Influences from solvents on charge storage in titanium carbide MXenes

Pseudocapacitive energy storage in supercapacitor electrodes differs significantly from the electrical double-layer mechanism of porous carbon materials, which requires a change from conventional thinking when choosing appropriate electrolytes. Here we show how simply changing the solvent of an electrolyte system can drastically influence the pseudocapacitive charge storage of the two-dimensional titanium carbide, Ti3C2 (a representative member of the MXene family). Measurements of the charge stored by Ti3C2 in lithium-containing electrolytes with nitrile-, carbonate- and sulfoxide-based solvents show that the use of a carbonate solvent doubles the charge stored by Ti3C2 when compared with the other solvent systems. We find that the chemical nature of the electrolyte solvent has a profound effect on the arrangement of molecules/ions in Ti3C2, which correlates directly to the total charge being stored. Having nearly completely desolvated lithium ions in Ti3C2 for the carbonate-based electrolyte leads to high volumetric capacitance at high charge–discharge rates, demonstrating the importance of considering all aspects of an electrochemical system during development. Effects from electrolytes on supercapacitor electrodes, especially pseudocapacitive materials, are important but often overlooked. Gogotsi and colleagues demonstrate strong influences from electrolyte solvents on charge-storage processes in a titanium carbide and identify a best-performing electrode/electrolyte couple for supercapacitors.