A solvothermal pre-oxidation strategy converting pitch from soft carbon to hard carbon for enhanced sodium storage

Due to its low cost and easy availability, the pitch is considered a promising precursor for soft carbon anodes. However, pitch-derived soft carbon shows a high graphitization degree and small interlayer spacing, resulting in its much lower sodium storage performance than hard carbon. We propose a novel pre-oxidation strategy to introduce additional oxygen atoms into the low-cost soft carbon precursor pitch to fabricate a defect-rich and large-interlayer spacing hard carbon anode (HPP-1100). Compared with the direct pyrolysis of pitch carbon, the sodium storage capacity of HPP-1100 is significantly improved from 120.3 mAh/g to 306.7 mAh/g, with an excellent rate and cycling capability (116.5 mAh/g at 10 C). Moreover, when assorted with an O3-Na(NiFeMn) 1/3 O 2 cathode, the full cell delivers a high reversible capacity of 274.0 mAh/g at 0.1 C with superb cycle life. This work provides a new solution for realizing the application of low-cost pitch anodes in Na-ion batteries. Converting soft carbon precursors to hard carbon via a solvothermal pre-oxidation strategy significantly increases the sodium storage capacity from 120.3 mAh/g to 306.7 mAh/g.