Modulating electronic structure to expedite Na4Fe3(PO4)2P2O7 reaction kinetics for high-power Na-ion batteries

Abstract

The Na4Fe3(PO4)(2)P2O7 (NFPP) has considered as a very attractive cathode material for Na-ion batteries mainly due to its cheap price and high security. Its low electron transfer rate is usually improved by coating a layer of hard carbon, which however exhibits a low graphitization degree because of the relatively low NFPP synthesis temperature (~ 500 °C). In this study, a highly-conductive hybrid carbon has been employed to accelerate redox reaction kinetics of NFPP by modulating electronic structure for achieving high-power Na-ion batteries. The hybrid carbon is derived from the mixed polyethylene glycol (PEG) and glucose, in which the low ether bond energy (~ 340 kJ mol−1) of PEG facilitates the free radical generation during pyrolysis with high graphitization degree while glucose improves the uniformity of the carbon coating. As a result, the optimized cathode exhibits a very high reversible capacity of 90.8 mAh g−1 at 20C within 2.0–4.0 V with 85.3% capacity retention after 10,000 cycles, highlighting huge application potentials in two-wheeled electric vehicles, backup energy storage, and so forth.