Architecture of imidazolium-based poly(ionic liquid)s–cobalt hexagonal thin nanosheets for high-energy density, using membrane electrolytes†

Abstract

Transition-metal hydroxides have attracted significant interest as electrode materials for supercapacitors due to their abundant redox activity and excellent electrical conductivity. Herein, we present a novel design and engineering of a hexagonal thin nanosheet of cobalt hydroxide (Co(OH)₂) with enveloped imidazolium-based poly(ionic liquid)s (PIL-Br, poly(1-butyl-3-vinylimidazolium bromide)). The presence of PILs in Co(OH)₂ influenced morphogenesis control and a high capacitance of 1758 F g⁻¹ at a current density of 2 A g⁻¹ in a three-electrode system. A solid-state free-standing device was developed with a unique electrolyte configuration comprising EMIM-TFSI/PVDF-HFP, which further enhanced device performance. Achieving a high energy density of 212 W h kg⁻¹ at a power density of 1499 W kg⁻¹ underscored its capability to deliver stored energy effectively. Most notably, the device demonstrated exceptional durability, maintaining a capacity retention of 97% even after undergoing 10 000 cycles at 5 A g⁻¹. Density functional theory also indicated the presence of PILs active sites in the composites, thereby promising a new in situ strategy for energy-storage applications.