Electrochemical performance matching between LiTFSI/2-oxazolidinone complex electrolyte and various carbon materials with different pore sizes and surface areas

Electrochemical double layer capacitors(EDLCs) composed of various carbon electrodes with different pore sizes and surface areas[carbon nanotubes, mesoporous activated carbons(MEACs) and microporous activated carbons] and ionic liquids based on lithium bis(trifluoromethane sulfone) imide (LiTFSI) with 2-oxazolidinone(OZO) as the electrolyte were studied. Electrochemical performances were evaluated with quantum chemistry calculations, cyclic voltammetry and galvanostatic charge-discharge tests. The LiTFSI-OZO system exhibits superior physicochemical properties, such as a wide liquid-phase range and high ionic conductivity. The configurations of ions("free" ions, contact ion pairs and aggregates) in the electrolyte and their interactions have an important influence on the electrochemical performance of the LiTFSI-OZO system. The EDLCs containing MEACs, which have the largest surface area and most compatible pore size of the carbon materials, possesses the highest specific capacitance of 184.6 F/g. This work shows that it is necessary to closely match the pore sizes of electrode materials with the ion sizes of the electrolyte system to optimize the performance of novel room temperature ionic liquids.