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 μm; 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.