PNNL

Abstract

We have developed a new method to synthesize polyphenylmethylimine (polyPMI) asa linear or a hyperbranched, conjugated polymer using an aldehyde-imine metathesis reaction.We detail the reaction mechanisms of this polymerization by characterizing a red-shift in itsabsorption spectrum as polymer conjugation length increases and verify that this optical shiftresults from extended p-condensation using density functional theory. This new syntheticapproach provides a polymer that can potentially be depolymerized for facile recyclability and iscompatible with air- and water-sensitive chemistries. As an example of the utility of this newapproach, we demonstrate that this polymer can be directly grown on silicon nanoparticles tocreate silicon anodes for lithium-ion batteries with a high degree of electrochemical interfacialpassivation. These silicon anodes exhibit Coulombic efficiencies above 99.9% and canaccommodate silicon nanoparticle expansion and contraction during lithiation and delithiation asdemonstrated by stable reversible capacities for 500 cycles. Finally, we demonstrate thatpolyPMI facilitates the formation of a lithium fluoride rich solid electrolyte interphase thatremains chemically and mechanically stable after long term cycling.