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 NaTi 2 (PO 4 ) 3 (NTP) phase is introduced into the Na 3 Ti(PO 3 ) 3 N (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.