Lulu Ma

Sandwich-Type Nitrogen and Sulfur Codoped Graphene-Backboned Porous Carbon Coated Separator for High Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been identified as the greatest potential next- generation energy-storage systems because of the large theoretical energy density of 2600 Wh kg−1. However, its practical application on a massive scale is impeded by severe capacity loss resulted from the notorious polysulfides shuttle. Here, we first present a novel technique to synthesize sandwich-type nitrogen and sulfur codoped graphene-backboned porous carbon (NSGPC) to modify the commercial polypropylene separator in Li-S batteries. The as-synthesized NSGPC exhibits a unique micro/mesoporous carbon framework, large specific surface area (2439.0 m2 g−1), high pore volume (1.78 cm3 g−1), good conductivity, and in situ nitrogen (1.86 at %) and sulfur (5.26 at %) co-doping. Benefiting from the particular physical properties and chemical components of NSGPC, the resultant NSGPC-coated separator not only can facilitate rapid Li+ ions and electrons transfer, but also can restrict the dissolution of polysulfides to alleviate the shuttle effect by combining the physical absorption and strong chemical adsorption. As a result, Li-S batteries with NSGPC-coated separator exhibit high initial reversible capacity (1208.6 mAh g−1 at 0.2 C), excellent rate capability (596.6 mAh g−1 at 5 C), and superior cycling stability (over 500 cycles at 2 C with 0.074% capacity decay each cycle). Propelling our easy-designed pure sulfur cathode to a extremely increased mass loading of 3.4 mg cm−2 (70 wt. % sulfur), the Li-S batteries with this functional composite separator exhibit a superior high initial capacity of 1171.7 mAh g−1, which is quite beneficial to commercialized applications.

Wheat Straw-Derived N-, O-, and S-Tri-doped Porous Carbon with Ultrahigh Specific Surface Area for Lithium-Sulfur Batteries

Recently, lithium-sulfur (Li-S) batteries have been greeted by a huge ovation owing to their very high theoretical specific capacity (1675 mAh·g−1) and theoretical energy density (2600 Wh·kg−1). However, the full commercialization of Li-S batteries is still hindered by dramatic capacity fading resulting from the notorious “shuttle effect” of polysulfides. Herein, we first describe the development of a facile, inexpensive, and high-producing strategy for the fabrication of N-, O-, and S-tri-doped porous carbon (NOSPC) via pyrolysis of natural wheat straw, followed by KOH activation. The as-obtained NOSPC shows characteristic features of a highly porous carbon frame, ultrahigh specific surface area (3101.8 m2·g−1), large pore volume (1.92 cm3·g−1), good electrical conductivity, and in situ nitrogen (1.36 at %), oxygen (7.43 at %), and sulfur (0.7 at %) tri-doping. The NOSPC is afterwards selected to fabricate the NOSPC-sulfur (NOSPC/S) composite for the Li-S batteries cathode material. The as-prepared NOSPC/S cathode delivers a large initial discharge capacity (1049.2 mAh·g−1 at 0.2 C), good cycling stability (retains a reversible capacity of 454.7 mAh·g−1 over 500 cycles at 1 C with a low capacity decay of 0.088% per cycle), and superior rate performance (619.2 mAh·g−1 at 2 C). The excellent electrochemical performance is mainly attributed to the synergistic effects of structural restriction and multidimensional chemical adsorptions for cooperatively repressing the polysulfides shuttle.