Unraveling Inherent Degradation Mechanism of Electrolyte at High-Voltage and the d2sp3 Hybridization Strategy for Non-Flammable 4.8 V LiCoO2 Battery

The potential risk of transition metal (TM) ion dissolution is a prevalent issue in nearly all layered transition metal oxide cathodes. While the detrimental effects of this dissolution are widely discussed in the context of cathode material design, the implications for electrolyte design receive comparatively less attention. In fact, severe decomposition of the electrolyte frequently occurs after the dissolution of TM ions. This phenomenon is typically attributed to the catalytic effects of TM ions. However, there is a lack of research that clearly explains this destabilization of the electrolyte. This study delves into the different interface behaviors between the Co3+ and the Li+. Near the anode surface, a significant proportion of solvent molecules and PF6- ions escape from the Li+ solvation sheath, with only a small portion contributing to the formation of the electrode/electrolyte interface. Subsequently, free Li+ ions are reduced, interpolated or deposited in the anode. In contrast, Co3+ ions exhibit stronger binding ability than Li+ ions, leading to challenges in Co3+ desolvation. Co3+ solvation sheaths demonstrate reduction instability, and trapped solvent molecules and PF6- ions must be reduced. In order to mitigate the hazard of TM dissolution, a fluorinated cathode/electrolyte interface was applied to inhibit the dissolution of TM ions. Isobutyronitrile (IBN) was used to capture harmful Co3+ ions in the electrolyte, resulting in the formation of d2sp3 hybrid orbitals when IBN combines with Co3+. This stable chelated complex effectively eliminated the reduction decomposition associated with Co3+ solvation sheaths. The electrolyte developed through the d2sp3 hybridization strategy effectively addresses the issue of dissolved Co, even when 0.1M Co ions are intentionally added into the electrolyte. LCO batteries utilizing this electrolyte demonstrate an impressive increase in capacity retention, rising from 56.6% to 84.5% after 300 cycles at 4.7 V. Additionally, the capacity retention of LCO battery in this electrolyte is 73.3% after 200 cycles at 4.8 V.