P2-Type Na<sub>0.84</sub>Li<sub>0.1</sub>Ni<sub>0.27</sub>Mn<sub>0.63</sub>O<sub>2</sub>-Layered Oxide Na-Ion Battery Cathode: Structural Insights and Electrochemical Compatibility with Room-Temperature Ionic Liquids
Arianna Massaro, Gabriele Lingua, Francesco Bozza, Alessandro Piovano, Pier Paolo Prosini, Ana B. Muñoz‐García, Michele Pavone, Claudio Gerbaldi
Abstract
High Resolution Image Download MS PowerPoint Slide Modern technologies that can replace state-of-the-art Li-ion batteries (LIBs), such as Na-ion batteries (NIBs), are currently driving new advancements in energy storage research. Developing functional active materials having sustainable features and enhanced performances able to assess their exploitation in the large-scale market represents a major challenge. Rationally designed P2-type layered transition metal (TM) oxides can enable high-energy NIB cathodes, where the tailored composition directly tunes the electrochemical and structural properties. Such positive electrodes need stable electrolytes, and exploration of unconventional room-temperature ionic liquid (RTIL)-based formulations paves the route toward safer options to flammable organic solvents. Notwithstanding the fact that Li + doping in these materials has been proposed as a viable strategy to improve structural issues, an in-depth understanding of structure–property relationship as well as electrochemical testing with innovative RTIL-based electrolytes is still missing. Herein, we propose the solid-state synthesis of P2-Na 0.84 Li 0.1 Ni 0.27 Mn 0.63 O 2 (NLNMO) cathode material, which exhibits promising structural reversibility and superior capacity retention upon cycling when tested in combination with RTIL-based electrolytes (EMI-, PYR 14 -, and N 1114 -FSI) compared to the standard NaClO 4 /PC. As unveiled from DFT calculations, lattice integrity is ensured by the reduced Jahn–Teller distortion upon Na removal exerted by Mn 4+ and Li + sublattices, while the good redox reversibility is mainly associated with the electrochemically active Ni 2+ /Ni 3+ /Ni 4+ series burdening the charge compensation upon desodiation. By declaring the electrochemical compatibility of the P2-NLNMO cathode with three RTIL-based electrolytes and dissecting the role of Li/Ni/Mn sublattices in determining the electrochemical behavior, our comprehensive study enlightens the potential application of this electrode/electrolyte setup for future high-energy NIB prototype cells.