Abstract
The commercialization of high-energy-density and low-cost lithium-sulfur batteries has been severely impeded by capacity fading and electrochemical polarization. Here we report a strategy to entrap polysulfides and boost the cathodic redox kinetics by embedding the surface oxidized quantum-dot-size TiN (TiN-O) within the highly ordered mesoporous carbon matrix. While the carbon scaffold offers sufficient electrical contact to the insulate sulfur, benefiting the full usage of sulfur and physical confinement of polysulfides. The surface oxygen renders TiN-O with a strong charge polarization effect for polysulfides via S-O-Ti bond as verified experimentally and theoretically. The suppressed shuttle effect and high lithium ion diffusion coefficient (7.9 × 10−8 cm2 s−1) lead to a high capacity of 1264 mA h g−1 at 0.2 C with a negligible capacity fading rate of 0.06% per cycle. Additionally, TiN-O based prototype soft-package cells also exhibit excellent cycling stability with flexibility, demonstrating their potential for practical applications.
Highlights
The commercialization of high-energy-density and low-cost lithium-sulfur batteries has been severely impeded by capacity fading and electrochemical polarization
We report a rational design on structure and surface chemistry by employing the highly ordered mesoporous carbon (OMC) as matrix and the surface oxidized quantum-dot-size TiN (TiN-O) as polysulfide mediator for suppressing shuttle effect and boosting redox kinetics
The transmission electron microscopy (TEM) observations reveal that the as-prepared OMC successfully replicated highly ordered mesoporous structure of SBA-15 with pores size of approximate 3.5 nm and ~9.9 nm in the wall thickness (Fig. 1b and c)
Summary
The commercialization of high-energy-density and low-cost lithium-sulfur batteries has been severely impeded by capacity fading and electrochemical polarization. We report a rational design on structure and surface chemistry by employing the highly ordered mesoporous carbon (OMC) as matrix and the surface oxidized quantum-dot-size TiN (TiN-O) as polysulfide mediator for suppressing shuttle effect and boosting redox kinetics. The experimental studies show a good consistency that TiN-O-OMC electrode delivers a superior electrochemical catalytic performance with the lowest overpotential of 271 and 465 mV at 0.2 and 5 C and highest lithium ion diffusion coefficient of 3.6 × 10−8 cm[2] s−1 (Li2S42− → Li2S) This rationally designed architecture and surface chemistry of TiN-O leads to a high capacity of 1395 mA h g−1 at 0.1 C, a Coulombic efficiency approaching 100% and a high-rate performance of 726 mA h g−1 at 5 C. The as-developed sulfur cathode exhibits great potential for practical applications as demonstrated by the pouch cell with an initial discharge capacity of 845 mA h g−1 at 0.2 C and stable cycling performance of 634 mA h g−1 after 120 cycles
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