To improve the structural design of electrodes and interlayers for practical applications of Li–S batteries, we report two scalable porous CNT@C membranes for high-energy Li–S batteries. The asymmetric CNT@C (1:2) membrane with both dense and macroporous layers can act as an Al-free cathode for current collection and high sulfur loading, while the symmetric CNT@C (1:1) membrane with hierarchically porous networks can be used as an interlayer to trap lithium polysulfides (LiPSs), thus weakening the shuttle effect by strong adsorption of the N atoms toward LiPSs. The doped N sites in carbon membranes are identified as bifunctional active centers that electrocatalytically accelerate the oxidation of Li2S and polysulfide conversion. First-principles calculations reveal that the pyridinic and pyrrolic N sites exhibit favorable reactivity for strong adsorption/dissociation of polysulfide species. They lead to greatly reduced energy and kinetic barrier for polysulfide conversion without weakening the polysulfide adsorption on the membrane. Using the synergistic circulation groove with the two membranes, the practical S loading can be tailored from 1.2 to 6.1 mg cm–2. The Li–S battery can deliver an areal capacity of 4.6 mA h cm–2 (684 mA h g–1) at 0.2 C even at an ultrahigh S loading of 6.1 mg cm–2 and a lean electrolyte to sulfur ratio of 5.3 μL mg–1. Our work for scalable membrane fabrication and structural design provides a promising strategy for practical applications of high-energy Li–S batteries.
Lithium−sulfur batteries are regarded as one of the most promising candidates for next-generation energy storage systems because of their high energy density and the low cost of sulfur. However, practical applications are still impeded by sluggish redox kinetics and the shuttling effect of soluble intermediate lithium polysulfides (LiPSs), which induces irreversible loss of active materials, self-discharge, and thus poor cycle stability. Herein, a polysulfide-anchored catalytic polymer is reported to solve the shuttling behavior and improve battery performance. Natural polymer xanthan gum and konjac gum with abundant polar oxygen-containing functional groups (−OH, CO, −COOH, and −O−) that induce strong binding interactions with lithium polysulfide and reduce the energy barrier of the reaction from S 8 to Li 2 S are entangled with a conductive carbon nanotube (CNT) skeleton as a polysulfide shielding interlayer. Combined with the highly conductive CNT porous network that facilitates Li + ion transportation, the CNT−biomass gel interlayer is endowed with great capability of adsorbing and catalyzing the active sulfur. Benefiting from these synergistic attributes, the as-obtained CNT−biomass gel composite interlayer can achieve excellent performance of a high initial capacity of 998.2 mA h g −1 at 0.2C and a slight capacity decay of 0.078% per cycle at 0.5C over 200 cycles. More importantly, the battery demonstrates a cycle stability at a high sulfur loading of 3.0 mg cm −2 . The proposed strategy will contribute to the design of biomass-derived materials for Li−S batteries. Natural polymer xanthan gum and konjac gum with abundant polar oxygen-containing functional groups that induce strong binding interactions with lithium polysulfide and reduce the energy barrier of the reaction from S 8 to Li 2 S are entangled with a conductive carbon nanotube skeleton as a polysulfide shielding interlayer. The CNT−biomass gel interlayer is endowed with a great capability of adsorbing and catalyzing the active sulfur.
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