Constructing layer/tunnel biphasic Na0.6Fe0.04Mn0.96O2 enables simultaneous kinetics enhancement and phase transition suppression for high power/energy density sodium-ion full cell

Manganese-based layered compounds NaxMnO2 (0<x <= 1) have been extensively investigated as promising cathode candidates for sodium-ion batteries (SIBs) on account of low toxicity, low cost and high electrochemical activity. However, the unsatisfactory cycling performance of layered structure and low theoretical capacity of tunnel phase cannot meet the requirement of practical applications. Herein, we present the facile Fe doping induced formation of layer/tunnel biphasic compound, i.e. Na0.6Fe0.04Mn0.96O2, which can integrate the advantages of high specific capacity originating from layered structure and excellent cycling/rate performance deriving from tunnel structure, and thus delivers remarkable performance with a high specific capacity of 184.9 mAh g(-1) at 40 mA g(-1) and an impressive capacity retention of 83.1% after 300 cycles at 1000 mA g(-1). The underlying mechanism is deciphered by in-situ X-ray diffraction test, where the eliminated P2-O2 phase transition in biphasic compound could be the possible origin. Importantly, the sodium-ion full cell based on Na0.6Fe0.04Mn0.96O2 and commercial hard carbon delivers excellent cycling performance and high energy density of 186.2 Wh kg(-1)/60.3 W kg(-1). This work not only provides a promising Ni/Co-free cathode candidate with outstanding performance, but also introduces a feasible rationale to effectively enhance performance for layered oxide cathode.