Here we demonstrate pronounced suppression of self-discharge using an ionic liquid of N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide-based electrolytes for Li–S batteries.

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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...