Cu/Ti co-doping boosting P2-type Fe/Mn-based layered oxide cathodes for high-performance sodium storage

Environmentally friendly P2 -type layered iron manganese oxides appear to be one of the most potential cathode materials for sodium -ion batteries (SIBs). However, their practical application is hindered by the unfavorable phase transitions, dissolution of transition metals, and poor air stability. One effective strategy by either singlecation doping or high -cost Li involved co -doping is used to alleviate the problems. Here, low-cost Cu/Ti codoping is introduced to boost P2-Na0.7Cu0.2Fe0.2Mn0.5Ti0.1O2 as an air and electrochemical stable cathode material for SIBs. The resulting electrode delivers an initial capacity of 130 mAh g-1 at 0.1C within 2.0-4.2 V, a reversible discharge capacity of 61.0 mAh g-1 at a high rate of 5C and a capacity retention ratio exceeding 71.1% after 300 cycles. In particular, the co -doped crystal structure is well -maintained after 1 month of exposure to air, and even 3 days of soaking in water. Furthermore, the enhancement is elucidated by the effectively mitigated P2-Z and the completely suppressed P2-P ' 2 phase transitions, the decreased volume variation proved by in -situ X-ray diffraction (XRD), as well as the lowered transition -metal dissolution evidenced by inductively coupled plasma optical emission spectrometer (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The low -lost Cu/Ti doping strategy could thus be effective for designing and preparing environmentally friendly and highperformance cathode materials for SIBs.