Approaching the theoretical sodium storage capacity and ultrahigh rate of layer-expanded MoS${}_2$ by interfacial engineering on N-doped graphene

Molybdenum disulfide (MoS${}_2$) holds great potential for sodium storage due to its high theoretical capacity of 670 mAh g${}^{-1}$. However, its theoretical capacity is hardly realized because of low conductivity, sluggish electrochemical kinetics, and unsatisfied structural stability. Herein, a polyaniline-mediated interfacial engineering strategy for the growth of interlayer-expanded MoS${}_2$ nanoflowers on N-doped graphene "land" (E-MoS${}_2$/NG) using Mo${}_7$O${}_{24}$${}^{6-}$ anions adsorbed on positively charged polyaniline as the "seeds" is reported. The strong interfacial interaction between MoS${}_2$ and graphene through Mo - N bonds as well as ultrathin interlayer-expanded MoS${}_2$ can significantly improve the electrochemical kinetics and structural stability. As a result, E-MoS${}_2$/NG with a high MoS${}_2$ content of 90 wt% shows a high capacity (620 mAh g${}^{-1}$ at 0.1 A g${}^{-1}$), an ultrahigh rate capability (201 mAh g${}^{-1}$ at 50 A g${}^{-1}$), and outstanding cycle performance (390 mAh g${}^{-1}$ after 1000 cycles at 1 A g${}^{-1}$). Importantly, MoS${}_2$ in the composite approaches its theoretical capacity of 670 mAh g${}^{-1}$. Furthermore, the assembled E-MoS${}_2$/NG//activated carbon sodium ion capacitor delivers high energy densities of 150 and 82 Wh kg${}^{-1}$ at 35 and 14 421 W kg${}^{-1}$, respectively, and a capacity retention of 78.1% after 1500 cycles at 10 A g${}^{-1}$, demonstrating great potential for practical application. (© 2021 Wiley-VCH GmbH)