Study of the Electrochemical Intercalation of Different Anions from Non-Aqueous Electrolytes into a Graphite-Based Cathode

Abstract

Different types of carbonaceous materials, such as graphite and carbon black, are typically used as conductive additives in composite electrodes for lithium-ion cells. Since the next generation cathode materials, the so-called 5 V materials like LiCoPO4, operate at potentials above 4.5 V vs. Li/Li+, the issue of anion intercalation into the conductive carbon additive needs to be seriously considered. The anion intercalation from organic-solvent based electrolytes into more graphitic carbons can be accompanied by a solvent co-intercalation reaction, which may lead to the destruction of the graphite structure (graphite exfoliation) and to accelerated electrolyte degradation. These detrimental side reactions may result in a degradation of the overall cathode electrode performance and therefore need to be understood. In this contribution, the electrochemical intercalation of different anions, namely hexafluorophosphate, bis(trifluoromethanesulfonyl) imide and bis(pentafluoroethanesulfonyl) imide, from an organic solvent-based electrolyte into a graphite-based cathode is evaluated with respect to the reversible capacity and coulombic efficiency.