(232b) Reaction Mechanisms in LiPF6 carbonate Electrolytes Modified By Phosphorous Pentoxide and Their Effect on Lithium Metal Interface

Rechargeable lithium (Li) metal batteries are the most promising electrochemical energy storage technology to break through the energy density barrier. However, the reductive decomposition and chemical instability of the liquid electrolytes against Li metal result to unstable solid-electrolyte interphase (SEI) formation and porous Li deposition with low coulombic efficiency and severe volume expansion. We demonstrate that the commercial Li-ion battery electrolyte composed of 1 M lithium hexafluorophosphate (LiPF₆) in ethylene carbonate and diethyl carbonate (EC/DEC 50/50 vol. ratio) modified by phosphorous pentoxide (P₂O₅) can significantly improve the cycle stability of Li metal batteries with realistic parameters in 0.4 Ah pouch cells composed of LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) cathode (3 mAh cm^-2) and Li anode (50 mm thick) with a lean electrolyte/capacity ratio of 3 g/Ah. In this presentation, we discuss a number of intertwined and competing reaction mechanisms between P₂O₅ and the electrolyte, revealed by nuclear magnetic resonance (NMR) spectroscopy. We also discuss the methods to control the mechanisms to produce the desirable SEI on Li metal interface with the electrolyte.