• Basile, Andrew
• Omullane, Anthony

Abstract

Designing and characterising a solid-electrolyte interphase using a facile process utilising room temperature ionic liquid electrolytes, allows safe charge-discharge cycling of Li|electrolyte|LiFePO3 batteries for 1,000 cycles with Coulombic efficiencies greater than 99.5%. Lithium metal cyclability is characterised using symmetrical Li|electrolyte|Li cells for 300 cycles at current density of 1.0 mA cm-2 and notably, 5000 cycles at 0.1 mA cm-2. The optimal SEI is prepared using a variety of electrolytes based on the N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide room temperature ionic liquid, exploiting a dynamic time-dependant mechanism which is described herein. The time-dependant SEI formation upon the lithium metal is characterised through a spontaneous morphology modification due to the build-up of passivation products via electrolyte interaction. Importantly, using the pre-treatment no evidence of dendritic growth is observed in full batteries. Scanning electron microscopy clarifies that the different electrolyte formulations provide alternate mechanistic pathways for SEI formation. The results recommend that simple and effective lithium metal pre-treatment through SEI formation using an ionic liquid may enable future lithium metal battery technologies such as lithium-sulphur or lithium-air. The results presented demonstrate commercially viable cycle life for a li-metal battery with no evidence for short circuit through dendrite formation.

Topics

• density
• impedance spectroscopy
• morphology
• scanning electron microscopy
• Lithium
• current density
• Sulphur