Sulfur Grafted Hollow Carbon Spheres for Potassium Ion Battery Anodes

Sulfur-rich carbons are minimally explored for potassium ion batteries (KIBs). Here, we chemically incorporate a large amount of S (38 wt. %) into a carbon host, creating Sulfur-grafted Hollow Carbon Spheres (SHCS) for KIB anodes. The SHCS architecture provides a combination of nanoscale ( ca. 40 nm) diffusion distances and C-S chemical bonding to minimize cycling capacity decay and Coulombic efficiency (CE) loss. SHCS exhibits a reversible capacity of 581 mAh g -1 (at 0.025 A g -1 ), which is the highest reversible capacity reported for any carbon-based KIB anode. Electrochemical analysis of S-free carbon spheres baseline demonstrates that both the carbon matrix and the sulfur species are highly electrochemically active. SHCS also shows excellent rate capability, achieving 202, 160 and 110 mAh g -1 at 1.5, 3 and 5 A g -1 , respectively. The electrode maintained 93% of the capacity from the 5 th to 1000 th cycle at 3 A g -1 , with steady-state CE being near 100%. Raman analysis indicates reversible breakage of C-S and S-S bonds upon potassiation to 0.01 V vs. K/K + . GITT analysis provides voltage - dependent K + diffusion coefficients that range 10 -10 to 10 -12 cm 2 s -1 upon potassiation and depotassiation, with approximately five times higher coefficient for the former.