Defect-enriched hydroxyapatite induced by carboxylated chitosan as novel filler for pseudo solid-state supercapacitors

Background: The severe crystalline region in pseudo solid-state polymer electrolyte needs to be addressed to improve the poor ionic conductivity performance. Methods: Hydroxyapatite (HA) with rich defect, induced by carboxylated chitosan (CCS) via hydrothermal process is applied to serve as active filler for pseudo solid-state supercapacitor. Significant findings: CCS2 with high degree of carboxylation (DC) of 42.38% is introduced as defect inducing agents to generate CCS2-HA. CCS2-HA possesses small crystallinity index evaluated by FTIR and XRD. Moreover, the obvious structural defect of CCS2-HA in [301] orientation was observed from HRTEM. With CCS2-HA as defect-enriched filler, the crystallization temperature decreases from 75 to 65 °C. Meanwhile, the activation energy for the ionic conductivity decreases from 2.3 to 1.3 kJ/mol. Meanwhile, the loss tangent peak shifts to higher frequency with smaller intensity in the addition of CCS2-HA as active filler, showing the smaller relaxation time and less heat resistance than the pristine. CCS2-HA possessed rich defects to reduce crystalline region, increase amorphous region, enhance segmental motion, and assist short range ion migration for less internal resistance and heat dissipation as novel filler for superior solid-state energy storage devices.