Abstract: There is interest in the use of solid-solution electrodes as a way of meeting the problems of conventional batteries; Li.sub.a TiS.sub.2 where O<a<1 is known in this respect and may be made by high temperature preparative routes.Fast ion conductors of the formula A.sub.x M.sub.y O.sub.2 where A is Li, Na or K, M is a transition metal e.g. Co or Ni, <x<1 and y.apprxeq.1 have been made for this purpose according to the invention. They cannot be made by high temperature routes when x is substantially less than 1 owing to stability problems. In the invention, they have been made by electrochemical extraction of A.sup.+ ions from compounds of the formula A.sub.x' M.sub.y O.sub.2 where O<x'<1, carried out at low temperature.