Escaping the Polymerization-Kinetics Trap in Ether Electrolytes for Durable Silicon Interphases

Abstract Polymer-rich interphases are widely considered beneficial for silicon (Si) anodes because their mechanical compliance can buffer repeated volume changes. Here, we show that stronger polymerization does not necessarily yield a more durable Si interface. Within a matched pair of cyclic-acetal electrolytes, trioxane exhibits a stronger intrinsic polymerization tendency than dioxolane, yet delivers inferior cycling stability, revealing a polymerization-kinetics trap in which burst-like early-stage polymerization prematurely depletes polymerizable species and drives heterogeneous interphase growth. The introduction of 0.2 M lithium nitrate (LiNO3) yields two complementary effects. NO3– coordination suppresses premature 1,3,5-trioxane (TO) activation, while preferential nitrate reduction enables interphase passivation. Together, these effects reduce sustained electrolyte consumption and promote the formation of a more coherent interphase. This kinetic regulation is supported by cycle-dependent 1H nuclear magnetic resonance (1H NMR) and impedance evolution and yields a thinner, more coherent electrode/electrolyte interface layer. As a result, Si/C anodes retain 81.1% capacity after 400 cycles at 0.5 C, with corresponding full cells retaining 85.4% after 100 cycles.