Sulfur-grafted hard carbon with expanded interlayer spacing and increased defects for high stability potassium-ion batteries

Carbon materials have been proven to be an effective anode for potassium-ion batteries (PIBs) due to their high safety, low cost, and environmental benignity. However, the repeated insertion/extraction of K-ions with a larger size into/from electrode at low voltage region will inevitably cause obvious volume expansion, easily resulting in poor cycle stability. Hence, we synthesize S-doped hard carbon material (NSHCM2) using biomass as carbon and thiourea as S sources. Various characterizations demonstrate that the introduced S-heteroatom not only expands the distance between carbon layers, but also creates more defects. The former ensures the free intercalation/ deintercalation of K-ions without structure deformation, while the latter can provide numerous active sites to adsorb K-ions, all these together contribute to structure stability and reversible capacity. As a result, the opti-mized NSHCM2 electrode delivers a high capacity of 294 mAh g-1 at 200 mA g-1 and an ultra-long cycling stability by achieving 220 mAh g-1 at 2000 mA g-1 over 5000 cycles. This simple and high effective synthesis route makes durable and fast potassium storage possible.

Automated summary

Graphene materials have been found to be effective anodes for potassium-ion batteries due to their safety, low cost, and environmental friendliness. However, the repeated insertion/extraction of large-sized K-ions into/from the electrode at low voltage regions often leads to volume expansion and poor cycle stability. To address this issue, researchers have synthesized S-doped hard carbon material (NSHCM2) using biomass and thiourea, which has been found to expand the distance between carbon layers and create more defects, resulting in improved structure stability and reversible capacity. The optimized NSHCM2 electrode exhibits a high capacity of 294 mAh g-1 at 200 mA g-1 and excellent cycling stability of 220 mAh g-1 at 2000 mA g-1 over 5000 cycles. This simple and effective synthesis route enables durable and fast potassium storage.