Functional Carbons Remedy the Shuttling of Polysulfides in Lithium–Sulfur Batteries: Confining, Trapping, Blocking, and Breaking up

Abstract

Carbon materials are usually used as the sulfur host in rechargeable lithiumsulfur (Li-S) batteries that are considered as promising electrochemical energy storage systems. However, the "shuttling" caused by the soluble lithium polysulfides (LiPSs) formed by the reaction of Li and sulfur causes rapid capacity fade and low sulfur utilization, greatly hindering their practical use. The carbon materials can also be tailored to prevent LiPS shuttling because of their abundant porosity and controllable surface chemical properties, which are divided into four specific functions: confining, trapping, blocking, and breaking up. Confinement means physically confining the LiPSs in pores in the carbon while trapping refers to chemical adsorption on the carbon surface to restrict their diffusion and promote their transformation to insoluble Li 2 S 2 /Li 2 S. Blocking means placing a barrier in the cells to inhibit LiPS diffusion to the anode, while breaking up means decreasing the size of the sulfur moiety to increase its affinity with carbons. The advantages and disadvantages of functional carbons in relation to these four functions are summarized and the specific ways to achieve them are highlighted. The design of advanced carbons with synergistic functions is discussed and some perspectives on the future development of carbons in Li-S batteries are given.

Sulfiphilic Few‐Layered MoSe2 Nanoflakes Decorated rGO as a Highly Efficient Sulfur Host for Lithium‐Sulfur Batteries

“…By contrast, the rGO/S just offers the discharge capacities of 527 and 458 mAh g −1 after 200 and 230 cycles at 1 C and 2 C, respectively, showing the poor capacity retention ability of the rGO/S. [37] At higher rates, the higher electric field force can offset the concentration gradient, buffering the migration of polysulfides to the anode. The initial discharge capacity reaches 1608 mAh g −1 , which is close to the theoretical capacity of 1675 mAh g −1 with the initial CE of about 98.9%.…”

“…[32,34] Carbides like TiC were embedded in the mesopores of CMK-3 in the presence of supercritical fluid. [37] CoSe 2 was reported to modify the separator and form a triple-phase electrolyte/CoSe 2 /graphene interface, favorably enhancing the kinetic behaviors of lithium polysulfides and regulating the uniform nucleation of Li 2 S. [38] Considering the exciting investigation, we chose the MoSe 2 as the polar material to further examine the applicability and workability of metal selenides to LSBs. [37] CoSe 2 was reported to modify the separator and form a triple-phase electrolyte/CoSe 2 /graphene interface, favorably enhancing the kinetic behaviors of lithium polysulfides and regulating the uniform nucleation of Li 2 S. [38] Considering the exciting investigation, we chose the MoSe 2 as the polar material to further examine the applicability and workability of metal selenides to LSBs.…”

Rational Fabrication of Nitrogen and Sulfur Codoped Carbon Nanotubes/MoS2 for High‐Performance Lithium–Sulfur Batteries

“…The primary strategy is to couple sulfur with appropriate anchors or hosts. A series of carbonaceous materials, such as hierarchical macro‐, meso‐, and microporous carbon, carbon spheres, and nanotubes, have usually been employed in the design of the structure of materials used in Li–S batteries . These carbon matrices can physically trap polysulfides in their pore structures and provide rapid pathways and a conductive framework for ion/electron (Li + /e − ) transport to improve the utilization of sulfur .…”

“…As eries of carbonaceous materials, such as hierarchical macro-, meso-, and microporous carbon,c arbon spheres, and nanotubes, have usually been employed in the design of the structure of materials used in Li-S batteries. [7][8][9] These carbon matrices can physically trap polysulfides in their pore structures and provide rapid pathways and ac onductive framework for ion/electron (Li + /e À )t ransport to improve the utilization of sulfur. [10] Unfortunately,t he inherently nonpolar carbon materials provide weak van der Waals adsorption to polar LiPSs, which cannot suppresst he diffusion of LiPSs during long-term cycling, inevitably causing rapid capacity decay.…”

Intertwined Nitrogen‐Doped Carbon Nanotube Microsphere as Polysulfide Grappler for High‐Performance Lithium‐Sulfur Batteries

“…There is only a low binding energy between them. [26,27] The roles can be summarized as the following four aspects: First, when the sulfur is combined with the carbon support material, the introduction of polar functional groups can promote the uniform penetration of sulfur into the pores of the carbon material, [28,29] which can prevent agglomeration, enhance the utilization of the active material of the positive electrode and thus increase the cycle stability; Secondly, during the discharge process, the N-containing functional groups can modify the carbonÀ sulfur interface, thereby stabilizing the electrochemical process of charging and discharging of LiÀ S batteries, and further enhancing the large-rate discharge capacity of LiÀ S batteries; [30] Third, regardless of whether Li 2 S or Li 2 S 2 is the final product of high polarity discharge, the intermediate Li 2 S x (4 � x � 8) is discharged, with the non-polar carbon skeletons, the introduced polar functional groups all have strong enough bonding forces to form bonds with them. Therefore, heteroatom doping or anchoring certain polar functional groups on the carbon surface can effectively improve the binding energy of carbon and sulfur.…”