Reactivity of Carbonyl-Containing Solid Polymer Electrolytes in Lithium-Metal Batteries from First-Principles Molecular Dynamics

Abstract

Solid polymer electrolytes (SPEs) are promising candidates for all-solid-state Li-metal batteries (ASSLMBs) due to their high safety and excellent mechanical flexibility. However, the widely used polyethers suffer from low ionic conductivity at ambient temperature and unstable electrode-electrolyte interfaces. In this work, we systematically investigate the reactivities with metallic lithium of three carbonyl-containing polymer-based SPE hosts─a polyketone (POHM), a polyester (PCL), and a polycarbonate (PTeMC)─as potential alternatives to polyethers by means of DFT calculations and AIMD simulations. Our redox potential and frontier orbital analyses indicate that introducing alkoxy oxygens connected to carbonyl groups enhances the electrochemical stability of polyester and polycarbonate, but also increases their reactivity on the Li anode surface. In particular, PTeMC shows higher electron uptake and a lower conduction band when interacting with surface Li. This increased reactivity, however, may also promote the formation of a stable solid electrolyte interphase (SEI), preventing further reduction of the electrolyte. We further summarize the possible decomposition mechanisms of the SPE polymer host and predict the resulting SEI components. The simulations revealed that POHM predominantly undergoes α-dehydrogenation and nucleophilic addition-elimination reactions, while PCL exhibits Ccarbonyl-Oalkoxy bond cleavage, producing both saturated and unsaturated lithium alkoxides. In the case of PTeMC, breaking two Ccarbonyl-Oalkoxy bonds can generate two saturated lithium alkoxides and a LixCO species, or it can produce a RCO3Li species and unsaturated hydrocarbons via a Calkoxy-Oalkoxy bond cleavage; these pathways are kinetically favorable and unfavorable, respectively. This work underscores the influence of alkoxy oxygens in carbonyl-containing polymers and provides computational insights for guiding polymer electrolyte design.