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

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.