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

Abstract

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.