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.
Yi et al. (Wed,) studied this question.