Superhierarchical Cobalt‐Embedded Nitrogen‐Doped Porous Carbon Nanosheets as Two‐in‐One Hosts for High‐Performance Lithium–Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries, based on the redox reaction between elemental sulfur and lithium metal, have attracted great interest because of their inherently high theoretical energy density. However, the severe polysulfide shuttle effect and sluggish reaction kinetics in sulfur cathodes, as well as dendrite growth in lithium-metal anodes are great obstacles for their practical application. Herein, a two-in-one approach with superhierarchical cobalt-embedded nitrogen-doped porous carbon nanosheets (Co/N-PCNSs) as stable hosts for both elemental sulfur and metallic lithium to improve their performance simultaneously is reported. Experimental and theoretical results reveal that stable Co nanoparticles, elaborately encapsulated by N-doped graphitic carbon, can work synergistically with N heteroatoms to reserve the soluble polysulfides and promote the redox reaction kinetics of sulfur cathodes. Moreover, the high-surface-area pore structure and the Co-enhanced lithiophilic N heteroatoms in Co/N-PCNSs can regulate metallic lithium plating and successfully suppress lithium dendrite growth in the anodes. As a result, a full lithium-sulfur cell constructed with Co/N-PCNSs as two-in-one hosts demonstrates excellent capacity retention with stable Coulombic efficiency.

Expediting redox kinetics of sulfur species by atomic‐scale electrocatalysts in lithium–sulfur batteries

“…Powering the rapid LiPS conversion is critically important to realize high‐capacity, fast‐charge, and long‐term Li–S batteries. Based on these considerations, various electrocatalysts are applied in a working Li–S battery . However, most of them suffer from low surface‐to‐volume ratio, considerably sacrificing the electrocatalytic activities.…”

Separator Modified by Cobalt‐Embedded Carbon Nanosheets Enabling Chemisorption and Catalytic Effects of Polysulfides for High‐Energy‐Density Lithium‐Sulfur Batteries

“…[16,17] However, the modifications of these separators mainly focus on blocking polysulfides migration through electrostatic repulsion and/or physical/chemical interaction, the intercepted polysulfides could accumulate on the surface of the modified separator. [27] The NPCencapsulated metal nanoparticles (NPs) have been extensively employed as sulfur host materials in Li-S batteries [26,28] and as nanocatalysts in heterogeneous catalysis, [29] but their application as the separator modifiers has not been reported to date. These issues could lead to a relatively limited effect on improving the batteries performance.…”

Improving Polysulfides Adsorption and Redox Kinetics by the Co4N Nanoparticle/N‐Doped Carbon Composites for Lithium‐Sulfur Batteries

“…In addition, the synergistic effect between Co and doped N also existed in MOF‐Co, which has been verified by XPS results (Figure S5, Supporting Information). Co 2p in MOF‐Co has an ≈2 eV of blueshift with respect to bulk Co, which can strengthen the adsorption to LPSs . SEM of MOF‐Co 4 N at full discharge state was also tested (Figure b), which shows that, to a large extent, the morphology of MOF‐Co 4 N remained.…”

“…Compared to these three samples, MOF‐Co 4 N shows the best cycling performance, which is attributed to the strong LiPS anchoring capability of Co 4 N that effectively reduces the shuttle effect in the long‐term discharge/charge process and the proper catalyst effect of Co 4 N on the redox of polysulfides. Co are able to catalyze the polysulfides conversion, which can explain the better performance is achieved by MOF‐Co compared to MOF‐C . The electrochemical tests of MOF‐Co 4 N, MOF‐Co, and MOF‐C with blank electrolyte (without Li 2 S 6 ) were also tested as shown in Figure S6 (Supporting Information).…”