A polymeric mixed conductor-based solid state charge storage device

Abstract

Organic mixed ionic and electronic conductors (OMIECs) are soft materials capable of reversibly storing electronic charges in their bulk, stabilized by ionic charges typically introduced from an electrolyte. Recent advancements in OMIEC design have improved their ion uptake and transport properties, increasing the number of charges stored per monomer unit, thus making them attractive candidates for charge storage devices. However, the use of aqueous electrolytes, common in OMIEC based systems, limit storage performance due to their narrow voltage window. In this work, we introduce an OMIEC-based charge storage device that operates with an ionic liquid gel electrolyte serving as a transparent, solid-state ion reservoir within a full-cell package. This design allows stable operation up to 2.4 V and integrates an embedded failure diagnostics system. To address the critical issue of self-discharge, we incorporated an O₂ and H₂O barrier into the device, significantly improving its performance under ambient conditions. This cell design enables standardized conditions for screening OMIECs, eliminating interference from parasitic reactions or electrolyte instability. Using this system, we systematically evaluated a range of n-type OMIECs and identified the optimal anode material. The resulting device demonstrated a capacity of ∼25 mA h g⁻¹ and an energy density of ∼118 W h kg^−1, surpassing the performance of existing OMIEC-based systems. This work represents a step toward safer and more efficient polymer-based charge storage technologies.