Study on the Li+ Desolvation Mechanism of Doped Carbon Nanotubes and Their Regulatory Effect on the Performance of Organic Supercapacitors

Abstract

Organic supercapacitors (OSCs) suffer from sluggish Li+ desolvation and ion diffusion kinetics, limiting their electrochemical performance and practical application. Heteroatom doping is a valid strategy to improve the capacitive properties of carbon electrode materials. Herein, density functional theory (DFT) first-principles calculations were adopted to systematically investigate and compare the effects of equal-concentration N and P doping on the Li+ desolvation behavior, capacitance performance, and ion diffusion kinetics of single-walled carbon nanotubes (SWCNTs) in acetonitrile-based electrolytes. The results show that N doping maintains the [Li(AN)]+ critical desolvation size (5.91 Å) of pristine SWCNTs, while P doping increases this size to 6.11 Å. Benefiting from the optimized desolvation behavior, P-doped SWCNTs achieve a maximum relative capacitance 1.9 times that of pristine SWCNTs, outperforming N-doped SWCNTs (1.3 times). Moreover, P doping significantly reduces the [Li(AN)]+ diffusion barrier to 0.99 eV, much lower than that of pristine and N-doped SWCNTs, thereby accelerating ion migration. Electronic structure analysis confirms that heteroatom doping weakens electron localization and C-heteroatom covalent bonding, and the weaker P-C bonding further accounts for the superior performance of P-doped SWCNTs. This study clarifies the intrinsic regulatory mechanism of N/P doping on Li+ desolvation and electrochemical performance of SWCNTs, providing a theoretical guideline for the design of high-performance carbon-based electrodes for OSCs.