Nitrogen-Doped Hollow Carbon Nanospheres for High-Performance Li-Ion Batteries.

N-doped carbon materials is of particular attraction for anodes of lithium-ion batteries (LIBs) because of their high surface areas, superior electrical conductivity, and excellent mechanical strength, which can store energy by adsorption/desorption of Li at the interfaces between the electrolyte and electrode. By directly carbonization of zeolitic imidazolate framework-8 nanospheres synthesized by an emulsion-based interfacial reaction, we obtained N-doped hollow carbon nanospheres with tunable shell thickness (20 nm to solid sphere) and different N dopant concentrations (3.9 to 21.7 at %). The optimized anode material possessed a shell thickness of 20 nm and contained 16.6 at % N dopants that were predominately pyridinic and pyrrolic. The anode delivered a specific capacity of 2053 mA h g at 100 mA g and 879 mA h g at 5 A g for 1000 cycles, implying a superior cycling stability. The improved electrochemical performance can be ascribed to (1) the Li adsorption dominated energy storage mechanism prevents the volume change of the electrode materials, (2) the hollow nanostructure assembled by the nanometer-sized primary particles prevents the agglomeration of the nanoparticles and favors for Li diffusion, (3) the optimized N dopant concentration and configuration facilitate the adsorption of Li; and (4) the graphitic carbon nanostructure ensures a good electrical conductivity.