Transport and Electrochemical Properties of Na _x Fe _{1– y} Mn _y O ₂ ‐Cathode Materials for Na‐Ion batteries. Experimental and Theoretical Studies

Herein, Na x Fe 1– y Mn y O 2 ( y = 0.4, 0.5, 0.6, 0.7, and 0.8) oxides, which are a potential cathode materials group for Na‐ion batteries, are presented. Samples are prepared by solid‐state synthesis and crystallized in P2‐type structure (P6 3 /mmc). Mössbauer spectroscopy studies revealed that in pristine and deintercalated samples the whole iron occurs at a high‐spin Fe 3+ state. Electrochemical impedance spectroscopy measurements exhibited the thermally activated electrical conductivity of Na 0.67 Fe 1– y Mn y O 2 with relatively high activation energies (≈0.4 eV). Obtained results are supported by the electronic structure calculations (KKR‐CPA method), which indicates that total density of states at the Fermi level increases with manganese content in the sample. Electrochemical properties of Na|Na + |Na x Fe 1– y Mn y O 2 test cells and the specific charge/discharge capacities analysis confirmed that only the manganese ions in Na x Fe 1– y Mn y O 2 are active in electrochemical processes and higher content of manganese results in obtaining higher specific capacities (≈150 mAh g −1 for y = 0.8 under C/10 current load).