Dual-Metal Substitution Enabled NASICON-Type Phosphate Cathodes With Enhanced Electrochemical Activity and Reaction...

Manganese substitution can increase the practical capacities of NASICON-type Na₃V₂(PO₄)₃/C cathodes owing to the high Mn²⁺/Mn³⁺ activity and additional V⁴⁺/V⁵⁺ activation. However, these Mn-substituted NASICON-type cathodes generally suffer from low reaction kinetics and unsatisfactory rate capability. In this study, a Mn/Al dual-metal substitution strategy is utilized to design novel NASICON-type cathodes with enhanced electrochemical performance by incorporating Al atoms into the Mn-substituted Na_3.25V_2.75-xAl_xMn_0.25(PO₄)₃/C (NVAMP/C, 0 ≤ x ≤ 0.2) system. The influence of Al content on the structural and electrochemical properties of the designed NVAMP/C materials is investigated by coupling various physical characterizations and electrochemical measurements. Experimental results reveal that the optimized NVAMP/C composition not only shows greatly high practical capacities of 122.0 mAh g^-1 at 10 mA g^-1 and 103.5 mAh g^-1 at 1000 mA g^-1, but also exhibits robust cycling stability with 81.8% retention after 500 cycles at 100 mA g^-1. Furthermore, combined ex situ X-ray diffraction, galvanostatic intermittent titration technique, and dQ/dV analysis confirm that the Mn/Al dual-metal substitution regulates the phase-evolution mechanism, thereby endowing the material with superior electrochemical reversibility and enhanced reaction kinetics. The finding suggests that the dual-metal substitution strategy is effective in boosting the electrochemical properties of NASICON-type cathodes for advanced sodium-ion batteries.