Scientists have modelled supercapacitor operation at molecular and ionic level

HSE scientists used supercomputer simulations to study the behaviour of ions and water molecules inside the nanopores of a supercapacitor. The results showed that even a very small amount of water alters the charge distribution inside the nanopores and influences the device’s energy storage capacity. This approach makes it possible to predict how supercapacitors behave under different electrolyte compositions and humidity conditions. The paper has been published in Electrochimica Acta. The study was supported by a grant from the Russian Science Foundation (RSF).

Supercapacitors are compact devices capable of rapidly storing and releasing electrical energy. They are used in electronics, hybrid vehicles, energy recovery systems, and solar and wind power plants. Unlike batteries, which require tens of minutes to several hours to charge and typically endure about 500–1,000 cycles, supercapacitors can charge within seconds and withstand hundreds of thousands of cycles without noticeable loss of capacity—the amount of energy the device can store and release. The limitation of supercapacitors is that, despite their speed, they store less energy than batteries of the same size. Therefore, researchers continue to study supercapacitors to find ways of increasing their energy storage capacity.

Previously, a team of researchers from HSE University investigated the behaviour of ions and electrolyte molecules in carbon nanopores and developed a model of the electric double layer. In a new study, scientists from HSE University and the Institute of Solution Chemistry of the Russian Academy of Sciences modelled, for the first time, the behaviour of electrolytes at the level of individual ions and molecules using HSE University's supercomputer. They studied a mixture of an ionic liquid, an organic solvent, and trace amounts of water confined within carbon micropores 0.7–1.9 nanometres wide. Using the molecular and ionic trajectories obtained, the researchers calculated differential capacitance profiles and compared the results with experimental data.

Yury Budkov

'The modelling allowed us to observe how ions and solvent molecules are distributed within the pores, how they form layered structures, and how these layers change with variations in the electrode’s charge,' explains Yury Budkov, Professor at MIEM HSE. 'For the first time, we obtained the differential capacitance of a supercapacitor directly from full-atom molecular dynamics simulations, rather than from simplified theoretical models. This approach allows for more accurate predictions of supercapacitor performance without the need for complex and costly experiments.'

The simulation results showed that even trace amounts of water significantly alter the behaviour of the electrolyte in nanopores. Under a weak negative electrode charge, water disrupted the ordering of ions, thereby reducing the differential capacitance. Conversely, under a strong positive electrode charge, water increased the capacitance: its molecules aligned with the electric field and partially offset the effect of the electrode charge on the ions, thereby altering their distribution within the nanopores.

The scientists also found that changes in capacitance with pore thickness are directly associated with fluctuations in disjoining pressure, the excess pressure within a thin liquid film inside the nanopores. For the first time, it was demonstrated that these fluctuations correspond to changes in the device’s capacitance and reflect how the inner layers of the electrolyte shift and compact when the electrode is charged. This analysis helps explain why, in real supercapacitors, variations in humidity or electrolyte composition can lead to increases or decreases in device performance.

Daria Gurina

'Even small amounts of water impurities can rearrange the internal structure of the electrolyte within the pore and influence charge storage. Understanding these subtle effects is crucial for the development of new electrolytes and electrode materials,' explains Daria Gurina, Research Fellow at MIEM HSE.

The researchers believe that such models will enable more accurate predictions of supercapacitor performance and contribute to the development of more efficient and durable devices for transportation, electronics, and energy storage systems.