Nb - doping induces crystallization of coprecipitation particles to achieve high performance sodium-ion batteries cathode materials

Abstract

Sodium-ion batteries (SIBs) are considered as one of the most competitive candidates for energy storage systems. While O3-type NaNi_0.5Mn_0.5O₂ cathode materials offer high theoretical capacity and operating voltage, their practical application is hindered by irreversible phase transitions during Na⁺ extraction/insertion that degrade structural stability and reaction kinetics. This study synthesizes Nb-doped O3-Na[Ni_0.5Mn_0.5]_1-xNb_xO₂ (x = 0,0.01,0.02,0.03) through ball milling assisted coprecipitation. Nb doping enhances lattice stability through two mechanisms: on one hand promoting optimization of coprecipitated particle crystallization, and on the other hand effectively suppressing manganese activity through the formation of mixed cation-oxygen bonds. Na[Ni_0.5Mn_0.5]_0.99Nb_0.01O₂ exhibits 108.7 mAh g^–1 capacity at 0.5C with 77.4 % retention after 200 cycles, demonstrating enhanced cycling stability compared to the undoped material. When paired with hard carbon in full cell, the system achieves >190 Wh kg^–1 energy density. Theoretical calculations also elucidate the mechanism by which Nb doping affects the hybridization of Ni-O bonds, stabilizes the structure of the material, and exhibits enhancement in electrochemical properties. This study provides an effective strategy for suppressing the phase transition and advancing the study of the doping mechanism in sodium-ion batteries.