α/β–Type NaMn0.89Ni0.11O2: as high-performance sodium-ion battery cathode

Sodium-ion batteries (SIBs) are an exciting alternative to commercially dominant lithium-ion batteries for electric vehicles and other applications. However, cathodes of SIBs suffer poor kinetics, low average potential, and poor rate capability due to the large ionic radius of Na+–ions. We report an α- and β-type composite NaMn0.89Ni0.11O2 cathode with excellent electrochemical performance. The designed electrode shows a discharge capacity of 100.1 mAh g−1 with a capacity retention of about 69% and Coulombic efficiency of 98.9% even after 100 cycles at 0.05C. The diffusion coefficient of the electrode material lies in an impressive range of values of 10−06–10−11 cm2 s−1 over the state of charge. The α-phase helps get a higher diffusion coefficient, and the β-phase diminishes Jahn–Teller distortion arising from the Mn3+/4+ oxidation process, exploiting both phases’ compositional and structural tolerance. The β-phase increases cycle life, and the α-phase increases kinetics. Accessing the Ni2+/4+ oxidation process increases the electrodes’ average operating potential. The NaMn0.89Ni0.11O2 // HC full cell gives an average potential of 2.7 V when cycled in the potential range of 1.5–3.2 V.