This invention relates to new chemical compositions, and more particularly to double chromates having the formula MM'(CrO.sub.4).sub.2 or MM'(Cr.sub.2 O.sub.7).sub.2 or MM' (CrO.sub.x).sub.2 where M and M' represent different metals and where x is less than 4 and greater than or equal to 3.7, to methods of making them, and to their use as positive active materials in batteries.
From the disclosure of French Pat. No. 2 110 765, a lithium battery is known having a nonaqueous electrolyte and positive active material constituting silver chromate having the formula Ag.sub.2 CrO.sub.4. One of the great interests in this type of battery is that the reduction in metallic silver occurs, with sufficiently small currents, at a level of about 3 volts, with good yield and stability, so that such a battery can be used in applications such as clocks or cardio-stimulators. This active material has given fully satisfactory results, but it is relatively expensive.
Other chromates have been proposed as the active positive material for batteries, for example, chromates of copper, of iron, of cobalt, of nickel, of mercury, of thallium, and of bismuth, but aside from the fact that the existence of certain of these chromates is doubtful, their stability and discharge voltage would be inferior to the above-mentioned silver chromate.