Exploring the Impact of Minor Water Content on Polymer Electrolytes with Molecular Dynamics

Solid-state polymer electrolytes (SPEs) are increasingly favored over liquid electrolytes for emerging energy storage devices due to their safety features, enhanced stability, and multifunctionality. Minor solvents (such as water) are often introduced unintentionally or intentionally into SPEs. Although it can significantly affect SPEs' electrochemical and mechanical properties, the fundamental role of such solvent content has rarely been studied. Here, we investigate the effects of minor water content on two representative SPEs through molecular dynamics simulations. Focusing on SPEs composed of different base polymers, namely, poly(ethylene oxide) (PEO) and poly(lactic acid) (PLA), and the same salt, lithium perchlorate (LiClO4), our simulations reveal that slight hydration facilitates an increase in ionic conductivity while preserving the mechanical integrity of the SPEs. Notably, these water contents appear to affect ionic conductivity more effectively in certain systems than others, which is attributed to the unique interactions among ions, water, and the polymer matrix. Moreover, small amounts of water can maintain the stiffness of SPEs rather than reducing it. Such results suggest a facile approach to developing SPEs with balanced ionic conductivity and mechanical properties, suitable for a range of energy storage applications.