Oxygen defects boost polysulfides immobilization and catalytic conversion: First-principles computational characterization and experimental design

Abstract

Although some experiments have shown that point defects in a cathode host material may enhance its performance for lithium-sulfur battery (LSB), the enhancement mechanism needs to be well investigated for the design of desired sulfur host. Herein, the first principle density functional theory (DFT) is adopted to investigate a high-performance sulfur host material based on oxygen-defective TiO2 (D-TiO2). The adsorption energy comparisons and Gibbs free energy analyses verify that D-TiO2 has relatively better performances than defect-free TiO2 in terms of anchoring effect and catalytic conversion of polysulfides. Meanwhile, D-TiO2 is capable of absorbing the most soluble and diffusive long-chain polysulfides. The newly designed D-TiO2 composited with three-dimensional graphene aerogel (D-TiO2@Gr) has been shown to be an excellent sulfur host, maintaining a specific discharge capacity of 1,049.3 mAhg−1 after 100 cycles at 1C with a sulfur loading of 3.2 mgcm−2. Even with the sulfur mass loading increasing to 13.7 mgcm−2, an impressive stable cycling is obtained with an initial areal capacity of 14.6 mAhcm−2, confirming the effective enhancement of electrochemical performance by the oxygen defects. The DFT calculations shed lights on the enhancement mechanism of the oxygen defects and provide some guidance for designing advanced sulfur host materials.