Constructing Na-Ion Cathodes via Alkali-Site Substitution

Na-ion batteries have experienced rapid development over the past decade and received significant attention from the academic and industrial communities. Although a large amount of effort has been made on material innovations, accessible design strategies on peculiar structural chemistry remain elusive. An approach to in situ construction of new Na-based cathode materials by substitution in alkali sites is proposed to realize long-term cycling stability and high-energy density in low-cost Na-ion cathodes. A new compound, [K0.444(1)Na1.414(1)][Mn3/4Fe5/4](CN)(6), is obtained through a rational control of K+ content from electrochemical reaction. Results demonstrate that the remaining K+ (approximate to 0.444 mol per unit) in the host matrix can stabilize the intrinsic K-based structure during reversible Na+ extraction/insertion process without the structural evolution to the Na-based structure after cycles. Thereby, the as-prepared cathode shows the remarkably enhanced structural stability with the capacity retention of >78% after 1800 cycles, and a higher average operation voltage of approximate to 3.65 V versus Na+/Na, directly contrasting the non-alkali-site-substitution cathode materials. This provides new insights into alkali-site-substitution constructing advanced Na-ion cathode materials.