A low-cost and high-rate Na₄Fe₃(PO₄)₂P₂O₇@C cathode material directly used in lithium-ion batteries

Due to its large channels that facilitate the rapid migration of Li⁺, Na₄Fe₃(PO₄)₂P₂O₇ is considered an affordable high-rate cathode material for LIBs. Na₄Fe₃(PO₄)₂P₂O₇@C was obtained using a simple spray-drying method with low-cost Na and Fe starting materials. For the first time, Na₄Fe₃(PO₄)₂P₂O₇@C was directly used as a cathode material in an LIB comprising the LiPF₆ electrolyte and the Li anode. During continuous charge/discharge cycles, the Na⁺ insertion/de-insertion reaction gradually diminished, while the Li⁺ insertion/de-insertion reaction gradually dominated, and the electrode process kinetics became faster, leading to impressive electrochemical properties. The optimized NFPP@MC displayed a high capacity (a reversible capacity of 118.1 mAh g^-1 at 0.1C) and prominent high-rate cycling stability (an average capacity fade rate of 0.015% per cycle at 20C over 1000 cycles). Especially, the reversible capacity of NFPP@MC at 20C reached 74.9% of that at 0.1C. Such prominent high-rate capability was mainly attributed to the large and robust channels in the NFPP framework, which could withstand simultaneous intercalation/de-intercalation of a large amount of Li⁺. The inexpensive raw material, simple and economical synthesis method, and excellent lithium storage performance indicate that Na₄Fe₃(PO₄)₂P₂O₇@C can pave the way for producing low-cost and high-rate cathode materials for LIBs.