Catalytic Effects in Lithium–Sulfur Batteries: Promoted Sulfur Transformation and Reduced Shuttle Effect

172

109

Lithium‐sulfur (Li‐S) batteries are considered to be one of the promising next‐generation energy storage systems. Considerable progress has been achieved in sulfur composite cathodes, but high cycling stability and discharging capacity at the expense of volumetric capacity have offset their advantages. Herein, a functional separator is presented by coating cobalt‐embedded nitrogen‐doped porous carbon nanosheets and graphene on one surface of a commercial polypropylene separator. The coating layer not only suppresses the polysulfide shuttle effect through chemical affinity, but also functions as an electrocatalyst to propel catalytic conversion of intercepted polysulfides. The slurry‐bladed carbon nanotubes/sulfur cathode with 90 wt% sulfur deliver high reversible capacity of 1103 mA h g−1 and volumetric capacity of 1062 mA h cm−3 at 0.2 C, and the freestanding carbon nanofibers/sulfur cathode provides a high discharging capacity of 1190 mA h g−1 and volumetric capacity of 1136 mA h cm−3 at high sulfur content of 78 wt% and sulfur loading of 10.5 mg cm−2. The electrochemical performance is comparable with or even superior to those in the state‐of‐the‐art carbon‐based sulfur cathodes. The separator reported in this work holds great promise for the development of high‐energy‐density Li‐S batteries.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Cheng

Pan

Chen

et al. 2019

172

109

“…In the process of repeated discharge and charge, lithium ions are prone to form uneven deposition on the surface of lithium metal, which generates lithium dendrites and affects the safety and cyclic stability of devices. [9][10][11] To address this problem, scientists have focused on studying physical blocking and chemical adsorption of the LiPSs in the past years. [6][7][8] However, the long-chain LiPSs are soluble, which can dissolve into the electrolyte and inhibit the reaction kinetics, causing the low utilization of active sulfur and inferior cycling stability.…”

mentioning

confidence: 99%

Adsorption‐Catalysis Design in the Lithium‐Sulfur Battery

Zhang

Chen

Xue

et al. 2019

312

247

Lithium‐sulfur (Li‐S) batteries are one of the most promising next‐generation energy‐storage systems. Nevertheless, the sluggish sulfur redox and shuttle effect in Li‐S batteries are the major obstacles to their commercial application. Previous investigations on adsorption for LiPSs have made great progress but cannot restrain the shuttle effect. Catalysts can enhance the reaction kinetics, and then alleviate the shuttle effect. The synergistic relationship between adsorption and catalysis has become the hotspot for research into suppressing the shuttle effect and improving battery performance. Herein, the adsorption‐catalysis synergy in Li‐S batteries is reviewed, the adsorption‐catalysis designs are divided into four categories: adsorption‐catalysis for LiPSs aggregation, polythionate or thiosulfate generation, and sulfur radical formation, as well as other adsorption‐catalysis. Then advanced strategies, future perspectives, and challenges are proposed to aim at long‐life and high‐efficiency Li‐S batteries.

“…The dissolved polysulfides tend to migrate from the cathode to the anode side, causing unwanted parasitic reactions with lithium-metal anode and active-material loss from the sulfur cathode. [21][22][23] Thus, numerous efforts have been focused on the chemical restriction for polysulfides to further improve the electrochemical functionality. [3] Additionally, the degradation of anode and volume changes of sulfur species during reaction also undermine the electrochemical stability and cycle life of Li-S batteries, challenging the practical use of Li-S technology.…”

mentioning

confidence: 99%

Rational Design of a Dual‐Function Hybrid Cathode Substrate for Lithium–Sulfur Batteries

Liu

Chung

Manthiram

2018

105

of Li-S technology is still impeded by intrinsic material challenges. First, sulfur and its discharge product lithium sulfide are insulating in nature, which deteriorates the active-material utilization and leads to sluggish redox-reaction kinetics. [2] Second, during charge and discharge, polysulfide intermediates (Li 2 S x , 4 ≤ x ≤ 8) form and easily dissolve into the liquid electrolyte. The dissolved polysulfides tend to migrate from the cathode to the anode side, causing unwanted parasitic reactions with lithium-metal anode and active-material loss from the sulfur cathode. These drawbacks lead to an irreversible capacity fade and low Coulombic efficiency. [3] Additionally, the degradation of anode and volume changes of sulfur species during reaction also undermine the electrochemical stability and cycle life of Li-S batteries, challenging the practical use of Li-S technology. [4,5] Intensive studies have been devoted to addressing the aforementioned problems, including new cathode design, [6][7][8][9] functional interlayer/separator fabrication, [10][11][12] efficient anode protection, [13][14][15][16] and optimized electrolyte formulas. [17][18][19][20] In view of cathode modification, it has been demonstrated that nonpolar carbon matrix with only physical polysulfide confinement may not be enough for high-loading cell performance during long cycle life. [21][22][23] Thus, numerous efforts have been focused on the chemical restriction for polysulfides to further improve the electrochemical functionality. [4,23] Transition-metal compounds, including metal oxides, [24] sulfides, [21] nitrides, [25] and carbides, [26] have been proven as efficient polysulfide traps by offering chemical polysulfide-adsorption sites. Among them, metal sulfides attract particular interest due to their strong sulfiphilicity together with multiple thermodynamically stable crystal structures and stoichiometric compositions. [27] For instance, cobalt disulfide (CoS 2 ), [21] titanium disulfide (TiS 2 ), [28,29] and iron disulfide (FeS 2 ) [30] have been applied as sulfur hosts and have been demonstrated with a strong chemical interaction capability toward migrating polysulfides. [23] However, these metal sulfides mainly exist in the form of large particles with varying levels of agglomeration, greatly shrinking the surface area for polysulfide adsorption and limiting the amount of sulfur species that could be loaded. [27] Accordingly, the sulfur cathodes used in most metal sulfide-related reports have an insignificant sulfur content of less than 60 wt% and a low sulfur A unique 3D hybrid sponge with chemically coupled nickel disulfide-reduced graphene oxide (NiS 2 -RGO) framework is rationally developed as an effective polysulfide reservoir through a biomolecule-assisted self-assembly synthesis. An optimized amount of NiS 2 (≈18 wt%) with porous nanoflower-like morphology is uniformly in situ grown on the RGO substrate, providing abundant active sites to adsorb and localize polysulfides. The improved polysulfide adsorptivity from sul...