O3-type Na[Fe₁/₃Ni₁/₃Ti₁/₃]O₂ cathode material for rechargeable sodium ion batteries

Na[Fe1 3Ni1 3Ti1 3]O2 cathode material for sodium ion batteries has been synthesized by a solid state reaction method. The obtained Na[Fe1 3Ni1 3Ti1 3]O2 shows an O3 type structure, and delivers a discharge capacity of 117 mAh g 1 under a current density of 10 mA g 1 in a potential range of 1.5 4.0 V at 20 C. Furthermore, the Na[Fe1 3Ni1 3Ti1 3]O2 cathode material shows good rate capability and cycling stability. The structural transition mechanism of the Na[Fe1 3Ni1 3Ti1 3]O2 material is examined by ex situ X ray absorption spectroscopy XAS , Mö bauer spectroscopy and in situ X ray diffraction XRD methods. The Na[Fe1 3Ni1 3Ti1 3]O2 material has almost trivalent iron ions. Iron ions contribute little to the electrochemical activity of the Na[Fe1 3Ni1 3Ti1 3]O2 material. It is observed from the in situ XRD results that the original O3 phase transforms into O amp; 8242;3 and P3 phases during sodium extraction. Moreover, the evolution of the gases evolved during the first charge discharge process is analyzed by an operando mass spectrometry technique. The Na Na[Fe1 3Ni1 3Ti1 3]O2 cell shows an obvious release of CO2 gas at the end of the charge process, which would result in the capacity decay. Nevertheless, the absence of O2 evolution indicates an improved safety of the Na Na[Fe1 3Ni1 3Ti1 3]O2 cell