Ammonium perfluorocaprylate - An electrolyte additive for lithium-ion batteries with carbonaceous anodes

Ammonium perfluorocaprylate (APC), a selected additive for lithium-ion batteries has been investigated and exhibited outstanding improvement in the electrochemical performance of carbonaceous anodes. Even with a very low concentration (< 1 wt %) of APC added in 1 M LiPF6/EC:DEC = 1:1 (V/V) electrolyte, a solid interface was formed by APC decomposed products and its own adsorption on the anode surface in the first few charge/discharge cycles. Scanning electron microscopy images confirmed the existence of the solid interface, which is an extraordinarily compact and uniform layer. The formed solid interface greatly inhibited the decomposition of organic electrolytes, and in cyclic voltammetry testing the decomposed peak of organic electrolytes greatly decreased or almost disappeared with the increase of additive concentration because the additive was decomposed in 1.9-1.0 V versus Li/Li+ on the surface of the carbonaceous anode before the organic electrolyte was decomposed at around 0.6 V versus Li/Li+. The major components of the solid interface have been well defined by Raman and Fourier transform infrared analysis. A lower charge-transfer resistance of the carbonaceous anode was determined by electrical impedance spectroscopy in the organic electrolyte system with APC additive. Li-ion battery with APC presented a far greater capacity and pronounced retention capability in long-term testing. (c) 2006 The Electrochemical Society.