To absorb generated hydrogen fluoride and to improve the life characteristic of a battery by adding a Mg.Al.O compound at a specific ratio into the positive electrode mix of the battery containing at least lithium hexafluorophosphate in an electrolyte.

A positive electrode containing lithium manganate (LiMn2O4) as a positive electrode material and negative electrode are wound into a spiral shape via a separator to form an electrode group, the electrode group is inserted into a bottomed cylindrical battery case made of a plated steel, and an electrolyte containing at leans lithium hexafluorophosphate is injected to form an organic electrolyte secondary battery. MgxAlyOz (x≥0, y≥0, x+y=1, z>0), e.g. Mg0.7Al0.3O1.15, is added into a positive electrode mix at 0.2-15 pts.wt. against the total weight of the positive electrode mix. The hydrogen fluoride generated when the lithium hexafluorophosphate reacts with moisture is adsorbed. the deterioration of the lithium, manganate serving as the positive electrode active material is prevented, and the life characteristic is improved.