Reducing Structural Distortion by Tailoring Orbital Interactions in High-Voltage Polyanionic Cathodes.

Abstract

The structural distortion of electrode materials in battery systems usually results in the structure degradation and capacity fading upon cycling. However, the fundamental mechanism about the structural distortion remains elusive. A critical issue has emerged concerning the utilization of high-voltage potassium vanadium fluorophosphate compound (KVPO4F) as a competitive cathode material for potassium-ion battery applications. In this work, it is initially identified that the primary distortion in KVPO4F cathode is octahedra distortion. The weak orbital interactions among central transition metal ions with ligands in an octahedron play a pivotal role in the structural distortion, resulting in an accumulation of microstrain during the cycles. This cognition serves as the foundation for the introduction of low energy-level Mn into the V sites to suppress the structure distortion and lattice microstrain. The multi-electron 3d orbitals of Mn sites tend to interact with the σ and π symmetry-matched 2p orbitals of ligands, thereby facilitating the formation of stable octahedrons to endure ion extraction steadily in high voltage. These findings provide a comprehensive understanding of structure degradation based on the octahedral distortion, thereby facilitating the enhancement of stability in high-voltage cathodes.