Nitrogen‐Deficient Graphitic Carbon Nitride/Carbon Nanotube as Polysulfide Barrier of High‐Performance Lithium‐Sulfur Batteries

Abstract

Lithium‐sulfur (Li−S) batteries have been attracting growing interest in the past few years due to their outstanding theoretical energy density, but the lower cycle performance and especially the migration of polysulfides significantly inhibited its applicability. Herein, we propose a novel strategy for trapping lithium polysulfides (LiPSs) by combining nitrogen‐deficient graphitic carbon nitride (g‐C3N4–x) and carbon nanotubes (CNTs) to form a functional interlayer between the separator and sulfur cathode in Li−S batteries. The defect chemistry present in g‐C3N4–x not only improves the chemical affinity toward polysulfides but also catalyzes the polysulfide reactions. Besides, the interwoven scaffold‐like CNT network in the g‐C3N4–x/CNT composite accelerates the process of electron transfer. Based on this synergistic effect, the cells with g‐C3N4–x/CNT‐modified separators showed a remarkable discharge capacity of 1128 mAh g−1 at 0.2 C, and a reversible capacity of 774 mAh g−1 after 100 cycles, indicating an efficient strategy toward high‐performance modified separators.

Polypyrrole/Graphene Composite Interlayer: High Redox Kinetics of Polysulfides and Electrochemical Performance of Lithium–Sulfur Batteries Enabled by Unique Pyrrolic Nitrogen Sites

“…However, non-polar carbon nanomaterials show weak chemical affinity to PSs and poor electrolyte wettability, and drive slow lithium-ion transfer and redox kinetics of PSs, thus the electrochemical performance, especially the rate capability and the cycling performance of the LiÀ S batteries remains unsatisfactory. [19] Therefore, carbon materials are generally modified by doping hetero-atoms and polymer, [17,18,[20][21][22][23][24] which enhance the adsorption of PSs, the electronic conductivity of carbon matrix and the redox kinetics of sulfur species.…”

“…Carbonaceous materials are the most commonly reported separator modifiers for Li−S batteries, [14–18] which could effectually alleviate the shuttle effect of PSs by physical isolation and strong chemical adsorption of PSs owing to their large surface area. However, non‐polar carbon nanomaterials show weak chemical affinity to PSs and poor electrolyte wettability, and drive slow lithium‐ion transfer and redox kinetics of PSs, thus the electrochemical performance, especially the rate capability and the cycling performance of the Li−S batteries remains unsatisfactory [19] . Therefore, carbon materials are generally modified by doping hetero‐atoms and polymer, [17,18,20–24] which enhance the adsorption of PSs, the electronic conductivity of carbon matrix and the redox kinetics of sulfur species.…”

Carbon-Nitride-Based Materials for Advanced Lithium–Sulfur Batteries

“…Therefore, the Li–S cell with sCN modified separator delivered a high initial capacity of 637 mAh g −1 at 5C and a low capacity fading rate of 0.05% per cycle after 500 cycles. Besides, various g-C 3 N 4 materials with different defect structures, concentrations, and preparation methods have been reported, which obviously improve the performance of Li–S batteries [ 78 , 79 ]. However, excessive N defects could destroy the structure of g-C 3 N 4 and thus decrease its electron transport and LiPSs adsorption capability.…”

Bidirectional Catalyst with Robust Lithiophilicity and Sulfiphilicity for Advanced Lithium–Sulfur Battery

“…Owing to its high content of CN heteroatom moieties and improved electric conductivity, nitrogen‐deficient rich graphite carbon nitride (ND‐ g ‐C 3 N 4 , denoted as CN) is already employed in lithium–sulfur battery for a while which can enhance the affinity to LiPSs through dipolar‐dipolar bonding and accelerate the sulfur redox kinetics to certain extent. [ 19 ] Nevertheless, according to our previous research, [ 20 ] the bonds form between g ‐C 3 N 4 and LiPS are assumed to be NLiS bridging configuration, which may lead to slightly less capture ability to LiPS and poor catalytic/conversion effect. Generally, the CN is prepared by a facile magnesiothermic reduction process between magnesium and g ‐C 3 N 4 , and the by‐product is simply considered to be Mg 3 N 2 , [ 21 ] and it is usually ignored.…”