A one-step hard-templating method for the preparation of a hierarchical microporous-mesoporous carbon for lithium-sulfur batteries

Porous carbon materials can increase the conductivity of sulfur and restrain the shuttling of polysulfides in the electrolyte. A hierarchical microporous-mesoporous carbon (HMMC) with a large surface area and pore volume was prepared by the simple one-step carbonization of a mixture of magnesium gluconate (MG) and phenolic resin. The MG was transformed into nanosize magnesium oxide that acted as a hard template during carbonization to create mesopores. The HMMC has a high surface area (∼1 560 m 2 g −1 ) and large pore volume (∼2.6 cm 3 g −1 ), which provides abundant space for sulfur loading and accommodates volume changes during charge/discharge. The interconnected pore structure and carbon framework ensure fast electron and Li ion transfer. As the cathode of a Li-S battery the sulfur-loaded HMMC has a high discharge capacity of 939 mAh g −1 at 0.3 C and a reversible capacity of 731 mAh g −1 after 150 cycles with only a 0.15% capacity fade per cycle. Even at a high rate of 2 C, it still delivers a high discharge capacity of 626 mAh g −1 , showing an excellent rate performance.