Unraveling the hierarchical porous structure in natural pollen-derived Fe-containing carbon to address the shuttle effect and dead sulfur problems in lithium-sulfur batteries

Abstract

Mesoporous carbon–metal composites with the merits of strong adsorption ability over soluble lithium polysulfides (LiPSs), excellent sulfur dispersion, high conductivity, low cost, and rapid catalytic conversion rate to suppress the shuttle effect are promising in lithium-sulfur batteries. However, their application is usually limited by structural collapse and fast fading because of the poorly dispersed metal-based compounds in the mesoporous carbon host during high-temperature synthesis. Herein, a 3D rape pollen-derived carbon (RPDC) containing Fe-based compounds as the sulfur host is prepared through the solid-state reaction of simultaneous carbonization between natural rape pollen and ferrous oxalate. Characterizations confirm that Fe-RPDC composites have stronger physiochemical adsorption and catalytic ability than pure RPDC, Fe-doped commercial activated carbon, and pure Fe3O4. Then, soluble LiPSs are adsorbed, fixed on the surface of the Fe-RPDC composites and catalyzed by Fe-based compounds to reduce the “dead sulfur”. Finally, a mature natural structure-derived hollow carbon-iron compound system is developed. The lithium-sulfur battery assembled using Fe-RPDC as host showed excellent long-term stability and a high electron transport rate. The Fe-RPDC@S composite with 69.6 wt% sulfur content exhibits the highest initial discharge capacity of 955.7 mA h g−1 at a rate of 1 C and can be maintained at 556.3 mA h g−1 even after 150 cycles. The decay rate is only 0.03 % per cycle, and the average Coulomb efficiency is approximately 98 %. Hence, the reasonable design of Fe-RPDC composites is of great significance for promoting the transformation of polysulfide intermediates and chemically anchoring soluble LiPSs to restrain “dead sulfur” and can be used to realize low-cost, green and large-scale production.