A dual utilization strategy of lignosulfonate for MXene asymmetric supercapacitor with high area energy density

Two-dimensional transition metal carbides (MXenes) have shown extraordinary potential in energy storage device, especially in supercapacitors. However, the major drawbacks of these eletrode materials are the re-stacking problem and the narrow operating potential range, which limit them to reach high energy density. The P-π conjugate structure of lignosulfonate (LS) endows α and β carbon a strong chemical reactivity and local positive potential, which can modify the surface of MXene and avoid the re-stacking problem. Herein, for the first time, the LS modified-MXene (Ti3C2Tx)-reduced graphene oxide (rGO) 3D porous (MLSG) aerogel is synthesized. The MLSG-6 aerogel exhibits more excellent electrochemical performance when compared to pure MXene even with the high mass-loading of 5.1 mg cm−2. As a supercapacitor electrode, the MLSG-6 aerogel exhibits high specific capacitance of 386F g−1 and 1967 mF cm−2 at scan of 2 mV s−1, and excellent rate performance with the capacitance of 241F g−1 at scan of 100 mV s−1. Moreover, utilizing redox pseudocapacitive characteristics of LS under positive potential, the 3D porous LS-functionalized reduced graphene oxide (LSG) aerogel is reported to match with MLSG aerogel to construct an all-pseudocapacitive asymmetric supercapacitor with potential range of 1.45 V. Consequently, the asymmetric supercapacitor can deliver an energy density of 142 µW h cm−2 at power density of 4900 μW cm−2, with 96.3% capacitance retention after 10,000 charge–discharge cycles. This work realizes the dual utilization of high chemical reactivity and pseudocapacitance characteristics of LS to the negative and positive electrodes of the asymmetric supercapacitor.