Low Temperature Pyrolyzed Soft Carbon as High Capacity K-Ion Anode

K-ion batteries (KIBs) are emerging as an alternative solution for large-scale energy storage. Carbon materials, including graphite and nongraphitic carbons such as soft carbons and hard carbons, have been studied as anode materials for K-ion storage. However, to date, it has been rarely reported that bulk carbon anode materials could reach a capacity of 350 mAh/g, given in a potential range of 0-2 V. Herein, we report that soft carbon (SC) obtained by annealing an organic molecular solid of PTCDA at a low temperature of 700 degrees C demonstrates a reversible capacity of 350 mAh/g, excellent rate capability, and good cycling performance. Characterization, including neutron total scattering and pair distribution function studies, shows that this high-capacity material is composed of extremely small graphitic fragments with a large number of edge-defect sites. The extra capacity of the low temperature pyrolyzed soft carbon comes from a potential range from 0.6 to 2.0 V vs K+/K. The computational studies reveal that K-ions bind armchair edge sites at 1.5 V but bind point defects of monovacancy and divacancy at much lower potentials around 0.3 V. This study suggests that the additional capacity may correlate to abundant edge defects of soft carbon domains for K-ion storage.