Tailoring High-Performance Ternary Transition Metal-Based NASICON-Na_{(9–2x–3y–4z)}Mn_xV_yZr_z(PO₄)₃ Cathodes via Combinatorial Chemical Substitutions

Abstract

Sodium superionic conductor (NASICON)-type cathodes are considered promising candidates for long-cycle-life and high-power Na-ion batteries due to their excellent structural stability and Na-ion mobility. While their electrochemical performances have been improved by carbon-coating, particle nanosizing, and chemical tuning strategies, the fundamental understanding of the impact of chemical substitutions is still elusive, which hinders their further development. Herein, we explore a series of micron-sized NASICON-Na (9−2x−3y−4z) Mn x V y Zr z (PO 4 ) 3 [0 ≤ (x, y, z) ≤ 1 and (x + y + z) = 2] cathodes tailored through combinatorial chemical substitutions. Our combined structural and density functional theory studies reveal the complex evolution of (local) crystal and electronic structures, which affects electronic and Na-ion conductivities. Consequently, the Na/V-rich cathodes deliver higher capacities, cycling stabilities, and rate performances compared to those of Na/ Mn-rich compositions. More specifically, the micron-sized Na 3.5 Mn 0.75 VZr 0.25 (PO 4 ) 3 cathode displays excellent capacity retention and rate capabilities (91.6% retention after 200 cycles and 65 mAh g −1 at 5C). This study highlights the importance of tuning the transition metal substitutions to attain high-performance NASICON cathodes.