Manganese Dioxide Decoration of Macroscopic Carbon Nanotube Fibers: From High-Performance Liquid-Based to All-Solid-State Supercapacitors

TL;DR

This paper reports the fabrication of flexible, high-performance supercapacitors using MnO2-decorated carbon nanotube fibers, demonstrating high energy and power densities in both liquid and solid electrolytes for portable applications.

Contribution

It introduces a novel method to decorate macroscopic carbon nanotube fibers with MnO2 nanoparticles for all-solid-state supercapacitors without metallic current collectors.

Findings

Achieved high specific energy of 36 Wh/kg in liquid electrolyte supercapacitors.

Demonstrated maximum energy density of 21 Wh/kg in solid-state supercapacitors.

Supercapacitors showed excellent cycling stability and high power density.

Abstract

Supercapacitors capable of providing high voltage, energy and power density but yet light, low volume occupying, flexible and mechanically robust are highly interesting and demanded for portable applications. Herein, freestanding flexible hybrid electrodes based on MnO2 nanoparticles grown on macroscopic carbon nanotube fibers (CNTf-MnO2) were fabricated, without the need of any metallic current collector. The CNTf, a support with excellent electrical conductivity, mechanical stability, and appropriate pore structure, was homogeneously decorated with porous akhtenskite \epsilon-MnO2 nanoparticles produced via electrodeposition in an optimized organic-aqueous mixture. Electrochemical properties of these decorated fibers were evaluated in different electrolytes including a neutral aqueous solution and a pure 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid (PYR14TFSI). This comparison helps discriminate the various contributions to the total capacitance: (surface) Faradaic and non-Faradaic processes, improved wetting by aqueous electrolytes. Accordingly, symmetric supercapacitors with PYR14TFSI led to a high specific energy of 36 Whkg_(MnO_2)^(-1) (16 Whkg-1 including the weight of CNTf) and real specific power of 17 kWkg_(MnO_2)^(-1) (7.5 kWkg-1) at 3.0 V with excellent cycling stability. Moreover, flexible all solid-state supercapacitors were fabricated using PYR14TFSI-based polymer electrolyte, exhibiting maximum energy density of 21 Whkg-1 and maximum power density of 8 kWkg-1 normalized by total active material.