High electrochemical energy storage device via cation insertion kinetics in Cs₃Bi₂(Cl_0.5I_0.5)₉@NiO composite electrodes with wide potential window

Surface faradaic process in pseudocapacitor can enable a device that stores higher energy than electrical double-layer capacitors, at higher power delivery than batteries. Yet, most known pseudocapacitive materials exhibit capacitances much less than their predicted values, and possess a low power capability due to their low intrinsic conductivity, in addition to poor cation accessibility. Here, we demonstrate that a bicontinuous Cs₃Bi₂(Cl_0.5I_0.5)₉@NiO composite electrode is able to operate at rates comparable to those of conventional EDLCs; it provide high gravimetric and area normalized capacitances. We present the design of perovskite based electrode designs with improved ion accessibility to redox-active sites, which delivered up to 487 Fg⁻¹ at scan rates of 10 mVs⁻¹ with exceptionally high specific energy density of ∼270 Wh/kg. The electrode architecture enabled us to achieve excellent capacitance retention and power density up to 194 W/g, at rate of 1.0 Vs^-1, with ∼76% contribution from fast surface-controlled (pseudocapacitive) mechanism.