Porous graphene-like MoS₂/carbon hierarchies for high-performance pseudocapacitive sodium storage

Layered MoS2 has been considered as a promising anode material for sodium-ion batteries (SIBs), but it suffers from low electric/ionic conductivity as well as severe volume variation upon ion insertion/extraction, which leads to poor electrochemical performance. To address this issue, we demonstrate a facile synthesis of graphene-like MoS2/carbon (denoted as MoS2/C) with porous hierarchical nanostructures, in which few-layered MoS2 with expanded (002) planes is successfully hybridized/doped with N,S-codoped carbon species, via a template-assisted nanocasting method. The simultaneous thermal decomposition of the Mo/S source (i.e., (NH4)2MoS4) and the N/C source (i.e., polyvinyl pyrrolidone, PVP) within the confined spaces constructed by the removable template (i.e., CaCO3) leads to the straightforward hybridization/doping of MoS2/C, and the carbon content can be readily controlled by adjusting the amount of PVP introduced, which greatly affects the sodium storage performance of the electrodes. After template removal, the as-prepared porous MoS2/C hierarchies constructed by graphene-like nanosheets display a large pore volume and highly exposed active surface, which efficiently enhance the electrical conductivity and the ion diffusivity. When evaluated as an anode material for SIBs, the optimized MoS2/C electrode demonstrates predominantly pseudocapacitive sodium storage behavior (with a high contribution of 89.9% at 1.2 mV s-1), delivering high reversible capacities of 397 mA h g-1 at 0.5 A g-1 after 300 cycles and 370 mA h g-1 at 1 A g-1 after 1000 cycles.