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.