Orthorhombic Na x MnO2 as a Cathode Material for Secondary Sodium and Lithium Polymer Batteries

The use of orthorhombic Na[sub x]MnO[sub 2] as a cathode material for alkali metal polymer electrolyte batteries is described for the first time. This sodium manganese bronze has a tunnel structure and can reversibly intercalate up to 0.55 to 0.6 alkali metal ions (Li[sup +] or Na[sup +]) per manganese at moderate current densities, corresponding to capacities of 160 to 180 mAh/g. Li/PEO/Na[sub 0.2]Li[sub x]MnO[sub 2] cells [PEO = poly(ethylene oxide)] to date have been cycled over ninety times at 0.1 mA/cm[sup 2], with excellent capacity retention. Na/PEO/Na[sub x]MnO[sub 2] and Na[sub x]MnO[sub 2]/PEO/Na[sub x]MnO[sub 2] cells have been cycled over sixty times to date at the same rate, showing moderate capacity fading.