Multifunctional molecule-grafted V${}_2$C MXene as high-kinetics potassium-ion-intercalation anodes for dual-ion energy storage devices

Constructing dual-ion energy storage devices using anion-intercalation graphite cathodes offers the unique opportunity to simultaneously achieve high energy density and output power density. However, a critical challenge remains in the lack of proper anodes that match with graphite cathodes, particularly in sustainable electrolyte systems using abundant potassium. Here, a surface grafting approach utilizing multifunctional azobenzene sulfonic acid is reported, which transforms V${}_2$C MXene into a high-kinetics K${}^{+}$-intercalation anode (denoted ASA-V${}_2$C) for dual-ion energy storage devices. Importantly, the grafted azobenzene sulfonic acid offers extra K${}^{+}$-storage centers and fast K${}^{+}$-hopping sites, while concurrently acting as a buffer between V${}_2$C layers to mitigate the structural distortion during K${}^{+}$ intercalation/de-intercalation. These functionalities enable the V${}_2$C electrode with significantly enhanced specific capacity (173.9 mAh g${}^{-1}$ vs 121.5 mAh g${}^{-1}$ at 0.05 A g${}^{-1}$), rate capability (43.1% vs 12.0% at 20 A g${}^{-1}$), and cycling stability (80.3% vs 45.2% after 900 cycles at 0.05 A g${}^{-1}$). When coupled with an anion-intercalation graphite cathode, the ASA-V${}_2$C anode demonstrates its potential in a dual-ion energy storage device. Notably, the device depicts a maximum energy density of 175 Wh kg${}^{-1}$ and a supercapacitor-comparable power density of 6.5 kW kg${}^{-1}$, outperforming recently reported Li${}^{+}$-, Na${}^{+}$-, and K${}^{+}$-based dual-ion devices. (© 2023 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)