Facilitation of sulfur evolution reaction by pyridinic nitrogen doped carbon nanoflakes for highly-stable lithium-sulfur batteries

Lithium-sulfur batteries have been highly praised for energy storage on account of their high theoretical energy density. Beside the dissolution of lithium polysulfides, volume expansion during lithiation and insulation nature of sulfur, which lead to low sulfur utilization, the irreversible phase transformation of the final discharge product Li2S is considered as one predominant reason for capacity fading of lithium-sulfur batteries. The effective activation of Li2S is the key to improve the cycling stability. Herein, we develop a cost-effective method to synthesize N-doped nanoflakes with tunable nitrogen structures and controllable concentrations. Activation experiments confirm that N-doped carbon can reduce the activation energy to accelerate the Li2S conversion for the first time. The pyridinic N doped carbon exhibits not only the strongest capture ability of the lithium polysulfides but also the lowest dissociated energy of Li2S. Moreover, theoretical and experimental evidence prove that the activity site is electron-withdrawing pyridinic N. The cathodes based on pyridinic N doped carbon display higher capacity and better cycling stability.