Crosslinked Chitosan Networks as Binders for Silicon/Graphite Composite Electrodes in Li-Ion Batteries

Silicon/graphite composites have the potential to improve the practical energy density of Li-ion batteries to enable mass-market penetration of electric vehicles. However, they require polymeric binders that are compatible with both silicon and graphite and can sustain alloying and intercalation reactions as well as the associated interfacial reactions. In this work, chitosan, a natural cellulose, is crosslinked with either molecular (citric acid) or polymeric (poly (acrylic acid), PAA) carboxylic acids to form networks with maximum interaction with the composite as evidenced by infrared spectroscopy. Li-ion half-cells of graphite-rich, silicon/graphite negative electrodes using crosslinked chitosan binders show higher initial Coulombic efficiency (ICE) and more stable cycling performance than pristine chitosan. This could be due to the polymeric network produced from the crosslinking reaction between chitosan and carboxyl acids as well as the strong interactions between polymeric network and surface of silicon and graphite as evidenced by adhesion tests. The crosslinked chitosan network can effectively accommodate large volume change of silicon particles and keep other electrode components connected during cycling as evidenced by scanning electron microscope (SEM) images leading to excellent cycling stability. This makes it very attractive for use as a binder in Si/graphite electrodes for Li-ion batteries. (C) 2018 The Electrochemical Society.