Graphene‐Supported Nitrogen and Boron Rich Carbon Layer for Improved Performance of Lithium–Sulfur Batteries Due to Enhanced Chemisorption of Lithium Polysulfides

Abstract

the charge process, and this is considered to be another factor contributing to the rapid decay of Li-S batteries.Recently, it has been reported that nitrogen-doped carbon exhibits strong chemisorption for polysulfi des and Li 2 S, and consequently longer cycling performance has been achieved by developing N-doped carbon/S composites. [ 10 ] It has been demonstrated that the electronegative N atoms in the carbon matrix are particularly effective in forming S x Li⋅⋅⋅N interactions via the lone-pair electrons of N because of the strong interaction due to Lewis acid-base interaction between Li + cations in Li 2 S x and N atoms in the carbon matrix. [ 10 ] Alternatively, boron atoms, as an electron-defi cient alternative to N atoms, are electropositive in the carbon framework, thus leading to the chemisorption of polysulfi de anions (S x 2− ). [ 11 ] Accordingly, it was reported very recently that a boron-doped carbon host can also improve the performance of S composite cathodes. [ 11 ] As reviewed above, recent carbon host design strategies based on the enhanced chemisorption of lithium polysulfi de (Li 2 S x , 4 ≤ x ≤ 8) and Li 2 S rely solely on either the chemisorption of Li + cations in Li 2 S and lithium polysulfi des at negatively polarized N atoms or on the chemisorption of polysulfi des anion at positively polarized B atoms. If N atoms and B atoms are both introduced into the carbon, the chemical adsorption for both Li + cations and polysulfi des anions can be increased simultaneously, which may further enhance the cycling performance of the C/S composite cathode. We especially note that if the B atoms are adjacent to the N atoms to form an N = B/N-B structure in the carbon framework, the polarization of both B atoms and N atoms will be further enhanced because the electronegativity of a N atom is higher than that of a C atom, whereas the electronegativity of a B atom is lower than that of a C atom. Therefore, it is expected that an N = B/N-B structure in a carbon framework will exhibit much higher chemisorption for both lithium polysulfi des and Li 2 S. Hence, we present a strategy to chemically bind sulfur and its discharge products with a graphene-supported N/B codoped carbon layer with unique N = B/N-B sites and various kinds of N sites (pyrrolic N and pyridinic N) in the surface carbon framework.It would be a great challenge to synthesize the N = B/N-B structure by introducing the N and B separately into carbon framework because of the low percentage of heteroatoms in N/B-doped carbon materials. Therefore, our synthetic strategy is quite different. In our strategy, ionic liquid (IL, in particular [Emim]BF 4 ) was fi rst introduced to functionalize a graphitic The high theoretical energy density (2600 Wh kg −1 ) and the low cost of sulfur have made lithium-sulfur (Li-S) batteries an attractive option to satisfy the need for advanced energy storage. [ 1 ] However, there are several challenges. Foremost among these is the shuttling effect arising from the dissolution of lithium polysulfi des intermediat...

Foldable interpenetrated metal-organic frameworks/carbon nanotubes thin film for lithium–sulfur batteries

“…3a), which is as good as those reported before293031. Moreover, excellent cyclability over 500 cycles with a small fading rate of 0.08% per cycle at 0.2 C and high coulumbic efficiency above 99% are also achieved.…”

Intertwined Nitrogen‐Doped Carbon Nanotube Microsphere as Polysulfide Grappler for High‐Performance Lithium‐Sulfur Batteries

“…[36] The peak pattern of the SCNT/S spectrum indicates that the sulfur still appears in the crystalline form, but its peak intensity is weakened, indicating that the sulfur has successfully entered the internal pores of the carbon material. [39] These results show that the one-step atomization doping process has successfully doped nitrogen into the carbon nanotube microspheres, and some nitrogencontaining functional groups have also been formed in the NSCNT/S composites. The sulfur content in the carbon nanotube microsphere/sulfur composite can be determined.…”

Hierarchically Porous Multilayered Carbon Barriers for High‐Performance Li–S Batteries

“…According to the N 1s spectra, the nitrogen contents for N‐ZDC 1 , N‐ZDC 2 , N‐ZDC 3 and N‐ZDC 4 are 3.5, 3.8, 4.1, and 4.2 %, respectively (Figure d). Nitrogen doping could not only improve the surface wettability of a carbon matrix, but also helps to immobilize lithium polysulfides by additional chemical interaction of the N atoms with the polysulfides and consequently further enhances the electrochemical performance …”

“…It has been reported that the conductivity of carbon materials can be enhanced by doping with heteroatom elements, such as N and B . More importantly, strong interactions between Li 2 S n and N atoms in the carbon matrix exist according to density functional theory and diffusion experiments . Hence, the surface adsorption of sulfur species on carbon hosts is largely improved, which in turn allows a reduced lithium polysulfides dissolution and an enhanced sulfur utilization.…”