Secondary cell with orthorhombic alkali metal/manganese oxide phase active cathode material

An alkali manganese oxide secondary cell characterized by the presence of orthorhombic alkali metal manganese oxide in the active cathode material comprising:

• a) an anode selected from the group consisting of an alkali metal, an alkali metal alloy, carbon, and a carbon-containing material;
• b) an ionically conductive solid separator;
• and
• c) a composite cathode comprising:
• i) an orthorhombic active cathodic material, initially formed as orthorhombic Na.sub.0.44 MnO.sub.2, said orthorhombic cathodic material having the formula M.sub.x MnO.sub.2, where M is one or more alkali metals selected from the group consisting of lithium, sodium, potassium, and mixtures of same, and x ranges from about 0.2 in the fully charged state to about 0.75 in the fully discharged state;
• and
• ii) a solid electrolyte comprising;
• 1) an ionically conductive polymeric material;
• 2) an alkali metal salt;
• 3) carbon;
• and
• 4) a dispersant.

A sodium manganese oxide secondary cell characterized by the presence of orthorhombic sodium manganese oxide in the active cathode material comprising:

• a) an anode;
• b) an ionically conductive solid separator;
• c) an electrolyte;
• and
• d) an orthorhombic active cathodic material, initially formed as orthorhombic Na.sub.0.44 MnO.sub.2.

A lithium manganese oxide secondary cell characterized by the presence of orthorhombic lithium manganese oxide in the active cathode material comprising:

• a) an anode;
• b) an ionically conductive solid separator;
• c) an electrolyte;
• and
• d) an orthorhombic active cathodic material, initially formed as orthorhombic Na.sub.0.44 MnO.sub.2 and then at least partially converted to said orthorhombic lithium manganese oxide by replacing at least a portion of said sodium with lithium without, however, disrupting the orthorhombic structure.