Electrochemical Stability Window of Polymeric Electrolytes

The electrochemical stability window (ESW) is a fundamental consideration for choosing polymers as solid electrolytes in lithium-ion batteries. Morphological and chemical aspects of the polymer matrix and its complex interactions with lithium salts make it difficult to estimate the ESW of the polymer electrolyte, either computationally or experimentally. In this work, we propose a practical computational procedure to estimate the ESW due to just one dominant factor, i.e., the polymer matrix, using first-principles density functional theory computations. Diverse model polymers (10) were investigated, namely, polyethylene, polyketone, poly(ethylene oxide), poly(propylene oxide), poly(vinyl alcohol), polycaprolactone, poly(methyl methacrylate), poly(ethyl acrylate), poly(vinyl chloride), and poly(vinylidene fluoride). For each case, an increasingly complex hierarchy of structural models was considered to elucidate the impact of polymer chemistry and the morphological complexity on the ESW. Favorable agreement between the computed ESW of disordered slabs and the corresponding experimental values provides confidence in the reliability of the computational procedure proposed in this work. Additionally, this study provides a baseline for subsequent systematic investigations of the impact of additional factors, such as the presence of lithium salts and electrode electrolyte interfaces. The present work, thus, constitutes an important initial step toward the rational design of novel polymer electrolytes with desired ESW values.