Synthesis and electrochemical properties of Na-rich Prussian blue analogues containing Mn, Fe, Co, and Fe for Na-ion batteries

Electrochemical performance of Prussian blue analogues (PBAs) as positive electrode materials for non-aqueous Na-ion batteries is known to be highly dependent on their synthesis conditions according to the previous researches. Na-rich PBAs, NaxM[Fe(CN)6]·nH2O where M = Mn, Fe, Co, and Ni, are prepared via precipitation method under the same condition. The structure, chemical composition, morphology, valence of the transition metals, and electrochemical property of these samples are comparatively researched. The PBA with Mn shows large reversible capacity of 126 mAh g−1 in 2.0-4.2 V at a current density of 30 mA g−1 and the highest working voltage owning to high redox potential of Mn2+/3+ in MnN6 and Fe2+/3+ in FeC6. While, the PBA with Ni exhibits the best cyclability and rate performance though only 66 mAh g−1 is delivered. The significant differences in electrochemical behaviors of the PBAs originate from the various properties depending on different transition metals.