Rationalizing nitrogen-doped secondary carbon particles for practical lithium-sulfur batteries

Nanostructured carbon host materials are widely used to improve both sulfur utilization rate and reaction kinetics in lithium-sulfur (Li-S) batteries. However, high complexity/cost of materials synthesis and difficulty in processing nano-materials into high-mass-loading electrodes are still significant barriers to the development of low-cost and high-energy Li-S batteries. In this study, we reported a generic and scalable synthesis approach to prepare nitrogen-doped secondary carbon particles. By using nitrogen-containing precursor as an integration reagent, the nanosized Ketjen Black particles were integrated into micron-size secondary ones and nitrogen-doped (NKB) simultaneously through a one-step heat treatment. With NKB as an example material, the effects of particle integration degree on the secondary particles' structures, pore volume and connectivity, sulfur loading capability, and cell performance were studied and discussed. At an optimal integration condition, the NKB particles had significantly improved particle dimensions with well-maintained high specific surface area and pore volume. Contributed by the micron size and high pore volume, the NKB/S were successfully used for high-sulfur-loading cathode coating (4-7 mg s cm(-2)) and were able to deliver a specific capacity of similar to 1100 mAh g(-1)at a practical low-porosity (50 %) and lean-electrolyte conditions (E/S =4 mu L. mg(-1)). Feasibility of the materials for practical use was validated through scaling up synthesis (40 g/batch), large-area electrode coating, and practical pouch cell (1.6 Ah) assembly and test.

Automated summary

In this study, a generic and scalable synthesis approach was reported to prepare nitrogen-doped secondary carbon particles, which significantly improved the performance of lithium-sulfur batteries. By optimizing the particle structure and porosity, high-sulfur-loading and high specific capacity were achieved.