Advanced Sulfur Cathode Enabled by Highly Crumpled Nitrogen-Doped Graphene Sheets for High-Energy-Density Lithium–Sulfur Batteries

Abstract

Herein, we report a synthesis of highly crumpled nitrogen-doped graphene sheets with ultrahigh pore volume (5.4 cm(3)/g) via a simple thermally induced expansion strategy in absence of any templates. The wrinkled graphene sheets are interwoven rather than stacked, enabling rich nitrogen-containing active sites. Benefiting from the unique pore structure and nitrogen-doping induced strong polysulfide adsorption ability, lithium-sulfur battery cells using these wrinkled graphene sheets as both sulfur host and interlayer achieved a high capacity of ∼1000 mAh/g and exceptional cycling stability even at high sulfur content (≥80 wt %) and sulfur loading (5 mg sulfur/cm(2)). The high specific capacity together with the high sulfur loading push the areal capacity of sulfur cathodes to ∼5 mAh/cm(2), which is outstanding compared to other recently developed sulfur cathodes and ideal for practical applications.

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

“…As shown in Table S1, the molar ratio of C to N in CNB was 0.748, which was smaller than 0.764 for CÀCNN, and obviously the increased carbon was from the carbon doping. The high 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 nitrogen content of 56.7 at % was more than 10-fold larger than that of most N-doped carbon materials reported in literature, [22,32] and such a high nitrogen percentage is crucial for chemical adsorption of polysulfides.…”

“…For example, nitrogendoped carbon can chemically trap lithium polysulfides by the introduced nitrogen active sites. [19,20] However, even though the doping procedure is generally complex, there is a threshold for the nitrogen doping content (14.5 at %), [18,21] and the content is practically no more than 10 %, [5,22] which restricts the amount of active sites for polysulfides adsorption. Although other polar hosts like metal oxides (TiO 2 , MnO 2 , et al) have also been investigated to adsorb polysulfides by chemically interaction, [23][24][25] metal oxides have larger density than carbon materials and their derivatives, which increases inactive material fraction in the cell and decreases energy density of the full cell.…”

Structural Design of Lithium–Sulfur Batteries: From Fundamental Research to Practical Application

“…The design of multi-architectural and multi-functional cathode materials has the potential to overcome these challenges and has been one of the most researched strategies in recent years. Currently, physical routes including capillary force absorption [14,[51][52][53][54][55][56][57], shell coating [58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75], and chemical routes containing heteroatom-doped carbons [76][77][78][79][80][81][82][83][84][85][86][87][88][89][90] and metal-based additives [91][92][93][94][95][96][97][98][99]…”

Engineering Graphenes from the Nano- to the Macroscale for Electrochemical Energy Storage

“…Doping is recognized as an effective method to adjust the electronic conduction of graphene nanosheets, such as improving the conductivity and surface wettability, tuning the band gap, and changing the electron distribution [25][26][27]. Wu et al proposed nitrogen and boron doping to increase the electrical conductivity and electrochemical activity of graphenes.…”

“…Song et al fabricated highly crumpled graphene sheets with a large number of nitrogen-containing active sites and a large pore volume through a simple template-free and thermal expansion approach using cyanamide as both the nitrogen source and pore former. This highly crumpled nitrogendoped graphene acts as a porous and polar carbon host in a lithium-sulfur battery cathode to strongly confine the dissolution of soluble polysulfides intermediates, giving a specific capacity of 1000 mAh g −1 with both a high sulfur content and sulfur mass loading [27]. Chemical activation of graphene nanosheets is widely used to improve the specific surface area and tailor the pore structure of graphene-derived carbons for specific applications.…”