 1 Ma/cm2 and constant voltage process under a potential of - 2.4 - -3.0 V (vs. Ag/Ag+) or scanning potential process. Alternately the doped polyazopyridine is formed by reducing chemically polyazopyridine powder by immersing Na phthalide soln. in THF. The sec. cell comprises polyazopyridine as a cathodically active material, electrolyte (e.g., Li tetrafluoroborate, LiC104, LiPF6, tetraethylammonium, BF4, tetrafluoroborate, tetra-butylammonium perchlorate, Li trifluoromethane sulphate, LiI or LiBr) and a solid electrolyte (e.g. AgCl, AgBr, AgI, LiI, RbAg4I5, RbAg4I4N; polyethylene oxide, polypropylene oxide, polyvinylidene fluoride or polyacrylamide).    USE/ADVANTAGE -   The polyazopyridine has high electrochemical activity and stability. It is used for forming a sec. cell having light wt. and high performance.