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

The use of orthorhombic Na x MnO 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 + or Na + ) per manganese at moderate current densities, corresponding to capacities of 160 to 180 mAh/g. Li / PEO / Na 0.2 Li x MnO 2 cells [ PEO = poly ( ethylene oxide ) ] to date have been cycled over ninety times at 0.1 mA/cm 2 , with excellent capacity retention. Na / PEO / Na x MnO 2 and Na x MnO 2 / PEO / Na x MnO 2 cells have been cycled over sixty times to date at the same rate, showing moderate capacity fading.