ИСТИНА

The mixed polyanionic framework structures, as phosphate-pyrophosphates of sodium and 3d-metals (V, Fe, Co, Mn and Ni), are considered as promising cathode materials for sodium ion batteries due to their superior Na mobility, high operating voltage and thermal stability. The Ni-based cathode material of this family, Na4Ni3(PO4)2P2O7, attracts an attention due to its high operating working potential (appr. 5 V vs. Na/Na+) and the theoretical capacity of 127 mAh·g−1. However, capacity fading of more than 30 % after the 1st cycle hampers the practical application. The substitution in 3d-metal sublattice might enhance the cycling stability due to working potential window shift. This work is devoted to synthesis of Fe-substituted Na4(Ni1-xFex)3(PO4)2P2O7 compounds and to investigation of corresponding electrochemical properties.