Densely Packed High-Entropy Spinel Nanoparticles Derived from Concentration-Driven MOF Gel for Lithium-Ion Hybrid Capacitors

Abstract

High-entropy oxides (HEOs) show great potential in supercapacitor due to their unique structural and electronic properties, but precise control of microstructure within these systems still remains a crucial challenge. Herein, a MOF gel synthesis strategy based on gelation kinetics engineering is proposed to tailor the architecture and pore characteristics of high-entropy spinel oxides by tuning the synthesis concentration of the precursor. The influence of gelation kinetics on the microstructure of MOF gel precursors, along with its impact on the morphology, specific surface area, and pore size distribution of the resulting pyrolysis products, was investigated. It was found that MOF gels formed under low-concentration conditions can derive HEOs with more densely packed particles and a hierarchically distributed pore structure. This unique architecture facilitates the establishment of an efficient electron conduction network and ion diffusion pathways, thereby significantly optimizing the electrode kinetics. The optimally structured HEO ((Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 ) 3 O 4 ) delivers a specific capacitance of 636.4 F g -1 at a current density of 1 A g -1 . When assembled as a cathode with activated carbon in a solid-state lithium-ion hybrid capacitor, the device exhibits a broad aqueous voltage window of 1.5 V and a high energy density of 36.6 W h kg -1 at a power density of 750 W kg -1 . This work highlights the potential of gelation kinetics engineering as a promising strategy for developing advanced porous HEOs.