Intercalation-Pseudocapacitive Jarosite Anode for High-Performing Aqueous Lithium-Ion Hybrid Capacitors

Abstract

Aqueous lithium-ion hybrid capacitors (ALIHCs) are considered one of the most sustainable energy storage devices due to their inherent safety and low cost, which generally exhibit both high power density and energy density, benefiting from the combination of capacitive and battery-type electrodes. However, the development of next-generation ALIHCs has long been impeded by the limited availability of suitable pseudocapacitive anode materials. Herein, for the first time, we report jarosite (KFe₃(SO₄)₂(OH)₆) as an anode material for constructing high-performing ALIHCs, which features intercalation pseudocapacitive behavior and rapid electrochemical kinetics, attributed to its intrinsic open-channeled crystal structure as well as nanomorphology. With the optimized 10 m (mol kg^–1) LiCl aqueous electrolyte, the free-standing KFe₃(SO₄)₂(OH)₆ anode with a three-dimensional hierarchically conductive architecture delivers a large pseudocapacitance (207.2 F g^–1), prominent rate capability, and superior cycling stability (∼87.1% after 2000 cycles). Furthermore, when paired with a unique polyacrylamide (PAM)-10 m LiCl hydrogel electrolyte and free-standing K_0.486V₂O₅ cathode, the resulting quasi-solid-state ALIHC demonstrates excellent rate performance, good low-temperature adaptation (∼77.2% capacitance retention at −20 °C), and robust mechanical stability against extreme deformations. Our work presents a great opportunity of developing an inexpensive, new class of intercalation pseudocapacitive anode materials for aqueous lithium storage.