Graphene-Coated Carbon Nanotube Aerogels Decorated with MnO2 for Ultracompressible and Highly Stable Pseudocapacitors

Electrochemical capacitors (ECs), including supercapacitors and pseudocapacitors, are desirable energy sources for a wide variety of applications. ECs display high power due to their rapid electrochemical kinetics, though pseudocapacitors typically achieve higher energy than supercapacitors due to the presence of faradaic reactions during operation. However, the poor observed lifetime for pseudocapacitors precludes their use in many applications. This poor lifetime comes about due to structural degradation caused by repeated stress on the crystal structure during charging and discharging the electrodes. One route towards suppressing the degradation is by constructing an electrode structure that can tolerate these stresses and alleviate the strain on the pseudocapacitive material.

We have previously developed highly strain-tolerant aerogels by coating a conductive and high surface area single-walled carbon nanotube network¹ with one or more layers of graphene, rendering them ultracompressible and resistant to fatigue.² By decorating these aerogels with a thin layer of MnO₂, we have developed a pseudocapacitor electrode that can undergo large reversible strains without capacitance degradation, ultimately affording high stability and lifetime for the cells.

In this talk, I will present fabrication and structural characterization of graphene-coated carbon nanotube networks decorated with MnO₂, in addition to their electrochemical performance. The electrodes possessed high capacitance in an uncompressed state and when compressed to large strains. Further, the capacitance was recovered fully upon release of the cells because of the robustness of the electrode material. These pseudocapacitors were highly stable, with the capacitive performance and lifetimes being largely unaffected even after ~10,000 compression-release cycles. This work was funded by the National Science Foundation through grants CBET-1335417 and DGE-0966227.

References

1. K. H. Kim, Y. Oh and M. F. Islam, Advanced Functional Materials, 23, 377–383 (2012).

2. K. H. Kim, Y. Oh and M. F. Islam, Nature Nanotechnology, 7, 562–566 (2012).