Revealing the Self-Doping Defects in Carbon Materials for the Compact Capacitive Energy Storage of Zn-Ion Capacitors

Abstract

Zn-ion capacitors are attracting great attention owing to the abundant and relatively stable Zn anodes but are impeded by the low capacitance of porous carbon cathodes with insufficient energy storage sites. Herein, using ball-milled graphene with different defect densities as the models, we reveal that the selfdoping defects of carbon show a capacitive energy storage behavior with robust charge-transfer kinetics, providing a capacitance contribution of ca. 90 F g −1 per unit of defect density (A D /A G value from Raman spectra) in both aqueous and organic electrolytes. Furthermore, a simple NaCl-assisted ball-milling method is developed to prepare novel graphene blocks (BSG) with abundant self-doping defect density, enriched pores, balanced electric conductivity, and high compact density (0.83 g cm −3 ). The optimized ion and electron transfer paths promote efficient utilization of the self-doping defects in BSG, contributing to improved gravimetric and volumetric capacitance (224 F g −1 /186 F cm −3 at 0.5 A g −1 ) and remarkable rate performance (52.2% capacitance retention at 20 A g −1 ). The defect engineering strategy may open up a new avenue to improve the capacitive performance of dense carbons for Zn-ion capacitors.

Controllable synthesis of electric double-layer capacitance and pseudocapacitance coupled porous carbon cathode material for zinc-ion hybrid capacitors

“…The results show that along with the increase of vacancy concentration, the peak at the Fermi energy level of the material increases significantly, corresponding to the enhancement of the material conductivity. 62–65 In a nutshell, the assembled ZIHCs by SA- x showed an EDLC-pseudocapacitance coupled energy storage mechanism. In addition to the physical adsorption of Zn 2+ on the surface of the SA- x caused by electrostatic action, the pseudocapacitance reaction also occurred due to the presence of oxygen-containing functional groups.…”

Multi‐Channel Hollow Carbon Nanofibers with Graphene‐Like Shell‐Structure and Ultrahigh Surface Area for High‐Performance Zn‐Ion Hybrid Capacitors

“…Furthermore, it is noteworthy that, in addition to the contribution of heteroatoms, structural defects also promote the formation of pseudocapacity. [ 59 ] Considering the high‐density structural defects present in MCHCNF‐ x , a substantial number of active defect sites are available for ion storage, thereby further enhancing its pseudocapacity performance. Notably, the CV profiles of MCHCNF‐2‐based ZIHCs present the largest integrated area among those carbons, demonstrating its highest specific capacity.…”

Sustainable hydrothermal carbon for advanced electrochemical energy storage

“…5 In this context, carbon materials, which are considered promising candidates, have been developed and investigated in electrochemical energy storage applications. [6][7][8][9] With the exploration of diverse carbon materials (such as carbon nanotubes/nanobers, activated carbon, amorphous carbon, graphene, and carbon black materials with controllable characteristics and functionalities) and rapid development of nanotechnology, carbon-based functional materials have received considerable attention. 10,11 However, tedious synthetic methods requiring harsh conditions, organic solvents, 12,13 expensive metal catalysts, 14,15 and complicated apparatus are employed for their preparation, limiting the commercialization of these carbon materials.…”