Rapid Gas-Engineering to the Manufacture of Graphene-Like Mesoporous Carbon Nanosheets with a Large Aspect Ratio.

Porous carbon nanosheets (PCNs) with a large two-dimensional morphology and high porosity have emerged as an important class of 2D materials, while developing novel technology to manufacture high-quality PCNs in terms of convenience, high output, and economic benefit remains a challenge. Herein, a rapid gas-engineering technology is developed to fabricate graphene-like mesoporous carbon nanosheets (MCNs) with large aspect ratios (>2500, length/thickness). By easy carbonization of calcium gluconate under reduced pressure, MCNs with ultrathin (∼12 nm) thickness, ultralarge (>20 µm) lamella morphology, and high surface area (∼1155 m2/g) are fabricated in kilogram scale. Two-dimensional lamella morphology transformation, pore architectures, and calcium compounds transformation mechanisms are unraveled by in situ variable temperature X-ray diffraction (VT-XRD), high-resolution transmission electron microscopy (HRTEM), ex situ scanning electron microscopy (SEM), and atomic force microscopy (AFM). The key to the synthesis is the negative pressure operation, which triggers the rapid gas expansion in a gas-solid system. This design relied on the gas expansion mechanism has realized producing of high-quality MCNs via a rapid, high-throughput, and cost-effective way. Due to high surface utilization and low weight density, when served as a lightweight separator coating layer, MCNs exhibit impressive capture ability toward polysulfides and achieve a high-stability lithium-sulfur battery.

Colloidal dispersion of Nb2O5/reduced graphene oxide nanocomposites as functional coating layer for polysulfide shuttle suppression and lithium anode protection of Li-S battery.

Functional separator, which bridges anode, electrolyte and cathode together, has the potential to offer a good solution for efficient polysulfide diffusion inhibition and anode protection of Li-S battery. Herein, a novel ultra-thin multifunctional separator is prepared by a facile coating of colloidal dispersion of Nb2O5/reduced graphene oxide nanocomposites (rGO) onto porous polypropylene (PP) matrix. Benefiting from the physical blocking effect of rGO layer and chemisorption of Nb2O5, the shuttle of polysulfides has been greatly suppressed. Meanwhile, the rGO layer functioning as a conductive upper current collector can improve the sulfur utilization, while the Nb2O5 with high activity promotes the transformation of sulfur-containing species. With the assistant of Nb2O5-rGO function layer, the sulfur cathode shows significantly improved electrochemical performance with a high specific capacity of 1328 mAh g-1 at 0.2C and 754 mAh g-1 retained after 200 cycles. The sulfur cathode also exhibits excellent rate capability and stable Coulombic efficiency of 91% without the addition of LiNO3 in the electrolyte. Moreover, the presence of thin Nb2O5-rGO layer also prevents the lithium surface corrosion and the dendrite growth in the lithium anode.