Capturing dynamic ligand-to-metal charge transfer with a long-lived cationic intermediate for anionic redox

Biao Li (1) , Khagesh Kumar (2) , Indrani Roy (3) , Anatolii Morozov (4) , Olga Emelyanova (4) , Leiting Zhang (5) , Tuncay Koç (6) , Stéphanie Belin (7) , Jordi Cabana (2) , Rémi Dedryvère (8) , Artem Abakumov (4) , Jean-Marie Tarascon (1)

1 Collège de France - Chaire Chimie du solide et énergie
2 University of Illinois at Chicago
3 University of Illinois at Chicago
4 Skoltech - Skolkovo Institute of Science and Technology [Moscow]
5 PSI - Paul Scherrer Institute
6 SU - Sorbonne Université
7 Beamline SWING, Synchrotron SOLEIL
8 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux

Reversible anionic redox reactions represent a transformational change for creating advanced high-energy-density positive-electrode materials for lithium-ion batteries. The activation mechanism of these reactions is frequently linked to ligand-to-metal charge transfer (LMCT) processes, which have not been fully validated experimentally due to the lack of suitable model materials. Here we show that the activation of anionic redox in cation-disordered rock-salt Li1.17Ti0.58Ni0.25O2 involves a long-lived intermediate Ni3+/4+ species, which can fully evolve to Ni2+ during relaxation. Combining electrochemical analysis and spectroscopic techniques, we quantitatively identified that the reduction of this Ni3+/4+ species goes through a dynamic LMCT process (Ni3+/4+–O2− → Ni2+–On−). Our findings provide experimental validation of previous theoretical hypotheses and help to rationalize several peculiarities associated with anionic redox, such as cationic–anionic redox inversion and voltage hysteresis. This work also provides additional guidance for designing high-capacity electrodes by screening appropriate cationic species for mediating LMCT.

Domaines: Chimie; Chimie analytique; Matériaux

Biao Li, Khagesh Kumar, Indrani Roy, Anatolii Morozov, Olga Emelyanova, et al.. Capturing dynamic ligand-to-metal charge transfer with a long-lived cationic intermediate for anionic redox. Nature Materials, 2022, 21, pp.1165-1174. ⟨10.1038/s41563-022-01278-2⟩. ⟨hal-03705453⟩