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,
IEs exhibit 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 the 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 the 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, an increased elastic modulus intensifies the
asymmetry in the EDL response, highlighting the critical interplay
between mechanical elasticity and EDL capacitance in IEs.