Effects of Organic Additives on Lithium Insertion/extraction for Graphite Electrode in Ionic Liquid Electrolytes Based on Bis(fluorosulfonyl)imide

Abstract

The electrochemical behavior of a graphitized electrode was investigated in a room-temperature ionic liquid based on bis(fluorosulfonyl)imide (FSI⁻) with the addition of propylene carbonate (PC) or vinylene carbonate (VC). The reversible, significant lithium-ion (Li⁺) insertion/extraction was observed in the additive-free FSI-based ionic liquid, while the additive systems showed weak, reversible responses (VC) and degraded responses (PC). AC impedance measurements suggested that the presence of FSI⁻ extremely reduces the electrode/electrolyte interface impedance, which allows Li⁺ to intercalate into a graphitized electrode reversibly. By contrast, the addition of VC inhibits the reversible Li⁺ intercalation in spite of FSI⁻ existence.