Novel carbon-based microporous nanoplates containing numerous heteroatoms (H-CMNs) are fabricated from regenerated silk fibroin by the carbonization and activation of KOH. The H-CMNs exhibit superior electrochemical performance, displaying a specific capacitance of 264 F/g in aqueous electrolytes, a specific energy of 133 Wh/kg, a specific power of 217 kW/kg, and a stable cycle life over 10000 cycles.

To understand the origin of enhanced electrochemical performances of MgO-coated LiCoO 2 as cathode materials for lithium ion battery, we investigate the internal structures of the materials at the nanometer scale. The MgO-coated LiCoO 2 are annealed at various temperatures of 750−810 °C so as to find the optimized heat-treatment condition. The surface morphologies and crystalline structures are characterized by SEM, TEM, EELS, and XRD. The electrochemical results show that the MgO-coated LiCoO 2 delivers a high capacity with excellent retention property. In particular, the sample annealed at 810 °C, which possesses the high doping level of Mg 2+ ion in the Li sites, exhibits the highest retention capacity without undergoing phase transformation in the interfaces between the MgO-coating layer and the bulk LiCoO 2 during cycling. Lithium and vacancy ordering in the delithiated state is monitored by TEM measurements. By comparison with the bare LiCoO 2 , we reveal that the MgO-coating layer plays a role in the prevention of lithium and vacancy ordering in the near-interfaces, which is in agreement with the excellent electrochemical cycling performances of the MgO-coated sample annealed at 810 °C. As a result, depending on the thermal treatment temperature, the Mg 2+ ions from MgO layer diffuse into Co and Li sites in LiCoO 2 , competitively, and affect the structural stability and electrochemical performances.

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