Li-doping stabilized P2-Li0.2Na1.0Mn0.8O2 sodium ion cathode with oxygen redox activity

The discovery of the oxygen chemistry phenomenon reveals bright future toward new sustainable layered Na-based transitional oxides. However, the poor capacity retention problem of the cathode has hindered the development of sodium ion batteries (SIBs). In this work, a new Li-doped compound Li0.2Na1.0Mn0.8O2 is proposed, which demonstrates refined cycling durability with 51.6% after 100 cycles at 50 mA g(-1), superior than Na1.2Mn0.8O2 with only one cycle. Then in situ X-ray diffraction (XRD) and density function theory (DFT) are employed to explore the lattice distortion and confirm stable lattice framework introduced by Li atoms with eliminated P2-O2 phase transition upon cycling, guaranteeing outstanding electrochemically stable performance. In addition, Li0.2Na1.0Mn0.8O2 demonstrates activation of Mn as well as O chemistry redox in the lattice, detected by ex situ electronic paramagnetic resonance spectroscopy (EPR) as well as in situ Raman, which indicate not only Na-deficient Mn-based layered oxide but also Na-rich Mn-based compound can represent oxygen redox.