Abstract: An active material for a positive electrode for lithium secondary batteries and composed of a lithium-manganese oxide (Li.sub.x Mn.sub.2 O.sub.4) with a spinel structure is produced by mixing manganese dioxide with lithium formate (HCOOLi) and/or lithium acetate (CH.sub.3 COOLi), heating the resulting mixture for 10 to 100 hours, preferably at a temperature of from 600.degree. C. to 750.degree. C., and if necessary, grinding the heated mixture. The constituents of the mixture contain manganese and lithium in a molar ratio (Mn:Li) of 2:x, where 0.5<x<1.5. The resulting product has an extremely fine crystallinity and exhibits good cycling stability.

Abstract: Separators for electrochemical high temperature cells with molten electrolytes, particularly consisting of the raw materials boron nitride or aluminum nitride, become better wettable through treatment with boron trifluoride. Preferably the separator, e.g. a BN fabric, may be sprinkled with a BF.sub.3 yielding material, e.g. KBF.sub.4 and activated through brief heating to about 400.degree. C.