Oxygen self-doping pyrolyzed polyacrylic acid as sulfur host with physical/chemical adsorption dual function for lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries with high theoretical capacity and energy density need to solve problems such as the high decomposition energy barrier of Li2S and large volume change of sulfur in the charging process caused by the shuttle effect before practical application. Herein, a green synthesis method is used to prepare polyacrylic acid (PAA) superabsorbent material, and then the pyrolyzed PAA (P/PAA) material is obtained as the positive electrode of Li-S battery. Density functional calculation reveals that the oxygen self-doping pyrolyzed polyacrylic acid (P/PAA) delivered stronger binding energy toward Li2S species in carbonyl C=O than that of graphite powder (GP) which are −1.58 eV and −1.02 eV, respectively. Coupled with the distribution of relaxation time analysis and the in-situ electrochemical impedance approach, it is further demonstrated that the designed P/PAA as sulfur host plays a physical/chemical adsorption dual function in maintaining the stability and rate performance of batteries. With an initial discharge capacity of 1258 mAh/g at 0.1 C and a minimal capacity decline of 0.05% per cycle even after 800 cycles at 0.5 C, the produced cathode demonstrated outstanding electrochemical performance. The average Coulombic efficiency is nearly 100%. The P/PAA electrodes may typically retain 96% of their capacity while declining on average only 0.033% per cycle after 130 cycles at 3 C. This effort provides a new method for the future development of heteroatomic self-doping superabsorbent with promising adsorption properties for polysulfides as cathode materials of Li-S batteries.