A New Sodium‐Based Aqueous Rechargeable Battery System: The Special Case of Na0.44MnO2/Dissolved Sodium Polysulfide

Abstract Herein, the electrochemical performance of a new sodium‐based aqueous rechargeable battery is demonstrated consisting of Na 0.44 MnO 2 as cathode and dissolved sodium polysulfide (i.e., Na 2 S 5 ) as anolyte. Na 0.44 MnO 2 synthesized through a solid‐state reaction method and dissolved Na 2 S 5 anolyte are tested separately in a half‐cell configuration, both giving rise to stable cycling performances. As the anode side of the desired full‐cell configuration is at present dissolved in the electrolyte, the positive and negative electrodes need to be separated with an ion‐selective membrane that is permeable to sodium ions and impermeable to polysulfide species. Hence, Nafion is tested as a barrier to prevent the leakage of the dissolved polysulfides. After careful tuning of the osmotic pressure inside the Nafion membrane, leakage of the dissolved polysulfide from the anode to the cathode side is eliminated, resulting in a 0.8 V average voltage, low‐cost sodium‐ion aqueous cell.