Suppressing Intrinsic Anti‐Site Defects via Targeted Li‐Occupation Unlocks Ultrahigh‐Rate Capability in Vanadium‐Free NASICON Cathodes

Abstract

ABSTRACT Vanadium‐free Na superionic conductor (NASICON)‐type Na 3 MnTi(PO 4 ) 3 (NMTP) has been recognized as a prospective cathode material for sodium‐ion batteries owing to the abundance of raw materials, and its eco‐friendly composition. Yet the intrinsic anti‐site defects (IASDs) derived from the occupation of Mn 2+ on the Na‐vacancy site (Mn/M2_v) in NMTP severely deteriorates the Mn redox kinetics, causing abnormal voltage hysteresis and unsatisfactory rate performance. This study rationally designed a targeted Li‐occupation to effectively restrain the Mn/M2_v IASDs formation. Theoretical calculations identify that the tiny Li + ions preferentially occupy the alkali‐metal vacancies instead of Mn 2+ and selectively occupy M2 (18 e )‐sites rather than M1 (6 b )‐sites, thereby effectively inhibiting anti‐site occupation of Mn 2+ . This is experimentally validated in the prepared Na 2.95 Li 0.05 MnTi(PO 4 ) 3 (NMTP‐Li0.05), where minimal Li doping leads to significant suppression of Mn/M2_v IASDs. During charge‐discharge, the introduced Li + exhibits high mobility between M1/M2 sites and low electrostatic repulsion with Na + . Therefore, the NMTP‐Li0.05 achieves promoted kinetics with eliminated voltage hysteresis and an ultrahigh‐rate capability of 70.2 mA h g −1 at 100 C, which is exceptional among V‐free NASICON cathodes. This work establishes an effective strategy for IASDs suppression in polyanionic cathodes and paves the way for developing high‐performance and sustainable sodium‐ion batteries.