Highly Flexible and Conductive Cellulose-Mediated PEDOT:PSS/MWCNT Composite Films for Supercapacitor Electrodes

Abstract

Recent improvements in flexible electronics have increased the need to develop flexible and lightweight power sources. However, current flexible electrodes are limited by low capacitance, poor mechanical properties, and lack of cycling stability. In this article, we describe an ionic liquid-processed supramolecular assembly of cellulose and 3,4-ethylenedioxythiophene for the formation of a flexible and conductive cellulose/poly(3,4-ethylenedioxythiophene) PEDOT:poly(styrene sulfonate) (PSS) composite matrix. On this base, multiwalled carbon nanotubes (MWCNTs) were incorporated into the matrix to fabricate an MWCNT-reinforced cellulose/PEDOT:PSS film (MCPP), which exhibited favorable flexibility and conductivity. The MCPP-based electrode displayed comprehensively excellent electrochemical properties, such as a low resistance of 0.45 Ω, a high specific capacitance of 485 F g^-1 at 1 A g^-1, and good cycling stability, with a capacity retention of 95% after 2000 cycles at 2 A g^-1. An MCPP-based symmetric solid-state supercapacitor with Ni foam as the current collector and PVA/KOH gel as the electrolyte exhibited a specific capacitance of 380 F g^-1 at 0.25 A g^-1 and achieved a maximum energy density of 13.2 Wh kg^-1 (0.25 A g^-1) with a power density of 0.126 kW kg^-1 or an energy density of 4.86 Wh kg^-1 at 10 A g^-1, corresponding to a high power density of 4.99 kW kg^-1. Another kind of MCPP-based solid-state supercapacitor without the Ni foam showed excellent flexibility and a high volumetric capacitance of 50.4 F cm^-3 at 0.05 A cm^-3. Both the electrodes and the supercapacitors were environmentally stable and could be operated under remarkable deformation or high temperature without damage to their structural integrity or a significant decrease in capacitive performance. Overall, this work provides a strategy for the fabrication of flexible and conductive energy-storage films with ionic liquid-processed cellulose as a medium.