Organic salts with unsaturated bond and diverse anions as substrates for solid electrolyte interphase on graphite anodes

Abstract

The electrochemical performance of lithium ion batteries is closely related to the solid electrolyte interphase (SEI) film formed on anode surface. Despite the widespread commercialization of graphite anodes, SEI still suffers from unsatisfactory stability, leading to gradual loss of active lithium ions and capacity degradation of batteries. Here organic small molecular salts with unsaturated bonds and diverse anions are coated on graphite particles and work as substrates to form a modified SEI. The CC double bond-containing organic salts, sodium acrylate (SA), sodium vinylsulfonate (SVS) and vinyl sodium phosphate (VSP), possessing carboxylate, sulfonate and phosphate groups, respectively, are rationally selected and their effects on the SEI and electrochemical properties of graphite anodes are systematically investigated. SVS modified graphite generates a SEI film with high flexibility, good compactness and lithium ions conductivity owning to the in-situ polymerization of carbon double bonds and polarity of ionic sulfonate groups. Accordingly, the first coulombic efficiency, rate capability and cycle life of graphite anodes are improved in both half cell and LiNi0·6Co0·2Mn0·2O2-based full cell testing.