Rechargeable Na-MnO2 battery with modified cell chemistry

High voltage, high energy density, nominal cycle life, and low cost are the most critical requirements of rechargeable batteries for their widespread energy storage applications in electric vehicles and renewable energy technologies. Na-MnO2 battery could be a low-cost contender, but it suffers extensively from its low cell voltage and poor rechargeability. In this study, we modified the conventional cell structure of Na-MnO2 battery and established altered cell chemistry through a hybrid electrochemical process consisting of Na striping/plating at the anode and Zn2+ insertion/de-insertion along with MnO2 dissolution/deposition at the cathode. After the modification, Na-MnO2 battery exhibits a discharge capacity of 267.10 mA h/g and a cell voltage of 3.30 V (vs. Na/Na+), resulting in a high specific energy density of 881.43 Wh/kg. After 300 cycles, the battery retains 98% of its first-cycle discharge capacity with 100% coulombic efficiency. Besides, Na metal-free battery assembled using sodium biphenyl as a safer anode also delivers an excellent energy density of 810.0 Wh/kg. This work could provide a feasible method to develop an advanced Na-MnO2 battery for real-time energy storage applications.