Retarding graphitization of soft carbon precursor: From fusion-state to solid-state carbonization

The soft carbon precursor pitch, featured with low-cost and easy-availability, is regarded as a very promising candidate for the synthesis of carbonaceous anode. However, the Na-storage performance of pitch-derived carbon is strongly hindered by its highly graphitized structure, which mainly comes from the reordering during the fusion-state carbonization. To prevent the graphitization, herein, we propose an in-situ Mg(NO3)2·6H2O solidification strategy to convert the fusion-state to solid-state carbonization. The oxygen species and solid products generated from the decomposition of Mg(NO3)2·6H2O can retard the melting and reordering of pitch, thus tailoring the microstructure. The optimal sample displays outstanding overall performances in both half- and full-cells, with ~3-fold increase in capacity. Particularly, the carbon yield is significantly increased from 61% to 92% because less organic molecules can escape. The understandings gained in this work not only offer insights to adjust the carbonization process, but also provide solutions to obtain highly disordered carbon anodes from soft carbon precursors.