The energy density of supercapacitors - devices similar to batteries but that charge in just seconds to minutes - could be enhanced by increasing the "disorder" within their internal structure.
This finding is highlighted in a study published in
Science, conducted by researchers from the CNRS (CIRIMAT/RS2E) and the Universities of Cambridge and Lancaster. This marks a significant step towards the electrification of urban transportation through supercapacitors.
Similar to batteries, supercapacitors store energy but are able to charge in just seconds to minutes, whereas batteries require considerably more time. A bus, train, or subway using supercapacitors could be fully charged while passengers disembark and board, providing enough energy to reach the next stop.
Thus, there would be no need to install a charging infrastructure along the route. Superconductors are also much more durable than batteries and can withstand millions of charging cycles. However, before these energy sprinters can be widely used, their storage capacity needs to be improved.
To store and release electric energy, a supercapacitor relies on the movement of charged molecules between porous carbon electrodes, which have a highly disordered structure. To visualize the structure of these carbons, imagine a sheet of highly organized graphene that is crumpled. The resulting disorder is similar to that in the materials used for supercapacitor electrodes. However, this disorder complicates the identification and optimization of performance-governing parameters. The size of the nanoscopic pores in the carbon electrodes was long thought to be a key factor.
In a collaboration involving the Inter-university Material Research and Engineering Center (CIRIMAT - CNRS/Toulouse INP/University Toulouse III - Paul Sabatier) and the Universities of Cambridge and Lancaster in England, scientists analyzed a wide range of commercially available nanoporous carbon electrodes and found that the pore size effect observed in some carbons was not universally applicable. The Cambridge team then used nuclear magnetic resonance (NMR) spectroscopy to study this series of electrodes.
Combining NMR spectroscopy analysis and computer simulations help characterize the disorder in porous carbons of supercapacitors and link this parameter to the performance of the materials
© Céline Merlet
These analyses, interpreted through modeling work at CIRIMAT, quantified the level of disorder in each electrode. The results show that the disordered nature of the materials - long considered a flaw - is actually beneficial. The team plans to continue this research to understand why disorder, set during the synthesis of carbon electrodes, is so crucial for ion storage in the nanopores.
These findings, published in
Science, are expected to boost the storage capacity of supercapacitors and promote their widespread use in urban transportation.
The research was partially supported by the Cambridge Trusts, the European Research Council (ERC), and UK Research and Innovation (UKRI).
Writer: AVR
Reference:
Structural disorder determines capacitance in nanoporous carbons
Xinyu Liu, Dongxun Lyu, Céline Merlet, Matthew J. A. Leesmith Xiao Hua, Zhen Xu, Clare P. Grey & Alexander C. Forse.
Science 2024