Evaluating the role of nitrogen in carbon hosts for aqueous zinc sulfur batteries

Aqueous Zn–S batteries exhibit high capacity, energy density, low cost, and safety performance, making them a promising energy storage system. However, the practical application is restricted by poor conductivity of sulfur, slow sulfur redox kinetics, and high energy barriers. Herein, density functional theory (DFT) was first adopted to simulate and design carbon hosts for Zn–S batteries. According to DFT results, nitrogen doping could increase the average adsorption energy from -0.05 eV to -3.60 eV, and reduce the energy barrier of the electrode reaction from 1.65 eV to 0.67 eV. The charge density difference indicates that the nitrogen atoms provide electronic channels and enhance the charge transfer between carbon and polysulfides. Secondly, various carbon hosts were synthesized for experimental evaluation of Zn–S batteries. Compared to undoped cathode (AC/S), the nitrogen doped cathode (NC/S) exhibits a higher initial specific capacity of 316.4 mAh g −1 at 0.2 A g −1 . After 100 cycles, its capacity retention rate is up to 82.5%. Meanwhile, the charge transfer rate and electrochemical conversion kinetics of NC/S cathode are significantly enhanced. The experimental results have successfully confirmed the prediction of the DFT study. This work has revealed the essence of nitrogen doping in depth, which provides a paradigm of how to rationally design cathode materials.