Investigation of Graphite Foil as Current Collector for Positive Electrodes of Li-Ion Batteries

We present herein results from a study on replacing the materials for two Li-ion battery (LIB) components: (1) LiPF6 by LiN(SO2CF3)(2) (a.k.a. LiTFSI) as electrolyte in alkyl carbonate based solutions and (2) aluminum foil by graphite foil (a.k.a. Grafoil) as current collector for positive electrodes. LiTFSI may be a better electrolyte than LiPF6 since it does not decompose in water, has increased thermally stability, and its solutions in organic solvents do not contain acidic species detrimental to battery performance. However, since LiTFSI solutions do not passivate aluminum, they must be used with alternative current collectors like Grafoil. We used LiMn0.33Ni0.33Co0.33O2 as active positive electrode material and compared its electrochemical performance and thermal behavior in LiTFSI/EC:DMC when supported by Grafoil with that obtained in LiPF6/EC:DMC when supported by aluminum. We show that LiTFSI solutions can be used together with Grafoil current collectors for positive electrodes with operating potentials below 4.3 V. While significant development efforts to successfully replace aluminum foil by Grafoil in practical Li-ion batteries are still needed, our results indicate that such work may lead to improved battery performance and is therefore worth pursuing. (C) 2013 The Electrochemical Society. [DOI: 10.1149/2.034304jes] All rights reserved.