Na-birnessite with high capacity and long cycle life for rechargeable aqueous sodium-ion battery cathode electrodes

Abstract

Layer structure Na-birnessite (Na-Bir) Na_0.58MnO₂·0.48H₂O has been synthesized through a precipitation reaction at room temperature and used as a rechargeable aqueous sodium-ion battery (RASIB) cathode material for the first time. As a RASIB cathode material, the layered Na-birnessite manifests a high specific capacity of 80 mA h g⁻¹ at 1C without obvious capacity loss after 150 cycles. After heat treatment of the Na-Bir sample, it can deliver a specific capacity of 79 mA h g⁻¹ at 1C but only retains 60% of the initial capacity after 150 cycles. The XRD analysis of the Na-Bir sample after 150 cycles reveals that the layer structure is retained, while inductively coupled plasma atomic emission spectroscopy (ICP-AES) indicates that the dissolution of Mn is merely 0.008 wt% of Na-Bir after 150 cycles. As a cathode electrode in full batteries coupled with a NaTi₂(PO₄)₃ anode electrode, a high capacity of 39 mA h g⁻¹ at 10C is obtained with a capacity retention of 94% after 1000 cycles.