Sodium-Rich Na_3+4xMnTi_1–x(PO₄)₃ Cathode for High-Performance Sodium-Ion Batteries

The low cost, abundant reserves, and wide distribution of sodium resources compared with lithium support the potential for sodium-ion batteries to be widely used in large-scale electric energy storage systems. Na 3 MnTi (PO 4 ) 3 cathode exhibits a three-electron reaction with a theoretical specific capacity of 176 mAh g –1 and high energy density, which indicates its great potential for applications in sodium-ion batteries. Nevertheless, the Jahn–Teller effect of Mn-based materials and the high Na + diffusion energy barrier represent limitations that necessitate further improvement in the structural stability and reaction kinetics of Na 3 MnTi(PO 4 ) 3 . In this work, we successfully prepared sodium-rich Na 3+4 x MnTi 1– x (PO 4 ) 3 materials by adopting a titanium-deficient and sodium-enhanced synthetic strategy. This synthetic strategy significantly increases the number of active Na2 sites and further activates the redox reaction of Mn, thereby improving the electrochemical performance of the material via the analyses by XRD, electrochemical characterization, and DFT calculations. Among the sodium-rich materials, Na 3.2 MnTi 0.95 (PO 4 ) 3 exhibits excellent electrochemical properties with a high reversible capacity (160.5 mAh g –1, 0.2 C), high rate (148.8 mAh g –1, 10 C), and stable cycling performance (capacity retention of 97.6% at 1 C after 100 cycles). The sodium-rich strategy can facilitate the enhancement of the electrochemical performance of polyanionic materials and accelerate their application in the field of sodium-ion batteries.