Ultracompressible, High Rate Supercapacitors from Graphene-Coated Carbon Nanotube Aerogels

The advent of flexible and wearable electronics has led to significant investigation into electrochemical energy sources, in particular electrochemical capacitors (ECs), which can be reversibly deformed without significant loss of performance. There exists a wide array of electrode materials and designs for ECs that are capable of withstanding bending or stretching loads, however very few structures are capable of withstanding significant compressions without loss of properties or plastic deformation. Most successful designs incorporate pseudocapacitive materials like conducting polymers or metal oxides for structural stability, increasing energy but potentially hurting lifetime and capacitance stability of the cells. This work seeks to solve this problem by utilizing an ultracompressible graphene-coated carbon nanotube aerogel as an electrode that possesses a high capacitance and mechanically robust structure without the need for pseudocapacitive materials.

We have previously demonstrated the synthesis of an ultracompressible, superelastic aerogel by coating the struts and nodes of a single-walled carbon nanotube network¹ with one- to few-layer graphene.² These aerogels are capable of withstanding significant (>90%) compressive strain without plastic deformation over many cycles. In addition, they have a highly porous and conductive structure with very large specific surface area, properties which are ideal for supercapacitor applications.

In this talk, I will present fabrication and structural characterization of graphene-coated carbon nanotube aerogels, in addition to their electrochemical performance. The electrodes displayed near-ideal capacitive performance under high-rate operation with no loss of capacitance at 90% compression in both aqueous and room-temperature ionic liquid (RTIL) electrolytes. The transport properties of ions through the electrodes were unaffected by large compressive strains, allowing high-rate operation of cells with both uncompressed and compressed electrodes. Electrochemical impedance spectroscopy investigations confirm that the performance of the supercapacitor electrodes was largely strain-invariant. This performance, in cells with both uncompressed and compressed electrodes, was stable over hundreds of cycles. Moreover, the compression was exploited to construct cells with high volumetric capacitance of ~5 to 18 F/cm³ in aqueous and RTIL electrolytes respectively, nearly 50 times greater than comparable supercapacitor electrodes, while still allowing for rapid charging and discharging of the cells. 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).