Mg-Doping Constructed a Continuous and Homogeneous Cathode-Electrolyte Interphase Film on NaFe(PO) with Superior and Stable High-Temperature Performance for Sodium-Ion Storage.

Sodium-ion batteries (SIBs) are on the verge of achieving practical applications, and the key is to find suitable electrode materials. The polyanionic iron-based material NaFe(PO) (NFPO) possesses an open three-dimensional framework structure with good thermal stability and is regarded as an outstanding cathode material for SIBs. Nevertheless, its poor electrical conductivity, problems with erosion of electrolytes, and structural deterioration during cycling still need to be urgently addressed. Here, we first design a Mg-doped NFPO (NFPO-Mg) material with a dual-action effect. On the one hand, Mg improves the intrinsic conductivity of the NFPO material, and on the other hand, Mg promotes the formation of a homogeneous and stable cathode-electrolyte interphase film during the cycling process, which results in a superior rate performance and cycling stability. A capacity of 68.6 mAh g was achieved at 50C (1C = 117.4 mAh g), and a capacity retention of 79.1% was maintained after 3000 cycles at 20C. More impressively, NFPO-Mg exhibits outstanding high-temperature electrochemical performance, with a capacity retention of 95.3% after 400 cycles at 10C at 60 °C (much higher than the 54.2% for the NFPO). This paper explores an effective method for improving the electrochemical performance of cathode materials, which may prove instrumental in guiding the design of more high-performance cathode materials in the future.