Thick free-standing electrode based on carbon-carbon nitride microspheres with large mesopores for high-energy-density lithium-sulfur batteries

Abstract

The development of sulfur cathodes with high areal capacity and high energy density is crucial for the practical application of lithium-sulfur batteries (LSBs). LSBs can be built by employing (ultra) high-loading sulfur cathodes, which have rarely been realized due to massive passivation and shuttling. Herein, microspheres of a carbon-carbon nitride composite (C@CN) with large mesopores are fabricated via molecular cooperative assembly. Using the C@CN-based electrodes, the effects of the large mesopores and N-functional groups on the electrochemical behavior of sulfur in LSB cells are thoroughly investigated under ultrahigh sulfur-loading conditions (>15 mgS cm(-2)). Furthermore, for high-energy-density LSBs, the C@CN powders are pelletized into a thick free-standing electrode (thickness: 500 mu m; diameter: 11 mm) via a simple briquette process; here, the total amount of energy stored by the LSB cells is 39 mWh, corresponding to a volumetric energy density of 440 Wh L-1 with an areal capacity of 24.9 and 17.5 mAh cm(-2) at 0.47 and 4.7 mA cm(-2), respectively (at 24 mgS cm(-2)). These results have significantly surpassed most recent records due to the synergy among the large mesopores, (poly)sulfide-philic surfaces, and thick electrodes. The developed strategy with its potential for scale-up successfully fills the gap between laboratory-scale cells and practical cells without sacrificing the high areal capacity and high energy density, providing a solid foundation for the development of practical LSBs.