Suppressing Voltage Hysteresis via Multisite Chemical Regulation Toward Stable Sodium Storage in NMTP Cathodes

Abstract

NASICON-type Na3MnTi(PO4)3 is a promising low-cost cathode but suffers from voltage hysteresis and capacity fading. These issues stem from intrinsic Mn2+ antisite defects, which trigger lattice distortion and increase the Na+ diffusion barrier. This structural instability further induces Mn dissolution during cycling, ultimately leading to accelerated capacity decay and hindering practical application. Herein, a rational cation-anion co-doping strategy is proposed to concurrently regulate the local coordination environment and electronic structure of NMTP. High-valent Nb incorporation strengthens the Mn─O framework and alleviates lattice distortion, effectively suppressing voltage hysteresis and enhancing structural stability. Simultaneously, the incorporation of Br− anions enhances Mn─O covalency by facilitating orbital hybridization, owing to the better overlap between the diffuse Br 4p orbitals and Mn 3d orbitals, thereby suppressing Mn dissolution. Benefiting from the synergistic dual modulation, NMTP-Nb&Br exhibits substantially enhanced electrochemical properties, featuring significantly reduced voltage hysteresis, long-term cycling stability with 89.5% capacity retention over 1000 cycles, and improved reversibility. Furthermore, a full cell assembled with a hard-carbon anode achieves a energy density of 310.9 Wh kg−1. This work demonstrates an effective defect-regulation strategy for NASICON-type cathodes and emphasizes the pivotal role of coordinated cation-anion engineering in enabling high-performance and durable sodium storage.