(418h) Molecular Insights on the Performance of Nanoporous Carbide-Derived Carbon Supercapacitors with Various Electrolytes

Supercapacitors, also known as electric double layer capacitors (EDLCs), have drawn increasing interest due to their rapid charging capability and long cycle lifetimes. This charge storage mechanism has no solid phase transport limitations, leading to high power density. However, EDLCs have lower energy density than batteries since the charge is confined to the electrode surface. To improve the energy density of supercapacitors without sacrificing power density, it is desirable to better understand the charging behavior of supercapacitors and discover novel materials for electrolytes and electrodes.

Carbide-derived carbon (CDC) electrodes are high-surface-area nanoporous materials, and ion desolvation happens in CDC pores smaller than the solvated ions, which dramatically improves the capacitance of CDC supercapacitors. Fundamental research has been done to uncover the molecular phenomena and mechanism, but molecular studies for different electrolytes in CDC supercapacitors have not been reported. We use all-atom models to describe each molecule in the system, as opposed to coarse-grained models, which allows us to study different electrolytes and capture explicit atom-atom interaction information. We consider several promising electrolytes. For example, ionic liquid/organic solvent mixtures exhibit higher ion conductivity while retaining relatively wide electrochemical voltage stability windows. In addition, solvent-in-salt (SIS) electrolytes (i.e., highly concentrated salt solutions) are promising for next-generation high-energy density supercapacitors and batteries due to their expanded voltage windows, nonflammability, and lack of volatility. We use constant potential molecular dynamics to investigate the effects of these electrolytes on charging dynamics and charge storage of realistically modeled CDC supercapacitors. This yields molecular insights into the charging dynamics and charge storage mechanism of supercapacitors with different electrolytes, allowing us to select novel electrolytes or electrodes to improve supercapacitor performance.