Nitrogen‐doped carbons were synthesized by a solvent‐free mechanochemically induced one‐pot synthesis by using renewable biomass waste. Three solid materials are used: sawdust as a carbon source, urea and/or melamine as a nitrogen source, and potassium carbonate as an activation agent. The resulting nitrogen‐doped porous carbons offer a very high specific surface area of up to 3000 m2 g−1 and a large pore volume up to 2 cm3 g−1. Also, a high nitrogen content of 4 wt % (urea only) up to 12 wt % (melamine only) is generated, depending on the nitrogen and carbon sources. The mechanochemical reaction and the impact of different wood components on the porosity and surface functionalities are investigated by nitrogen physisorption and high‐resolution X‐ray photoelectron spectroscopy (XPS). These N‐doped carbons are highly suitable as cathode materials for Li–S batteries, showing high initial discharge capacities of up to 1300 mAh gsulfur−1 (95 % coulombic efficiency) and >75 % capacity retention within the first 50 cycles at low electrolyte volume.

The lithium-sulfur (Li-S) battery is a promising alternative to overcome capacity and specific energy limitation of common lithium-ion batteries. Highly porous carbons with nitrogendoping as conductive host structure for sulfur/lithiumsulfide deposition are shown herein to play a critical role in reversible cycling at low electrolyte/sulfur ratio. The pore geometry is precisely controlled by an efficient, scalable ZnO hard templating process. By using an electrolyte volume as low as 4 μl mg-1 S , the beneficial nitrogen functionality leads to a twofold increased cell lifetime turning our findings highly favorable for real applications. Stable cycling of up to 156 cycles (59 cycles with undoped carbon) with high sulfur loadings of 3 mg cm-2 is achieved. Operando X-ray diffraction patterns during cycling show the transformation pathway of the sulfurpolysulfide-Li 2 S species. The observed intermediates critically depend on the nitrogen doping in the cathode carbon matrix. Nitrogen doped carbons facilitate polysulfide adsorption promoting the nucleation of crystalline Li 2 S. These results provide new insights into the significant role of heteroatom doping for carbons in Li-S batteries with high specific energy.

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