Polar Ultrathin Self‐Doping Carbon Nitride Nanosheets with Intrinsic Polysulfide Adsorption for High Performance Lithium‐Sulfur Batteries

Abstract

Lithium-sulfur (LiÀS) batteries are promising for next-generation electrochemical energy storage due to their high energy density and low cost. Here, we introduce light-weight polar carbon selfdoping C 3 N 4 nanosheets (CÀCNN) as sulfur host for the fabrication of high performance LiÀS batteries. The role of carbon doping in boosting the electrical conductivity of CÀCNN is revealed by electrochemical impedance spectroscopy and electrical conductivity measurements. The strong chemical interactions between CÀCNN and polysulfides are investigated by adsorption and post-mortem X-ray photoelectron spectroscopy analysis. Benefiting from the high surface area, enhanced electrical conductivity and high content of active N species (56.7 at %) in CÀCNN, the strong chemical interactions between CÀCNN and polysulfides can be fully exploited to minimize the shuttle effect and achieve long cycle life of LiÀS batteries. As a result, the CÀCNN/S cathode delivers a high specific capacity of 1050 mAh g À1 , good rate capability and excellent cycling stability with a low capacity decay of 0.07 % per cycle at 1 C over 500 cycles, showing better performance than nitrogendoped graphene. A performance comparison with the literature also shows that CÀCNN is one of the most promising nitrogencontaining carbon materials for long cycle life LiÀS batteries.

A Review of Heteroatom Doped Materials for Advanced Lithium–Sulfur Batteries

“…[ 11 ] Although the strategies of heteroatom doping and self‐doping can greatly promote the electronic conductivity of g‐C 3 N 4 , the conductivity is much lower than that of conductive carbon materials, which is insufficient to achieve high‐rate Li‐S batteries. [ 87,94 ] Therefore, the composite of g‐C 3 N 4 and conductive carbon materials may be a better choice to promote the conductivity. It is necessary to rationally design the ration of g‐C 3 N 4 and carbon, and optimize the interfacial contact within the composite.…”

“…Heteroatom doping can decrease the concentration of N atoms in CN and subsequently lead to the enhancement of electronic conductivity. Based on the above conclusion, Kuang's group [ 94 ] proposed the carbon self‐doping of CN to solve the demerits of original CN. Bulk g‐C 3 N 4 (BCN), and carbon doped bulk g‐C 3 N 4 (C‐BCN) were prepared through the one step pyrolysis and hydrothermal/pyrolysis method, respectively, and carbon‐doped g‐C 3 N 4 with nanosheet‐like structure (C‐NCN) was obtained by the sonication exfoliation of C‐BCN.…”

Two‐Dimensional Material‐Functionalized Separators for High‐Energy‐Density Metal–Sulfur and Metal‐Based Batteries

“…It is clear that modifying the separator with conductive graphene-based materials can form an interconnected network to guarantee the C-rate of insulative Sc athode. [25] Additionally, the barrier effect of the coating layers can suppress the migration of PSs, enhancing the stability of the LSBs. However,i t could fill the pores of the PP separator and cause short circuiting, raising the safety concern for practical application.…”

Hierarchically Designed CNF/S−Cu/CNF Nonwoven Electrode as Free‐Standing Cathode for Lithium−Sulfur Batteries

“…The parameters extracted from the related equivalent circuit are listed in Table S1. [13,29,40,[50][51][52][53][54][55][56][57][58] To further confirm the effective physical and chemical sulfur fixation of the sandwich structural CNF/SÀCu/CNF composite during the electrochemical cycling, the cycled batteries are dismantled. [48,49] The cycle performance of CNF/SÀCu/CNF and CNF/S/CNF film electrodes under a high current rate of 1 A g À1 is showed in Figure 5.…”

“…Apparently, the cell using functional fiber or self-standing carbon is more attractive in terms of high S utilization under same current density, which is favor for practical LiÀS batteries. [13,29,40,[50][51][52][53][54][55][56][57][58] To further confirm the effective physical and chemical sulfur fixation of the sandwich structural CNF/SÀCu/CNF composite during the electrochemical cycling, the cycled batteries are dismantled. The digital photos, SEM cross-section image and the correspongding elements EDS mapping of the CNF/SÀCu/ CNF electrodes after 300 charge-discharge cycles are presented in Figure S5.…”