Hierarchical porous carbon sheets derived from biomass containing an activation agent and in-built template for lithium ion batteries

We report a new strategy for synthesizing two-dimensional (2D) hierarchically porous carbon (HPC) based on soft pitch as the carbon source and oyster shell as both the template and activation agent precursor. The confined space of the sheet-like CaCO3 in oyster shell allows the soft pitch to diffuse and coat the in-built template, and the resultant 2D carbon derived from pyrolysis of the pitch inherited the sheet-like morphology of the template. Furthermore, CaCO3 can be easily converted into CaO, which acts as the self-activation agent to produce interconnected micro-, meso-, and macroporous carbon networks. The specific surface area of the resultant HPC was tuned from 612 to 1258 m2 g−1 by varying the pyrolysis time at 900 °C, and the resulting micro/meso-pore sizes were in the range of 0.7–9.5 nm. When used as the electrode of a lithium ion battery (LIB), the HPC exhibited a high reversible capacity of 1251 mAh g−1 at 0.1 A g−1 with excellent cycle stability. These results indicate that the 2D layered structure might effectively shorten the solid-state diffusion distance for Li ions in a LIB during the charging and discharging process. The interconnected hierarchical porous structure also improved the capacitance.