posted on 2024-02-20, 21:30authored byBiplab Patra, Keshav Kumar, Subham Ghosh, Madhulika Mazumder, Swapan K. Pati, Premkumar Senguttuvan
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)MnxVyZrz(PO4)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
Na3.5Mn0.75VZr0.25(PO4)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.