Robust iron-based cathode for ultralong-lasting Na-ion battery with a wide operation-temperature

Abstract

Na4Fe3(PO4)2(P2O7) (NFPP) is an attractive cathode material for sodium-ion batteries (SIBs) due to its low-cost, robust framework, and cross-linked Na+ migrate channels. However, the real implementation of NFPP remains in its infancy, mainly hindered by the inferior intrinsic electronic conductivity. Herein, a doping strategy by incorporating manganese into NFPP lattice (NFMPP) is proposed to lower the band gap and Na+ migrate barriers, thus ultimately rendering robust ligand framework, improved electronic transmission and fast ions diffusion. Greatly, the ultralong-lasting cyclability (88.1% capacity retention for over 10000 cycles at 50 C), impressive rate capability (42.7 mAh g−1 at 200 C), and decent electrochemical performance over a wide operation-temperature range from − 40–60 ℃ are achieved. The structural evolution and charge compensation mechanism during cell operation are systematically explored utilizing in situ X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) measurements, confirming a minimized volume fluctuation and highly reversible Fe2+/Fe3+ redox reaction. Full cell comprising a NFMPP cathode and pre-sodiated hard carbon anode is also yielded as proof of concept. The superior electrochemical performances, and the insertion/extraction mechanism investigation sheds light to the feasibility of utilizing NFMPP as a cathode material for low-cost and high-performance gride-scale energy storage systems (EESs).