Significant suppression of exothermic heat flow in silicon anodes via in situ polymerization of phosphonium ionic liquids

Abstract

Silicon anodes, while offering substantially increased energy density in lithium-ion batteries, are prone to interfacial instabilities with liquid electrolytes, leading to the formation of insulating layers, concomitant heat generation, and ultimately, thermal runaway. To address these challenges, novel polymerizable phosphonium ionic liquids (PPILs) were developed as electrolyte additives. These compounds exhibit stability under ambient conditions but undergo polymerization upon electrochemical stimulation. During the initial lithiation process, an in situ polymerization mechanism facilitates the formation of a flame-retardant protective layer on the silicon anode surface. Differential scanning calorimetry (DSC) measurements show that PPILs reduce exothermic heat flow by approximately 92%, demonstrating significantly improved thermal stability. Notably, this enhancement in safety is achieved without compromising critical battery performance metrics, including ionic conductivity, discharge capacity, and cycle life.