NASICON-structured Na₃MnTi(PO₄)_2.83F_0.5 cathode with high energy density and rate performance for sodium-ion batteries

NASICON-structured materials with high ionic conductivity, robust structure, and high operation potential have aroused extensive attentions as cathode for sodium-ion batteries (SIBs). However, the poor intrinsic electronic conductivity and low specific capacity are crucial obstacles for practical application of NASICON materials. Herein, a new NASICON-structured Na₃MnTi(PO₄)_2.83F_0.5 (NMTPF-0.5) with the hierarchical and porous structure is synthesized by a simple sol–gel method. The Rietveld refinements and Inductively Coupled Plasma (ICP) chemical analysis confirms the NASICON structure of NMTPF-0.5. The unique structural design significantly enhances rate performance. Meanwhile, the introduction of F^- stimulates electrochemical activities of Mn, and stabilizes crystal structure compared with traditional Na₃MnTi(PO₄)₃. Consequently, the NMTPF-0.5 achieves the high energy density of 511 Wh kg⁻¹ at 0.1C, an outstanding rate performance (364 Wh kg⁻¹ at 10C), and the desirable cycling stabilities exceeding 500 cycles at 10C. The ex-situ XRD reveals the insertion/extraction of Na⁺ through the reversible solid-solution mechanism. Moreover, we statistically analyze how the electrochemical properties and microstructure affected by various F^- substitution amounts. This study explored a novel strategy for designing high capacity and high power-density cathode materials for SIBs via the microstructure and crystal structure optimization.