Aqueous rocking-chair aluminum-ion capacitors enabled by a self-adaptive electrochemical pore-structure remolding approach

Abstract

Aluminum ion based electrochemistry offers the advantages of low cost, high safety and, more attractively, three-electron process endowed high energy density, but its kinetics and reversibility have long been restricted by the strong electrostatic field around the bare aluminum ion. Taking hydrated aluminum ions as the charge carriers can well address this issue; however, the large size of hydrated aluminum ions imposes harsh requirements on the pore structures of electrode materials. Herein, we developed an adaptive pore-structure remolding approach for capacitive electrode materials, achieving effective storage of hydrated aluminum ions in a highly compact and ordered manner. Benefiting from the universality of this pore-structure remolding approach, an asymmetric aqueous rocking-chair aluminum-ion capacitor was further constructed, and it exhibited a high operating voltage of up to 2.0 V, an ultrahigh energy density of 112 W h L⁻¹, a high power density of 30 000 W L⁻¹, and a long lifespan over 10 000 charging/discharging cycles. These excellent features distinguish this aluminum-ion capacitor from ordinary aluminum-ion batteries and other state-of-the-art supercapacitors, paving a new way towards aluminum ion based electrochemical energy storage.