The Role of Alkali Cation Intercalates on the Electrochemical Characteristics of Nb2CTX MXene for Energy Storage

The intercalation of cations into layered‐structure electrode materials has long been studied in depth for energy storage applications. In particular, Li+‐, Na+‐, and K+‐based cation transport in energy storage devices such as batteries and electrochemical capacitors is closely related to the capacitance behavior. We have exploited different sizes of cations from aqueous salt electrolytes intercalating into a layered Nb2CTx electrode in a supercapacitor for the first time. As a result, we have demonstrated that capacitive performance was dependent on cation intercalation behavior. The interlayer spacing expansion of the electrode material can be observed in Li2SO4, Na2SO4, and K2SO4 electrolytes with d‐spacing. Additionally, our results showed that the Nb2CTx electrode exhibited higher electrochemical performance in the presence of Li2SO4 than in that of Na2SO4 and K2SO4. This is partly because the smaller‐sized Li+ transports quickly and intercalates between the layers of Nb2CTx easily. Poor ion transport in the Na2SO4 electrolyte limited the electrode capacitance and presented the lowest electrochemical performance, although the cation radius follows Li+>Na+>K+. Our experimental studies provide direct evidence for the intercalation mechanism of Li+, Na+, and K+ on the 2D layered Nb2CTx electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes. Different size cations from aqueous salt electrolyte intercalating into layered Nb2CTx electrode in supercapacitor were explored. The extent of interlayer expansion of electrode material varies with the size of the intercalation cations. Na+ ions showed the slowest permeation rate in the spacing between Nb2CTx layers compared to Li+ and K+.