Effects of network elasticity on asymmetric EDL capacitance-voltage responses of ionoelastomers

Ionoelastomers (IEs) are liquid-free, elastic, single-ion conductors that have emerged as promising solid-state electrolytes for next-generation electrochemical devices. In IEs, one of the ionic species is covalently tethered within an elastic polymer network, whose elasticity strongly influences ion distribution at electrified interfaces. As a result, IE exhibits a unique asymmetric camel-shaped capacitance–voltage profile of the electric double layer (EDL). In this study, we investigate the effect of network elasticity in IEs on the EDL capacitance response as a function of applied voltage. We observe a correlation between the elastic energy of IEs and EDL capacitance, where higher elasticity appears to limit the long-range movement of crosslinked ion species toward charged interfaces. In networks with low storage moduli, the soft elasticity permits dense interfacial accumulation of tethered ion species similar to untethered ions, resulting in a symmetric camel-shaped EDL capacitance profile. In contrast, highly crosslinked networks with increased elasticity suppress such accumulation, resulting in an asymmetric capacitance-voltage response between crosslinked ions and their mobile counterions. Furthermore, the asymmetric EDL capacitance voltage response of IEs can be modulated by temperature, as the elastic modulus of the polymer network is strongly temperature-dependent. At lower temperatures, increased elastic modulus intensifies the asymmetry in the EDL response, highlighting the critical interplay between mechanical elasticity and EDL capacitance in IEs.