Exfoliated MoS₂ Nanosheet/Cellulose Nanocrystal Flexible Composite Films as Electrodes for Zinc Batteries

The study presents a more efficient way of exfoliating MoS₂ in water and the exfoliated MoS₂ was used in an electrode. The electrodes were prepared from exfoliated MoS₂ (active material)–nanocrystalline cellulose (binder) with carbon nanotubes (electron-conducting support) and demonstrated in a zinc battery half-cell that showed a Coulombic efficiency of 90%. Successful exfoliation of MoS₂ was done by sonication of bulk MoS₂ with sulfated cellulose nanocrystals (CNC) for 4 h. The exfoliation was confirmed by Raman and transmission electron microscopy; interestingly, the Raman signals for exfoliated MoS₂ show a blue shift for both A_1g and E_2g¹ bands, which may be an indication of an induced lattice strain effect from the CNC on MoS₂. The resulting stable water suspension showed no tendency of precipitation after 2 months of standing. The zeta potential, ζ, for sodium sulfated CNC (CNC–OSO₃Na)–MoS₂ in water suspension was −45 mV, whereas sulfated CNC (CNC–OSO₃H)–MoS₂ in water suspension had a zeta potential of −35 mV. The sodium form of sulfated CNCs displayed micelle characteristics, similar to sodium dodecyl sulfate (SDS), with a critical aggregation concentration (CAC) of 1.1 wt %. At CAC, the CNCs efficiently exfoliated MoS₂, which is at a much lower concentration than has been reported for synthetic surfactants like SDS and cetyl trimethyl ammonium bromide.