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 FSL 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 FSL existence.