Improved Electrochemical Reaction of Ni2+-Incorporated NaFe2PO4(SO4)2 as a Cathode Material for Sodium-Ion Batteries

Owing to the natural abundance of sodium, sodium-ion batteries (SIBs) serve as a more cost-effective option compared with lithium-ion batteries (LIBs), while offering comparable energy storage capabilities. This study presents the compositional optimizations, structural characterizations, and electrochemical performance of a new mixed sodium (Na) superionic conductor (NASICON)-type polyanionic material, NaFe 2 PO 4 (SO 4 ) 2 (NFPS). Subsequently, the introduction of Ni 2+ doping serves to simultaneously improve the structural integrity and electronic conductivity of the material, leading to a collective enhancement of the sodium-ion diffusion channels. The Ni 2+ -incorporated phase, NaFe 1.92 Ni 0.08 PO 4 (SO 4 ) 2 , exhibits faster Na + diffusion, resulting in superior rate and cycling performance versus NFPS. After 80 cycles at 25 mA g −1 , NFPS-Ni 0.08 maintains a discharge capacity of 58.7 mA h g −1 , outperforming undoped NFPS by 20%.