High-performance crystalline nanocellulose (CNC) supercapacitor separator: Achieved by maximizing alkali-induced gel stress-response prior to aerogel compression forming

Abstract

This study presents the design and fabrication of high-performance separators for supercapacitors based on a novel finding relating to the structural response between alkali ions and cellulose nanocrystals (CNC). Unlike prior art, the CNC-to-ion ratio was specifically chosen following an observed bimodal rheological stress response to applied strain. The stress maximum passed at higher ion concentration was taken to indicate an optimally permeable cellulose cage-structure development, verified by microscopic imaging of the resultant freeze-dried aerogel. The compressed dried structure demonstrates excellent overall performance, including high average nano hardness (∼122 MPa) and ionic conductivity (∼103.5 mS cm⁻¹) after rewetting at 80 w/w% solids content, outperforming commercial borosilicate glass microfiber separator. Benefiting from its hydrophilicity and high porosity, the rehydrated separator demonstrated efficient potassium ion transport. Integrated into symmetric supercapacitor devices with glucose-derived mesoporous carbon electrodes (∼850 m² g⁻¹), the device delivers high specific capacitance (∼80 F g⁻¹ at 10 mV s⁻¹), high energy density (2.7 Wh kg⁻¹ at 98.2 W kg⁻¹), and approximately 95 % capacitance retention after 1000 cycles. These findings suggest that prior rheological identification of optimal structuration during ion addition to CNC in aqueous suspension greatly enhances the suitability of these innovative materials for renewable energy storage applications.