Mn-Doped Na₄Fe₃(PO₄)₂P₂O₇ as a Low-Cost and High-Performance Cathode Material for Sodium-Ion Batteries

Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) is considered to be an ideal cathode material for sodium-ion batteries due to its high theoretical capacity, stable structure, small volume change, low cost, and nontoxicity. However, the inherent low electronic conductivity of polyanionic materials limits the application of this material. In this work, we improved the electronic conductivity and structural stability of the material through a dual modification synergistic strategy of manganese ion doping and surface carbon coating and prepared Na₄Fe_2.9Mn_0.1(PO₄)₂P₂O₇@C (0.1 Mn-NFPP@C) composites by a simple mechanical-assisted chemical synthesis method. It can release 119.6 mAh g^–1 at 0.1C. The capacity retention rate is 97.4% after 100 cycles at 1C and 84.8% after 3000 cycles at 10C. Many tests and calculations in this work also show that 0.1 Mn-NFPP@C modified by Mn²⁺ doping and carbon coating has higher electronic conductivity and electrochemical kinetics and thus exhibits better electrochemical performance.