Full-Dimensional Analysis of Electrolyte Decomposition on the Cathode–Electrolyte Interface: Deciphering Electrolyte Degradation Mechanisms on the High-Ni LiNixMnyCo1–x–yO2 Cathode–Electrolyte Interface during the Extreme Fast Charging Process

Ni-rich layered metal oxide cathodes and extreme fast charging (XFC) protocol have been introduced into lithium-ion batteries for the wider adoption of various electric devices. However, nickel intensifies electrolyte decomposition and XFC poses challenges due to extremely high current density. Based on the characterization paradigm established in our previous work, our findings reveal a fundamental difference in the decomposition pathway of the electrolyte under XFC conditions compared to the enhanced reactivity between the oxide and electrolyte caused by Ni content. Specifically, Ni catalyzes solvent dehydrogenation, leading to the formation of protic species that can attack the intermediate, PF5, thereby promoting the decomposition/hydrolysis of LiPF6. But in XFC conditions, the reaction time of dehydrogenation conducted at high voltages is significantly reduced, while conversion of LiPF6 to PF5 lasts throughout the discharging process. Greater accumulation of PF5 as a new initiator changes the solvent decomposition pathway, leading to different cathode–electrolyte interface layers.