Defective Graphitic Carbon Nitride Modified Separators with Efficient Polysulfide Traps and Catalytic Sites for Fast and Reliable Sulfur Electrochemistry

Abstract

The serious shuttle effect of lithium‐sulfur batteries limits the efficient realization of high rate charging and discharging under high sulfur loading in practical applications. Herein, this work reports a strong mitigation toward lithium polysulfide (LiPSs) adsorption/catalysis by introducing defective graphite phase carbon nitride (g‐C3N4) as an effective additive. Without significant weight increase, the nitrogen deficient g‐C3N4, in the form of ultrafine spindle‐like nitrogen deficient g‐C3N4−x (sCN), can be easily combined with commercial poly‐propylene (PP) separators after hydrophilic modification of polydopamine, which corresponds to an ultralow overall weightiness contribution of 0.17 mg cm−2. Physical/electrochemical characterizations and theoretical studies reveal that sCN exhibits strong electrostatic attraction with LiPSs by nitrogen defects and new formation of cyano groups near edges, thereby maintaining rapid and reliable LiS electrochemistry. Of particular importance is the chainmail catalyst design with separators that enable magic polysulfides adsorption effect and desirable thermostability/wettability, which guarantees the sCNPP‐assembled cells with long and stable durability over 500 cycles at 5.0 C (capacity fading rate: 0.05% per cycle), and a high capability of 476 mAh g−1 is obtained.

A Mott–Schottky Heterogeneous Layer for Li–S Batteries: Enabling Both High Stability and Commercial‐Sulfur Utilization

“…The fast catalytic conversion of intercepted LiPSs on Mott-Schottky RPM is investigated by CV curves of Li 2 S 6 symmetrical cells within a voltage window of −1.0 to 1.0 V. As shown in Figure S17, Supporting Information, RPM exhibits three reduction peaks at 0.09, −0.07, and −0.35 V, and three oxidation peaks at −0.09, 0.07, and 0.35 V, corresponding to the conversion of S 8 to Li 2 S 6 , and then to Li 2 S 4 , and finally to Li 2 S 2 /Li 2 S. [11] Specifically, RPM-based cell exhibits much higher peak current density and narrower peak separation than those of RGO-PANI and MoS 2 , demonstrating that RPM can efficiently accelerate the conversion rates of sulfur species due to the specific Motty-Schottky heterostructure. [63] Linear sweep voltammetry (LSV) measurements are carried out to study the kinetics of Li 2 S dissolution, where RPM enables a much smaller onset potential and stronger current response than RGO-PANI and MoS 2 (Figure 4f).…”

“…Modification of separators (including interlayers) in LSBs has been verified to be a simple and effective strategy to suppress the polysulfides' shuttle effect. [11] Since the carbon paper interlayer was first proposed by Manthiram et al, [12] carbon materials such as graphene, [13] carbon nanotubes, [14] carbon nanofibers, [15] and their hybrids, [16] have been widely investigated in separator modification. However, the shuttle effect and low sulfur utilization still exist during the long-term charge/discharge process because of the poor interfacial compatibility between nonpolar carbon and polar LiPSs.…”

A Heterostructured Sulfonated CNT/Sulfur/CNT Cathode for Promoting the Binary Conversion of Polysulfides in Lithium‐Metal Batteries

“…The curve of the M/S/M-SO 3 Li electrode displays three pairs of highly reversible redox peaks at À 0.01/0.01 V (reduction of S to Li 2 S 6 and oxidation of Li 2 S to Li 2 S 2 ), À 0.19/0.19 V (reduction of L 2 S 6 to Li 2 S 2 and oxidation of Li 2 S 6 to S) and À 0.44/0.44 V (reduction of Li 2 S 2 to Li 2 S and oxidation of Li 2 S 2 to Li 2 S 6 ). [63,64] For the M/S/M electrode, these peaks appear at À 0.04/0.03, À 0.24/0.24 and À 0.58/0.56 V, thereby confirming the considerable improvement in the electrode stability and the immobilization and utilization of sulfur species. Moreover, the M/S/M-SO 3 Li electrode exhibits a significantly higher peak current, sharper peaks and smaller polarization than that of the M/S/M electrode.…”

A spatially efficient “tube-in-tube” hybrid for durable sulfur electrochemistry

“…Polar materials (e.g., metal nanoparticles, 27 metal oxides, 28,29 metal suldes 30 ) have been demonstrated to have a considerable catalytic effect on sulfur conversion, which offers a promising strategy to address the shuttle and kinetic issues simultaneously. In this regard, defect engineering 31,32 is a powerful means to nely tune the electronic structure and polarity towards favorable physical/ chemical features for further catalyst optimization.…”