Li8MnO6: A Novel Cathode Material with Only Anionic Redox

Decoding lithium-ion dynamics: unveiling the role of concentrations and local environments in spinel LixMn2O4

The spinel LiMn2O4 (LMO) offers efficient lithium-ion diffusion channels, yet the mechanisms underlying its transport dynamics remain elusive. In this study, we employ molecular dynamics (MD) simulations, climbing-image nudged elastic band (CI-NEB) calculations, and electronic structure analyses to elucidate the mechanisms governing lithium-ion dynamics in spinel LMO. Our results reveal the critical role of lithium-ion concentrations and asymmetric Mn3+/Mn4+ distributions in modulating diffusion barriers and ion migration pathways. The Jahn-Teller distortions, induced by Mn3+ ions, introduce anisotropic structural changes that significantly alter the energy landscape for diffusion. Notably, we identify a non-linear relationship between the lithium-ion concentration and ionic mobility: low lithium-ion concentrations enable rapid ion transport, while high concentrations increase Coulomb repulsion, hindering diffusion. These findings provide new insights into the coupling of electronic, structural, and ionic properties in LMO, emphasizing the pivotal role of the electronic structure and local environment in optimizing its performance as a cathode material.

Quantifying Effects of Ligand-Metal Bond Covalency on Oxygen-Redox Electrochemistry in Layered Oxide Cathodes

Oxygen-redox electrochemistry is attracting tremendous attention due to its enhanced energy density for layered oxide cathodes. However, quantified effects of ligand-metal bond covalency on the oxygen-redox behaviors are not fully understood, limiting a rational structure design for enhancing the oxygen redox reversibility. Here, using Li₂Ru_1-xMn_xO₃ (0 ≤ x ≤ 0.8) which includes both 3d- and 4d-based cations as model compounds, we provide a quantified relation between the ligand-metal bond covalency and oxygen-redox electrochemistry. Supported by theoretical calculations, we reveal a linear positive correlation between the transition metal (TM)-O bond covalency and the overlap area of TM nd and O 2p orbitals. Furthermore, based on the electrochemical tests on the Li₂Ru_1-xMn_xO₃ systems, we found that the enhanced TM-O bond covalency can increase the reversibility of oxygen-redox electrochemistry. Due to the strong Ru-O bond covalency, the thus designed Ru-doped Li-rich Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode shows an enhanced initial coulombic efficiency, increased capacity retention, and suppressed voltage decay during cycling. This systematic study provides a rational structure design principle for the development of oxygen-redox-based layered oxide cathodes.