Sodium-Rich Ferric Pyrophosphate Cathode for Stationary Room-Temperature Sodium-Ion Batteries.

In this article, carbon-coated Na3.64Fe2.18(P2O7)2 nanoparticles (∼10 nm) were successfully synthesized via a facile sol-gel method and employed as cathode materials for sodium-ion batteries. The results show that the carbon-coated Na3.64Fe2.18(P2O7)2 cathode delivers a high reversible capacity of 99 mAh g-1 at 0.2 C, outstanding cycling life retention of 96%, and high Coulomb efficiency of almost 100% even after 1000 cycles at 10 C. Furthermore, the electrochemical performances of full batteries consisting of carbon-coated Na3.64Fe2.18(P2O7)2 nanoparticles as the cathode and commercialized hard carbon as the anode are tested. The full batteries exhibit a reversible capacity of 86 mAh g-1 at 0.5 C and capacity retention of 80% after 100 cycles. Therefore, the above-mentioned cathode is a potential candidate for developing inexpensive sodium-ion batteries in large-scale energy storage with long life.