Abstract
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.
Highlights
In recent years, lithium-sulfur (Li-S) batteries have been identified as the greatest potential next- generation energy-storage devices because of their large theoretical energy density (2600 Wh kg−1) and theoretical specific capacity (1675 mAh g−1)
The schematic illustration of Li-S cells with nitrogen and sulfur codoped graphene-backboned porous carbon (NSGPC)-coated separator is shown in Figure 1, where the NSGPC coating is faced toward the sulfur cathode, acting to restrain the migrating polysulfides through physical absorption and strong chemical adsorption, and serving as a conductive upper current collector to reutilize the intercepted active materials during the following cycles
Benefiting from the particular physical properties and chemical components of NSGPC, the as-synthesized NSGPC-coated separator for Li-S batteries can serve as an upper current collector to offer rapid Li+ ions and electrons transport pathways, and can restrict the dissolution of polysulfides to alleviate the shuttle effect by combining the physical absorption and strong chemical adsorption
Summary
Lithium-sulfur (Li-S) batteries have been identified as the greatest potential next- generation energy-storage devices because of their large theoretical energy density (2600 Wh kg−1) and theoretical specific capacity (1675 mAh g−1). Sulfur has some obvious advantages over current transition metals cathodes in lithium-ion batteries of natural abundance, inexpensive and eco-friendliness [1,2] Despite their appealing features, the practical application of Li-S batteries is still seriously impeded by several drawbacks, including: (i) the poor electrical conductivity of sulfur and its final discharge product Li2S/Li2S2, leading to sluggish electron transfer and low sulfur utilization; (ii) the severe volume expansion (~80%) caused by sulfur reduction to Li2S, resulting in capacity decaying and structural instability; and (iii) the dissolution and notorious “shuttle effect” of lithium polysulfides, giving rise to poor coulombic efficiency and inferior cycling life [3,4]. Strong chemical binding of lithium polysulfides to the carbon hosts is badly needed to improve polysulfides adsorption and, active material utilization and cycling life of Li-S batteries
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