Non-flammable asymmetric electrolyte design for high-voltage lithium-ion batteries

Abstract

Raising the cutoff voltage to 4.4 V offers an immediate route to boost the energy density of stationary storage systems without modifying existing manufacturing lines. Yet this straightforward upgrade is severely constrained by the poor high-voltage stability of current electrolytes, which accelerates cathode degradation and destabilizes the electrode–electrolyte interphase, fuels persistent parasitic reactions, and sharply elevates the risk of thermal runaway. To address the challenges of high operating voltages and thermal runaway, we propose a novel asymmetric fluorinated carboxylate electrolyte by the introduction of highly fluorinated fragments into carboxylate solvents and significant steric hindrance functional group. By manipulating the unique solvation coordination, this strategy suppresses combustion and promotes anion-dominated decomposition. This mechanism facilitates the formation of an inorganic-rich, robust cathode electrolyte interphase (CEI), thereby significantly enhancing the safety and stability of LiNi_0.8Co_0.1Mn_0.1O₂ cathode (NCM811). Crucially, 1.5 Ah Graphite || NCM811 pouch cells with this electrolyte demonstrate cycling performance at 4.4 V, retaining 88% capacity after 700 cycles with an average coulombic efficiency of 99.95% (without thermal runaway during the critical nail penetration test). This work resolves the intrinsic electrochemical incompatibility of non-flammability at the molecular level by regulating Li⁺ solvation, paving the way for high-safety, high-energy-density LIBs.