Biochar has been widely studied in recent years and plays an important role in energy storage and environment conservation. Heteroatom-doped biochar with open structures (3-D hierarchical porosity and 2-D nanosheet) exhibits good performances in recharged batteries and supercapacitors. Heteroatoms (O, N and S) can support more active sites to improve the reversible capacities of carbon-based electrodes, and open structures can offer rapid transport channels for ions and electrons to improve the rate performance of the electrodes. However, high preparation temperatures (generally over 800 °C) are needed to ensure sufficient activation to form open structures, resulting in a significantly elimination of surface heteroatoms. In this abstract, we described a simple and inexpensive method to prepare biochar with both high N/O contents and open structure. Cattle bones were used as precursors and KOH was used as an activator. Different from other carbon materials that were prepared by KOH activation, tremella-like hierarchical porous carbon nanosheets (HPCNS) were obtained at 550 °C due to a hydroxyapatite (HA)-KOH synergism. During the thermo treatment process, KOH broke the carbon coating of HA by the activation and facilitated the recrystallization of HA. At the same time, the recrystallized HA provided new space for KOH to penetrate into the monoliths and enhanced the activation. Due to this HA-KOH synergism, a 3-D/2-D structure was generated under a relatively low temperature, and numerous N and O atoms were maintained. The N and O contents analyzed by the XPS were as high as 6.4 and 17.1 %, respectively. Besides, HPCNS possessed high defects on carbon layers and high structural defects (large carbon interlayer distance of 0.41 nm) due to the enhanced activation caused by the HA-KOH synergism. Beneficial from the high defects, high heteroatom contents and unique 3-D/2-D structure, HPCNS electrode for Na-ion battery delivered a high reversible capacity of 198.5 mAh g-1 after 1000 cycles at 2 C (1 C= 0.35 A g-1), and 150.8 mAh g-1 after 10000 cycles at 20 C, showing superior rate and long cycle performance.

Tremella-like N,O-codoped hierarchical porous carbon nanosheets derived from cattle bone for fast and stable sodium storage

253rd National Meeting (2017)

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