In Situ Secondary Phase Modified Low-Strain Na₃Ti(PO₃)₃N Cathode Achieving Fast Kinetics and Ultralong Cycle Life

Titanium-based polyanionic materials have attracted extensive studies in recent decades due to their prominent advantages of outstanding structural stability and low cost, which make them promising electrode materials in sodium-ion batteries (SIBs). However, their electrochemical performance is usually limited by an inherently low electronic conductivity. Herein, the NaTi2(PO4)3 (NTP) phase is introduced into the Na3Ti(PO3)3N (NTMN) phase and shows outstanding cycling stability (high-capacity retention of 96.04% at 5 C after 4500 cycles) and enhanced rate performance (∼1.5 times higher capacity in comparison to the undecorated sample at 5 C). Comprehensive in situ/ex situ characterizations reveal an ideal single-phase transition mechanism with a tiny lattice volume distortion (∼0.53%) of NTMN. Density functional theory (DFT) calculations illustrate the Na+ diffusion acceleration mechanism of NTP in the NTMN material. This work provides a promising process to synthesize nitridophosphate materials and offers an effective in situ strategy to improve the electrochemical performance of the as-synthesized materials.