The Role of Alkali Cation Intercalates on the Electrochemical Characteristics of Nb<sub>2</sub>CT<sub><i>X</i></sub> MXene for Energy Storage
Liping Liao, Bing Wu, Evgeniya Kovalska, Vlastimil Mazánek, Martin Veselý, Ivo Marek, Lucie Spejchalová, Zdeněk Sofer
Abstract
Abstract 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 Nb 2 CT x 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 Li 2 SO 4 , Na 2 SO 4 , and K 2 SO 4 electrolytes with d‐spacing. Additionally, our results showed that the Nb 2 CT x electrode exhibited higher electrochemical performance in the presence of Li 2 SO 4 than in that of Na 2 SO 4 and K 2 SO 4 . This is partly because the smaller‐sized Li + transports quickly and intercalates between the layers of Nb 2 CT x easily. Poor ion transport in the Na 2 SO 4 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 Nb 2 CT x electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes.